Replace a Sram x7 trigger lever?

Question: I broke the lever of my shifter (SRAM X7) when I fell off my bike on a trail. I think it just fell off the unit. I can see where the lever is connected to the mechanism that pulls the cable. Can I replace just the lever, and not have to buy the entire shifter?
Answer: It's extremely unlikely that you will be able to buy parts for a cheap shifter. The whole unit costs $US25 with free shipping.
Imagine you could buy just the lever wholesale for $3. Then you'd pay the wholesaler $3 to find it and pack it for you, then the $3 postage cost. So your "$3" part is going to cost you $9. Plus you're probably going to want the mounting parts for that lever, but they're unlikely to be available separately (the economics get even worse for 2c screws), so there will be a kit of parts including the lever, ratchet mechanism and whatever attaches it to the body. But that kit costs $10 plus the $6 S&H. So you have saved $9 over buying a whole new lever.
Now the shop cuts the old cable off the bike, installs the new parts, new gear cable and outer, and set everything up. Which is about $20-$40 of labour, plus $10 for the cable and outer.
The total cost is about $16 + $10 + $20 = $46-$66. Or $55 for a whole new lever, fitted. New whole lever is an easy job, taking apart the old one is tricky so will probably take longer.
From a bike shop's point of view that's a $9 saving in exchange for the risk that you're wrong about how much damage was done. If the pivot that that lever sits on has bent the repaired lever won't work properly. There's a whole range of problems like this, but you as the customer won't care, you will just come in and say "you fixed it, but it doesn't work". After the first time this happened they stopped doing it, and only fit whole new parts.
So bike shops will not order the "parts kit", only a few keen cyclists who do their own repairs will. Instead of selling hundreds of these kits, SRAM will only sell ten. And maybe another ten next year. Or not, since the overhead cost of each product is non-trivial and if something is only going to sell a hundred units at $10 they're not going to bother.
Which is what you see happening.
Comment: Good explanation of economics and why parts cost so much.
Comment: Thanks for your answer!!!!! very informative! and smart, I will buy the whole shifter then... probably in a local shop to get free instalation! so the economics make sense.
Answer: @Moz has provided a very good answer to this, however, do hunt around on eBay for what-you-may-find, you also might have one of those bike shops nearby that keep broken-but-useful parts (where they may have what you want) and also be aware that these levers come in a set, you only want one (a replacement) not the set of two.
Consult your LBS.

Replace a Sram x7 trigger lever?


Second Law of Thermodynamics, heat and quantum-level explanation

Question:
I heard somewhere that the second law of thermodynamics is stating that some heat (energy) becomes unusable for work (at the scale of the whole universe). Why is it like that? Can't heat be converted into some energy forms? I do understand that entropy is the measure of spontaneity, but I am having hard time understanding this.
How can we depict heat in relativistic (classical) level and quantum level? Is there heat energy that is not mediated by any form of particle?
Answer: There's an analogy based on viewing heat as a liquid e.g. water. You need to be a bit cautious with this as like all analogies it fails if pushed too far, but I think it helps with your question.
Anyhow, if heat is like water then temperature is like water pressure. If you have water at different pressures you can use the water to do work. This is how hydroelectric power stations work. But as you generate electricity from your power station the water flows from the high point to the low point, and eventually it will all be at the same level. Once this happens you can't get any work out of it because there's nothing to make the water flow. For a hydroelectric power station rainfall refills the upper reservoir, but for the universe as a whole once the heat is uniformly distributed that's it - there is nothing left to move the heat around so you can't extract any more work.
Re the second part of your question: suppose we have some heat (e.g. by burning coal) and we use this heat in a steam engine to pump water from a low point to a high point. Some of the heat has been turned into the potential energy of the water so in this sense the heat has been stored in a form that doesn't rely on particle motion.
Heat is just a form of energy, and all forms of energy are interchangable, though rarely (if ever) with 100% efficiency.
Answer: Actually heat is indeed usable as you state, but we should understand what it really means.
Heat is a way in which energy is transfered from one system to another. The other way is work. When we say that we use heat to produce work, we are making a conversion from one of these energy forms to the other. To do that, a differential in temperatures is necessary, otherwise no heat transfer can happen and much less work can be done.
The problem is that at some point, after transfering heat from temperature reservoir to ever lower temperature reservoirs, your heat becomes so dissipated, i.e. the temperature so low that you can't find lower temperature reservoirs anymore to continue dissipating the heat even more in the hope of producing some more work.
To use a bit of a different picture, think of a watermill. What drives the watermill to produce work is the height difference. Now, you say, once the water has gone through the mill, let's just put another mill below it. And after that one, another mill. But clearly, there must be an end to that process. So it is with heat.
I don't know about your second question though. I'll just say this, heat is the macroscopic result of work at a microscopic level that does not result in work at the macroscopic level. For instance, when heat gets transfered from a hot bucket to a cold bucket by contact, all that really happens is either the molecules mixing through each other or the molecules colliding and exchanging energy. Work does happen, but it's at the microscopic level between colliding molecules and not at the macrolevel in the sense that the buckets move or the water moves or something like that. Maybe that clears up your second question.
So, the quantum level explanation of heat is not really markedly different from a classical level explanation assuming molecules. The details of the microscopic processes are different, but they are not really relevant to the macroscopic process, unless maybe you look at quantum processes that have some macroscopic consequences.


How do I get higher career ranks?

Question: I get messages from time to time saying I got "promoted" in my career, but I can't figure out what triggers that.
Answer: When you go to your charecter screen (click on your portrait/avatar in the main menu), you have an option to view your "career progress". In there you'll notice that you have a progression bar made of several levels for each of the main factions (Eco, Tech & Tycoon). The progress bar is made of ranks represented by circles. Each circle has its own progression bar that is filled by gaining career points for that faction.
The messages that you got that you have advanced your career, ment that you have gained enoughf career points with one of the fanctions to gain a new level.
Each level gained gives you rewords, avatars for your profiles, more upgrade slots at the arc, colors and formulas for the academy.
You gain career points for accomplishing goals at the main campeign, comptiting the daily quest for a certain faction (the faction that you chose will give you the points), global events, senate votes and maybe for some of the achievments (i.e make so and so quest for that faction).
Answer: From what I have read, you get experience from performing certain actions: such as watching a video for the first time should give you 200+ xp per faction or performing a global mission would do the same.
Also, "The gameplay includes 'World Events' - special missions only offered for a limited time, allowing all players to band together and complete the missions. Completing missions will reward players depending on how many people participate."
Source: http://en.wikipedia.org/wiki/Anno_2070

How do I get higher career ranks?


Do HTML comments () affect SEO?

Question: Is there any way that too many HTML comments in a document can effect search engine rankings?

Do the spiders ignore all of them?
Comment: Its good practice to limit your comments, they do waste bandwidth.  Search engines might not care, but having unnecessary comments weighs down the total data you send to your clients.  This may not seem like much but it can and will add up.  Remove them if they are not necessary.
Answer: They are completely ignored so no, it doesn't affect rankings. The only problem might be if you have such a massive amount of text in comments, that it increases the load time significantly. Users might go elsewhere.
Answer: If you're using a server side language, you could always put some comments inside comment tags in that language. I do this for comments I don't want outputted, or for situations where I'm taking down a section and don't want people to be able to view it like so...
<?php // php comment example
/*

DON'T WANT ANYONE TO SEE THIS

*/
?>

Your HTML page will be smaller, but your PHP process will be interpretting more... not sure which is more efficient, so for me it comes down to need.
Answer: This is a debate within the SEO community but I think this can be an issue if overdone. While things like comments and scripts make no sense to a search engine spider, if over done they can still affect the code to content ratio which can dilute the effect of any optimization as the content which does affect rankings starts to be interfered with by the noise of scripts and comments that don't.
One of the worst examples of this I have seen is with the __VIEWSTATE field in ASP.NET with some CMSs that leave a massive block of encrypted gobbledygook in the middle of the markup to maintain state with the server.
As a rule I wouldn't worry about code to content ratio too much but definitely adhere to best practice (ask yourself what would Chuck Norris do and don't over do scripts/comments) and remember that the limit of the Google cache is about 101kb per page and this should be considered the absolute limit. Spiders will give up on anything larger than this.
There is a good discussion in this SEOMoz forum thread.

Do HTML comments () affect SEO?


Looking for examples of "thank you" e-mail designs

Question: I've been tasked with creating "thank you for attending" HTML e-mails/graphics for a number of events. I've already done a few, but they all need to look distinct and I'm running out of ideas. Does anyone know of a gallery that shows this type of design, or of any outstanding examples?
Answer: Why not go uber simple and make it about the actual copy rather than the design as such. You would be surprised how much it affects things.
It really depends of course, on what you want people to do with it.
I have often done very complicated and beautiful thank you emails.
But I have found that doing it really simple is interesting in itself.
For instance when people sign up to my service WeekendHacker I send a really simple mail back saying:

Hey thanks for signing up
You will have to include: Name, Project description and what skills
  you are looking for. If you want to
  keep your idea tight then you should
  at least specify the kind of tasks you
  are looking for You'll only receive
  one mail a day, curated; if you don't
  want to receive mails any more, just
  mail me. Have fun!

That's just my five cents.
Comment: Actually, "uber simple" was what they were doing before I got involved. They decided they didn't like simple, so they asked me to do something. My specific assignment is to take the copy given to me and figure out a way to make it "pop" graphically. If I send back plain text or text with just minimal decoration my boss will tell me I haven't done my job.
Comment: heh yeah I see what you are saying :)
Answer: I always enjoy looking through these galleries at Mail Chimp, which happens to be a pretty good service also.
Comment: This page is now broken.
Answer: Campaign Monitor has some great examples too:
http://www.campaignmonitor.com/templates/


How do I prepare my child for a sleepover?

Question: How do I prepare my kids for their first sleepover? What should I do if they want to come home?
Answer: On the parent side:
Talk to the host parents to make sure you know what the plan is. Will there be a party? Games? Pillow fights? Food? Candy? Bedtime rituals, bath, brushing teeth, prayers? Are there house rules? Get a guest list so you know what other kids will participate (are you okay with who is on the list?). Make sure you agree with the plan.
Also, agree with the host parents what to do if things don't go according to plan. At what stage do you want to be contacted? How bad are things allowed to turn before you want to pick up your child? Is there a "point of no return": at what time of night is the stay committed and the child must stay there? What are the host parents' plan in case of a real (medical) emergency?
On the child side:
Talk to your child about what they expect to happen. What do they want to happen (like activities)? What to they not want to happen (like bed-wetting)? Make sure the child understands what is allowed and what isn't, and what kind of situations qualify for being picked up in the middle of the night. Make sure that the child is comfortable with the host parents (they might have to soothe the child, and this had better work), and if the child is comfortable with all the other guests.
Expectations can be big, and even a successful sleepover might not be a happy one if some detail went badly. Try to steer the child's expectations; not too high, but still a fun event to look forward to.
Try to make the child grasp the most difficult thing: Understand that it won't be perfect, and no matter what happens, always try to make the best of it and enjoy the good bits.
Answer: We began preparing our kids for sleepovers by starting with late nights out. They would stay at a friend's house until a specific time and then come home. After a few repetitions, my kids would usually ask to stay over for the night. We found that starting slow and expanding was easier for the kids than being overwhelmed with the thought of an entire night out.


How do you keep the size of your application down (memory usage and physical storage size)?

Question: I have a personal project that I'm working on although it's quite audio and graphic-intense and I was wondering if you guys had any suggestions or solutions as to how one could keep the size and memory-usage of their application to a minimum? My application is an iPhone application and, as Apple always make clear, the application is only allowed to use a certain amount of memory (in terms of performance and actual size).
Answer: Start looking for more compression using other formats when dealing with audio and video. Also images tend to have compressed version like jpeg. But if your application need multimedia, it will be quite heavy.
Also maybe try asking the same on stackoverflow forums, there you may find a more expert solution
Answer: I do not agree about using compression, i.e. JPG.
Preferred format is PNG, and if You use JPG anyway it will be expanded in memory.
So for example reduce size of PNG and draw with small tiles, draw in rects instead all view and do so on.
Use Instruments to see where and how You have big allocations and try to reduce them.
Make all loading "lazy" so you can free resources when done and reload on demand.
As You make a lot of graphics, is fine drawing directly objects, instead of loading images and drawing. (even if apple says is better to load image for performance reason... the trade-off is between processor usage and memory..)
Answer: only load in memory what you are actively using, when done, release the resource, to free memory.


How to get my 2.5-year-old to stop chewing his upper lip?

Question: My 2.5-year-old son recently had a cold and his upper lip got sore. He took to biting it. His cold is now gone but he keeps chewing his upper lip and it hasn't healed yet.  We keep putting salve on it to try to heal it but he keeps chewing it off. Any suggestions?
Answer: Are his lips pretty chapped? I would keep putting salve (I assume that is like vaseline, or chapstick or something?)on his lip and probably around/under his nose - that skin is probably roughed up from having to wipe his nose so much.
Ask him if it is hurting or bothering him? Even if it is not visibly chapped, it could still be bothering him. Make sure he is getting plenty of liquids to hydrate his lips as that will help with the healing.
How long has it been since he had the cold? I am sure it will work its way over.
He may have started it during his cold but discovered its soothing effects, like nail biting. Does he normally have issues with anxiety? When he's doing it, ask him if something is bother him, or what is he worried about, etc. And then I would just distract him with something else.
And, when he's doing it, say "oops, looks like its time for some lip medicine (salve)" with the idea that he will learn to ask for it himself when his lip is bothering him.
Answer: My daughter did this a lot too (and sometimes still does when she is stuffed up).  We put an organic salve on it that had a strong eucalytus scent (I'm sorry, I don't remember the name at the moment of the specific brand we used when she was doing this all the time).  It helped with the chapping, made me feel better that she wasn't eating petroleum based products, and because of it's strong and not favorable flavor, she didn't like how it tasted and stopped chewing on her upper lip.  If you can find a salve he hates, you might have the same lucky outcome (we hadn't thought out the bad-taste part, it was just a happy accident for us).


Can I connect 3 screens to my iMac?

Question: I am trying to connect iMac to 2 other monitors as well as my TV. That is a total of 4 displays.
HERE IS MY PLAN!!!-(I'm not rich)
I have a 21.5 inch iMac that has one thunderbolt port but can also be used as a mini-dvi port. I want to connect that to a Cirago HDX3DP01 HydraDisplay X3 DP to 3 DP Multimonitor Adapter
This in theory will allow me to connect to 2 monitors with an open slot for my TV.  I do question the resolution output. The HydraDisplay supports up to 3840 x 1024 (3x 1280x1024). I'm not sure what that means. Which resolution is it? I know that the 21.5-inch iMac has a native resolution of 1920 by 1080 pixels, while the 27-inch iMacs are 2560 by 1440 pixels. This means at top resolution of the HydraDisplay is cannot support the native resolution of the IMac 21.5 nor the 27-inch. Will this matter when mirroring or sharing the screens as one? (disregarding the TV)
So, I have several questions:
1. Will this work?
2. Is resolution a big deal when sharing screens?
3. Has anyone ever tried this or have a better way of doing it besides expensive thunderbolt?
Answer: From the link I can only find the interface used is DisplayPort (not Mini Display Port or DVI) which to my knowledge are different standards which means item 1) would not work
For item 2) what is the purpose of having multiple displays? Are you repurposing extra displays or actually have an alternate need?
For item 3) I use a USB display monitor which allows me to connect multiple additional screens trough different USB ports in addition to my standard display out.
Answer: I have three screens....

I'm using a kensington universal adapter to add the extra one - I've ordered another (expecting delivery today actually) so I should be able to run four... will let you know how it goes...
EDIT - adding another kensington adapter did work...

EDIT2 - as a follow up I should mention that this is running Lion (worked with snow leopard) and to run the Kensington adapter on OSX you have to download drivers from the manufacturers site. Regarding CPU usage - there is an overhead - but it does depent on what you are doing with the screen. If you are playing a video it's really interesting to see what happens to CPU load when you move the video window from one screen to another...
Comment: What is the performance like, does it work ok with Mountain Lion? A lot of people report extra CPU usage, is that the case with your set up?
Comment: I've added content to my answer to address this.

Can I connect 3 screens to my iMac?


Is crouching in Quake Live useful?

Question: In Quake Live I see users crouching when using gaunt or shotgun. Is there any advantage to crouching? Or are these players doing it for no reason?
Answer: IMHO, no.
Let me explain: crouching allow you to reduce your exposed surface, making you a smaller target. It could be useful, but crouching has a downside: it impedes your mobility by reducing your speed.
Since most of the weapons allow somebody to one-shot or two-shot you, good speed and unpredictable movements are your greatest way to survive. That's why most of the time, crouching is the easiest way to die.
Answer: yes it is.
Crouching reduces the amount of surface exposed to a possible enemy hit, while it is pretty much useless to use while walking it is usually used in midair, especially if you're moving in an area where you are an easy target.
It is not a big deal tho, sometime people may miss you because you crouched, but good players know how to shoot
Answer: Crouching in an unexpected moment can save your life. One example is a shotgun infight - a crouch in the right second can negate a otherwise full hit. Same goes for rail gun fights at medium distance.
And yes, for gauntlet as well.
Comment: How does crouching with gauntlet do anything if both people gaunting are crouching?
Answer: When you crouch you move silently, I think most players crouch because they forget you can walk silently without crouching (I have it bound to shift). Either that or they are just doing it because they can.
Comment: yeah and silent walk is also faster than crouching
Answer: In some situations, I find it to be very useful :)
In some maps, e.g. in Asylum (screenshot), you can crouch and shoot through the gaps between a wall and the floor :) You'll have to aim quite precisely, but it can be a very effective technique. Your target will most likely not expect it / won't immediately realize where the shots are fired from, so there's more chance of dealing fatal damage. At least, that's what it does for me. (oh noes, blew my cover)
I don't think it's of much use to have both players crouching, but it can be effective (and funny, I admit) to 'sneak up' to a target, jump up and surprise the other player or to deal blows with the gauntlet from your crouching position. As a bit of a noob player, my first reaction would be to fire straight in front, which is a waste of ammo and by the time I've realized someone's kicking me from down below, I'm already dead. Woops.
Answer: Crouching is good, for example, when sitting with gauntlet close to a teleport exit. One common technique is to make tens of frags when playing FFA on Asylum by taking Quad Damage and meeting all players coming from teleport with a gauntlet. For most of them this is an instant kill (150 damage in one hit) and crouching makes you a bit less visible from other parts of the map.

Is crouching in Quake Live useful?


how can i create the customize image with hadoop installation for openstack?

Question: I have used ubuntu builder to make iso image but it works only vmware .The image is not working on openstack. can you please help for make image for openstack with hadoop installation?
Answer: I'd start with a clean Ubuntu server instance, install Hadoop in it and see if I can make a snapshot from it and easily instantiate new ones (maybe write a script for the changes if it's not too hard).
If you want something automatic, you can try installing Juju and hook it up to OpenStack as a provider - it has Hadoop charms. Also, this question might be of interest to you.


What is the point of a Gantt Chart, and will it help me?

Question: My (non-technical) colleague has threatened me with a Gantt chart for a new project that we are currently planning.  What is this likely to provide for us, and will it be a helpful tool?
Comment: He *threatened* you with the chart? I'd call the police.
Comment: When someone threatens you with a Gantt Chart its well advised to block and counter attack with a Pie Chart -> To his face...
Comment: @Darknight no! pie charts are weak against gantt charts -- what this man needs is a logarithmically graduated histogram!
Comment: @bjarkef: Maybe he threatened to force him into keeping it up to date. To the OP: It's a way to write down and keep track of guesswork - that's all it is.
Comment: @EpsilonVector I think that might be considered unprofessional.
Comment: How do you "threaten" someone with a Gantt chart? Did he want to smack you in the head with his chart?
Comment: @bjarkef - Roll it up in a cylinder and bash someone with it ... it can be pretty effective/painful :)
Comment: I don't mean to hate but the comments are way better answers than the answers.
Answer: As Wikipedia says it Gannt chart is a type of a bar chart (more often a "line type") that helps with project planning. It is often drawn manually on the wall on a big (really big) piece of paper, since it is easily modified in that format.

It is a very simple type of planning tool; you can produce it in Excel or some equivalent; and rather effective, as long as the time required for certain phases of project can be roughly estimated. If there is a delay - no problem - one line get lengtened, the others stay the same and you have a new end-of-project-date.
Overlapping phases (time-wise) are easily seen on it, as easily as dependencies of starting one phase relying on the end of another.
'tis all there is to it really.
Of course, the problem with the Gannt (or the "time chart" as it is usually called in my part of the world) is that, that at the beginning of a project you have it all drawn up nicely on the wall, feeling enthusiastic and happy, ... then one delay occurs, and you change it on the chart, and you're still felling happy ... then another delay occurs, you draw it up again, and you're still feeling pretty good ... 100x delays occur ... you're feeling like _______ (censored).
Meaning, it is only a good project planning tool if you're actually sticking to those little deadlines. So stop wasting time in here and get to work!
Comment: And presumably if you delay too long, you could run out of wall.
Comment: @Allison, that's why the world is round...
Comment: @Alison - That too is a risk :-)) LOL
Comment: What are you talking about?  Managers don't change the chart, they just keep forcing you to promise that you'll make up the time, making you work 70 or 80 hour weeks!  :)  It saves paper that way...
Comment: @Scott Whitlock - :-)))) Hehehe
Comment: As long as you see the Gantt Chart as "this is what the current estimate looks like and the order in which we intend to do things" instead of a "this is how the project will progress", then it's a useful visual aid. Kinda like UML these days (few people actually _design_ software using it, they just try to understand the software from looking at generated diagrams).
Answer: A well-produced and maintained Gantt chart can be a great tool.  The main benefits are showing which tasks depend on other tasks, predicting how the project can be affected by delays, and highlighting wasted hours because you were waiting on something else.
Comment: Sounds very useful.  Are they standard where you work?
Comment: Yes, though only at the managerial level.  Our PMs all have MSProject and use it to track large-scale tasks.  This works ok since at the lower (individual task) levels, the status changes too rapidly to track effectively.  But we can tell when the QA work is gooing to be delayed because the development work is taking longer than expected.
Comment: The dependency map is by far the most useful part.  I sometimes make them without durations (or all the durations set to the default) just to get a graphical representation of what the bottlenecks are / are likely to be.
Comment: +1, and I think it's also useful to see which tasks are *not that critical* yet, so you can focus on beating other horses
Comment: ...and if you're not the bottleneck, it can be an invaluable tool for THE BLAME GAME!
Comment: This is how I use these charts as a personal tool, not so much to schedule but to force me into thinking of dependencies and to lay out an order of work.  Later I fill in the time used and from that my prediction gets better on future projects. +1
Answer: I have successfully used Gantt charts in the past for software project management. I have also seen people abandon them in frustration.
Any project management tool is useful only if it's answering questions that somebody is actually asking. In my case, I was continually asked two questions, and my Gantt chart could answer it:

My Manager: When will the software be
in a shippable state?
A Developer:
I've finished the task you had
assigned me. What task are you
assigning me now?

So what factors are required for a Gantt chart to be useful?
Multiple team members
That should be obvious. If there's only one team member, then all you need is a list of tasks in one column. You're only going to do them one after another.
Knowledge of what the tasks are
This seems like another obvious statement, but you'd be surprised how many software projects are not well defined enough to be able to divided into tasks. You'll actually need an upfront specification, and some degree of upfront design. In some of the agile/extreme methodologies you couldn't use a Gantt chart, because you don't know what tasks will be in the subsequent 3-week iteration.
Time and Motivation to Maintain the Chart
Somebody HAS to put the time in to maintain the thing. Too often, somebody spends days making up a detailed Gantt chart, then neglects it. Maybe he'll get it out a month later, laugh nervously, and throw it away, never to talk about it again.
Once you have the tasks and best estimates, you put them on the chart. And when the first task has been completed, you have to mark that on the chart and then jiggle all of the other tasks around to compensate for the fact your estimate was wrong. And two days later you do it again. And then again, another two days later. And of course, when it turns out you forgot something or a defect appears, you have to put the new tasks on the chart.
That might sound like a significant ongoing time commitment, and you're right. Where does the motivation to do this come from?
Somebody actually cares about the results
The times that I have used a Gantt chart successfully was where there were weekly project management meetings. The manager would go around the room asking each team leader to state when their project would be delivered. If a project was running behind then resources would be reallocated. For the first two meetings I would stammer that I didn't really know when it would be delivered, and would come up with a vague "in three months". The embarrassment of this made me change my strategy, and make damn well sure I had a Gantt chart that was up-to-date and accurate before each meeting.
As a side effect, this made my project better organised and more efficient, and my team members more motivated.
Answer: No single invention deserves more credit for making project planning as unpopular as it is today than Tracking Gantts. Tracking Gantts should not only be considered harmful - they should be considered evil. Here's why.
Reason #1: Their motivation
Tracking Gantts let you see, for each step of your plan, how long you thought it's going to take and how long it's actually taking. You get to know, every day and in status meeting, that phase X was supposed to start by March, but it's clearly not going to get started until May.
Awesome.
You already knew, when you did initial planning, that the plan is going to have to change as the project progresses. New information comes to light. People and resources are unpredictable, etc. So why is it important to constantly be reminded, in every status meeting, how poorly your early predictions are fairing in real life?
Reason #2: They force you to stick to the original plan
The very idea of tracking a project's Gantt chart means that instead of focusing on constantly adapting your work plan based on new information, you choose to stick to an outdated plan, just because it lets you point fingers and highlight the mis-predictions that were the inevitable result of the huge amount of uncertainty that the early planning phase of the project entailed. After all, you can't track the Gantt if you allow the plan to change radically, right? It has to have the same general shape and be comprised of the same steps, otherwise there's nothing to track...
Boneheaded sticking to plans is the number-one reason why "Waterfall" is actually considered a pejorative term these days. Planning ahead is confused with sticking to the original plan.
Reason #3: They teach you nothing
It's not like the delay in this project is actually going to change the way you plan the next project, unless the projects you're planning are predictably similar and repetitive. After all, that's what Gantts were initially used for - planning work in factory production lines, where tasks are very well defined and their duration is extremely predictable.
The value that tracking adds to a software development Gantt chart is zero. Arguably even less than zero. Not only are past estimations irrelevant for new projects, the illusion that you can actually improve your estimation ability over time by retrospection is dangerous. Sure, a CS student might really not know that integration takes lots of time in real life. But anyone that's been involved in more than two projects in their lifetime is already well aware of the usual suspects for delayed projects. The real reason projects are delayed is not some mathematical error factor that must be applied to estimations in general - it is the inherent uncertainty that comes with doing something for the first time and not knowing exactly how it's going to pan out.
There are actually project management systems out there that try to attack the problem from this misguided angle. They measure your predictions vs. actual performance and try to correct your overall estimation using statistical analysis. As if "Danny always underestimates everything by 14.3%" is ever the case. Danny isn't stupid, and to assume that the error of his predictions is predictable is indeed idiotic. It confuses the primitive "cure" - adding factors to your estimation - with the cause of the problem. Your estimation isn't inaccurate because it wasn't multiplied by the "correct" factor. Your plan is simply incomplete; and every plan is incomplete in its own way.
Reason #4: They focus your attention on the wrong things
Instead of being focused on what needs to get done to deliver on time, you're now focused on justifying your inaccurate predictions. Instead of focusing on planning in more detail and adapting your plan to new information, you're rehashing an outdated plan. Projects are seldom delayed because the work-plan's parts were incorrectly estimated. They're delayed because a crap-load of things were simply left out of the original plan. Tracking Gantts make this even worse, because what sort of motivation do you have to insert more detail into your plan if it's all just going to wind up highlighted as a poor estimations in every status meeting? They make you stick to large, track-able chunks of work in your Gantt chart. Instead of letting you focus on adaptation and getting on the right track, they make you reexamine irrelevant decisions that were made when less information was available.
There's also the problem of not having good enough tools to manage sufficiently elaborate plans. You have a much better chance at constructing a good initial plan (and estimation) if your tools allow you to expose all those frequently neglected steps along the way. Traditional Gantts are low-resolution beasts that are rightfully seen by developers as caricatures of the reality of project management. What's needed is a tool that makes it easy to add as much information as possible to the work plan at the earliest stage, and then make it just as easy to adapt your plan as the fog of uncertainty slowly fades away from over your project. The last thing you need is incessant low-resolution reminders of your inaccurate past predictions. Tracking Gantts are good for pointing fingers and covering asses, not for getting things done.
Comment: I think we need to clarify that you are focussing on "Tracking Gantts", not Gantt charts in general. I use gantt charts in some cases. But like you, I see no benefit in using the tracking features. When a new task comes up that you didn't think of, incorporate it in the gantt chart. Your adjusted gantt chart is now the plan. Yes, it's slightly different from last week's plan, but nobody should be surprised. If management are interpreting your initial estimates as commitments, then using this to bully you, you have a problem beyond gantt controls. +1 anyway - you make some good points.
Comment: Originally posted on my blog, but I thought I'd share it in full here. http://blog.gigantt.com/2010/12/tracking-gantts.html
Answer: Gantt chart software allows complex inter dependencies to be analysed and to predict the effects of overruns and delays.
However, for most software projects, there are few inter dependencies and external inputs, so the key to prediction is knowing what the right multiplier to use when the software team say it will take 3 weeks.
Comment: Yeah, for short projects, this is true. Heh.
Answer: As others have said a gantt chart (commonly informally referred to as a project plan) is a way of mapping tasks and the interdependencies between those tasks, the aim being to establish the minimum total elapsed time for a project.
From a management perspective the key output is the identification of the critical path, that is the list of tasks which if they are delayed then the project is delayed.
A very simple example - say two programmers are working on a project with three tasks (code module A taking one programmer 10 days, code module B taking one programmer 5 days, then integrate a and b taking both programmers 2 days).  The first two tasks (coding modules A and B) will be worked on in parallel and the aim is to complete all three tasks and thus the project it all in 12 days.
In this case the critical path is coding module A then integration testing.  The coding of module B can actually start 5 days late (or over run by five days) with no impact as even if it did finish on time, coding module A is going to take that much longer.  On the other hand if coding module A or the integration testing slips by any time at all, the whole project will slip.
Knowing this sort of thing helps you understand how to deploy resources and whether a delay to a particular task is likely to impact the whole project.
Are they useful?  Obviously yes, but with one significant caveat: only so long as the information that goes into them is good - that is:

the task list is complete
the estimates are accurate
the dependencies between tasks are comprehensive and
the resources representative of the team and correctly mapped to the task.

And from there the team has to work to the chart and carry out the tasks in the right order (no doing something that's more interesting that the assigned task as that will potentially delay something / someone else down the line).
If you do all that then yes, then it can really help you but the work does have to be put in up front to ensure it's accurate and realistic.
Answer: I LOVE Gantt charts and if there were better software choices for the Mac to create them, I'd use them all the time.
Getting to see the dependencies is huge.  "If we don't get the data backfilling part of the project done, then construction on the whatsit enhancements can't start."
Comment: if there were better software choices for the Mac... I'd say there are better choices than a Mac ;-)
Answer: If your project is a software development project then a gantt chart won't be very helpful and will mostly be a waste of time. They aren't designed for the fluid nature of software development, ie.

Tasks aren't usually order dependent. They can be done in any order.
The order of the tasks can alter the time required to complete the task.
Tasks can spawn other tasks, eg bugs

The upshot is you will spend more time updating the plan than doing the work.
Just manage your requirements and everything else will take care of itself.
YMMV


Arduino Bootloader

Question: I am very new to embedded world. I had been till now working only on S/W
Can anyone please explain me the use of the Arduino Bootloader? I want Arduino to perform some simple mathematics using some additional components that have to be put in to the chip.
Do I necessarily need a bootloader?
Answer: The Arduino is basically just an Atmel AVR microcontroller, with just enough support electronics to allow it to operate. The AVR has built-in flash to allow it to keep programs with the power off, but to program an AVR chip directly you need a tool like the STK-500 to do the job. The Arduino overcomes this by also having a small USB interface on the board, and the Arduino boot-loader code already on the chip. This allows the PC side application to transfer your programs to the device, and in essence, have it flash itself.
So, bottom line, if you get an Arduino, the boot-loader is already there, and does its job automatically. You code your program on the PC, press the 'upload' button on the IDE, and within a few moments your program is running on the Arduino. The boot-loader does its job completely transparently.
fwiw, I personally have an Arduino 2009, and an STK-500 and can do on-the-metal programming on AVRs, but have found no need to bypass the Arduino's bootloader.
Comment: I'd love to see more info about using an Arduino to program an AVR.
Comment: http://news.jeelabs.org/2010/07/02/fixing-a-faulty-atmega-arduino/
Comment: @Greg there is actually an arduino supported sketch for the duemilanove to flash the bootloader onto a bare atmega328. Obviously, this functionality could be extended to flash any program onto a bare atmega328. You do not need an ISP connector. Essentially you turn your arduino micro into an ISP.
Answer: The Arduino needs a bootloader in order to program your sketches over serial/USB. Without it you need an AVR In-System-Programmer (ISP) to program the flash memory in the AVR chip directly.
If you buy an Arduino, it'll come with the bootloader already burnt into the AVR chip. You only need to worry about it if you're building your own board.
This should help:
I don't get the Arduino concept
Answer: I'll give a slightly more theoretical answer; the other answers are quite good from a practical perspective. A bootloader is code that resides in a special segment of flash memory. Code that resides in that segment is allowed to execute Self-Programming Instructions, making it possible to modify flash memory (i.e. where user code resides) without a conventional programmer (i.e. In-System Programming ISP or High-Voltage Programming HVP) like the STK500 or AVRISP mkII.
In principle, the UART Recieve Data Interrupt Service Routine (ISR) makes a function call into the bootloader code that copies the program image being sent serially into the user program space in flash memory. At startup, whatever program is on the chip starts running, but if appropriately formed serial data is received early on, the AVR goes into a sort of self-programming mode. There is some logic in the UART ISR that only defers to the bootloader code for a short period of time during startup. The details are a bit more complicated than that, but that's the basic idea.
The beauty of this is that you can buy an Arduino, and nothing else, download the free Integrated Development Environment (IDE), and start writing Arduino Sketches (programs), and download them onto the AVR just like that, over USB no less thanks to the fancy little FTDI IC chip that's integrated into the Arduino board.

Arduino Bootloader


Is there a way to check how I ended a mission in Mass Effect 2?

Question: I beat Mass Effect 2 a while ago and I can't remember how Tali's loyalty mission ended. The journal entry says something like "Tali is grateful that her father was not exposed, but she is happy to leave the machinations of the Flotilla to return back to the Normandy." I can't tell if she was cleared of charges or convicted. Any help?
Answer: The journal entry is pretty much all there is, and as long as you didn't expose her father, the text is the same whether you did it by talking your way out of it, or by getting her exiled. As far as I can tell, there are also no emails or repeatable dialogue options that reveal whether she was exiled or not.
The only way I can think of is to check your Omni Tool Upgrades. If Tali was found innocent, you will have received an additional +10% Tech Damage upgrade, so if you have all 5 (6 if you have the Kasumi DLC), you'll know she wasn't exiled. If you don't, you can't really tell, since you may just have missed one.


How to copyright an image which will be posted on a tumblr blog?

Question: I am using tumblr from last 2-3 years.
Now I want to use Tumblr for blogging photos. But I want my photos to be copyrighted. Is there any way to copyright them so that I can post them on tumblr??
What kind of copyright options do I have?
Also I would like to know if there is any way to copyright all types of content in tumblr?
Comment: Which country do you live in?
Comment: @iglvzx I live in India
Answer: Unless you live in one of the handful of countries that are not signatories to the Berne Convention, I can reliably state that you automatically get copyright protection on your works when you create them.
Enforcing that right can be a lot trickier and some countries give you extra privileges if you explicitly register your copyright with the government, but having your works "copyrighted" is automatic.
If you mean something else by "want my photos to be copyrighted", you'll have to elaborate. (Displaying copyright notices? Licensed under terms other than "All rights reserved"? Something else?)
UPDATE:
If you took a photo, you can do whatever you want. Every way is "legal". Copyright is about letting you control what other people can do with your creations.
Watermarks are one way to ensure attribution for your work, but if you actually want people to reblog them, stick to something small and in a corner or along the bottom. Big watermarks are annoying and, with so many other people using Tumblr, if you're annoying, people will just look elsewhere for their pics.
Another method that you can use in addition or instead, if your photo software supports it, is to embed XMP metadata into the photo, which will let other programs automatically find and use the authorship information. (Think of it as similar to the ID3 title/artist/album information in MP3s, but for pictures instead. You've probably run into at least one MP3 which showed up as "Untitled" or "Artist - Track 6" in your playlist because it had no ID3 metadata.)
As for Creative Commons licenses, they're a way to pre-emptively grant permissions that you're comfortable with, so people don't have to ask you for every little thing. (This makes people more comfortable in using and sharing your photos, limits the harm if people ever find themselves unable to contact you, and may make some people more willing to stay within the rules you set by showing them that you're a reasonable person who deserves some respect.)
If you follow the instructions in the Creative Commons licensing tool properly, it'll also make sure that your photos show up when people search Google for only images with creative commons licenses.
Tumblr doesn't appear to have any special functionality for automatic watermarking or Creative Commons license marking the way sites like deviantART or Flickr do, so all I can suggest that's actually on-topic for webapps.stackexchange.com is that, if you want to put your entire Tumblr blog under the same license, you can follow the instructions Creative Commons offers at http://wiki.creativecommons.org/Blog/Publish#Tumblr
Comment: ok. thanks a lot!! I have seen some tumblr blogs where photos with a water mark are posted. Is this the legal way so that even if some people reblog their photos, it still has the author's name or signature. Is there any other alternative to this? What about creative commons?? How can I use it?


Best Way to Build & Design Buttons, Icons for Mobile application

Question: Which is the best Way to Build & Design Buttons, Icons for Mobile application of Android and IOS platform.
Answer: I'd say coming up with several designs that follow basic GUI guidelines and testing them on the devices is a good start. I also think trying to keep them in one continuous style helps giving an overall complete look. Keep in mind they have to work in varying resolutions. So either find a good balance between complexity and simplicity or make different versions for different resolutions.
For both systems there is a lot of documentation on this too:
Android Guidelines
iOS Guidlines
Other than that, I am not exactly sure what "best way" you are asking for.
Answer: Actually depends on your ability. If you work with Adobe Photoshop or CorelDraw With a general understanding of software, you can be a Icon Designer. Just in about IOS maybe It may be a little hard, because The operating system has limitations. for example XCODE in MAC has some simple Icons and you can use them. In generally I think Adobe Photoshop is a very useful design program for all of code writers and programmer.


How does the "risk-neutral pricing framework" work?

Question: I've struggled for a long time to understand this - What is this?  And how does it affect you?
Yes I mean risk neutral pricing - Wilmott Forums was not clear about that.
Comment: You can have a look at my [blog post](http://blog.smaga.ch/introduction-to-risk-neutral-pricing-theory/) which helped a few people grasp the concept.
Comment: Can you please elaborate on your question a little?  "how does it affect you?"  Also, maybe provide a link or two to relevant resources?
Comment: @ChloeRadshaw: You can accept one of the answers if you are satisfied by it :-)
Comment: You still did not accept one of the answers, although this question is many years old - is there anything still unclear?
Answer: I assume you mean risk neutral pricing? Think of it this way (beware, oversimplification ahead ;-)
You want to price a derivative on gold, a gold certificate. The product just pays the current price of an ounce in $.
Now, how would you price it? Would you think about your risk preferences? No, you won't, you would just take the current gold price and perhaps add some spread. Therefore the risk preferences did not matter (=risk neutrality) because this product is derived (= derivative) from an underlying product (=underlying).
This is because all of the different risk preferences of the market participants is already included in the price of the underlying and the derivative can be hedged with the underlying continuously (at least this is what is often taken for granted). As soon as the price of the gold certificate diverges from the original price a shrewd trader would just buy/sell the underlying and sell/buy the certificate to pocket a risk free profit - and the price will soon come back again...
So, you see, the basic concept of risk neutrality is quite natural and easy to grasp. Of course, the devil is in the details... but that is another story.
See also my answer to a similar question here: Why Drifts are not in the Black Scholes Formula
Comment: @ChloeRadshaw: It is in fact all connected: From the law of one price follows risk neutral pricing - the reason is the possibility of hedging.
Comment: I like the explaination +1
Comment: So risk neutral pricing means pricing an instrument which can be immediately hedged?  Is nt that the same as no arbitrage law?
Comment: This answer does not mention the change of measure from the real-world probability measure to the risk-neutral one, which I think is needed in order to understand the (first) fundamental theorem of asset pricing [ http://en.wikipedia.org/wiki/Fundamental_theorem_of_asset_pricing ].
Comment: @WilliamS.Wong: The question was about risk-neutral pricing in general, i.e. understanding the concept and getting an intuition. Yet, please feel free to give another answer :-)
Comment: Is it fair to conclude that risk-neutral pricing can only be used on derivatives?
Answer: We bet on a fair coin toss -- heads you get $\$100$, tails you get $\$0$. So the expected value is $\$50$. But it is unlikely that you'll pay $\$50$ to play this game because most people are risk averse. If you were risk neutral, then you WOULD pay $\$50$ for an expected value of $\$50$ for an expected net payoff of $\$0$. A risk neutral player will accept risk and play games with expected net payoffs of zero. Or equivalently, a risk neutral player doesn't need a positive expected net payoff to accept risk.
Let's say that you would pay $\$25$ to play this game. That means if you were risk-neutral, that you'd be assigning probabilities of 1/4 to heads and 3/4 to tails for an expected value of $\$25$ and an expected net payoff of $\$0$.
So if we can convert from the risk probability measure $(1/2, 1/2)$ to a risk neutral probability measure $(1/4, 3/4)$, then we can price this asset with a simple expectation.
So if you can find the risk neutral measure for an asset based on a set of outcomes, then you can use this measure to easily price other assets as an expected value.
Comment: @BCLC prices are determined by the market. The risk-neutral measure is artificially configured so that the expectation of a contingent claim under it can match its market price. Theoretically, converting from the physical measure $\Bbb P$ to the risk-neutral measure $\Bbb Q$ involves Girsanov theorem, where you add a drift $\lambda_tdt$ to the standard BM dynamics $dW_t^{\Bbb P}$ to get the new standard BM $dW_t^{\Bbb Q}$, and $\lambda_t$ is determined (estimated) by available market price data.
Comment: Why is it that your example has some price and then we deduce risk-neutral probabilities? I was expecting we have some risk-neutral probabilities and then compute the price.
Answer: Suppose that you and other bettors participate in a lottery with $N$ possible outcomes; event will occur with probability $\pi_n$. There are $N$ basic contracts available for purchase. Contract $n$ costs $p_n$ and entitles you to one dollar if outcome $n$ occurs, zero otherwise.
Now, imagine that you have a contingent claim that pays a complex payoff based on the outcome, say $f(n)$. The expected value of the payoff is
$$E(f(n))=\sum_n \pi_n f(n) =E(f)$$
Now, consider a portfolio of $f(1)$ units of basic contract $1$, $f(2)$ units of basic contract $2$, etc. This portfolio has exactly the same random payoff as the contingent claim. Because of the law of one price, it must have the same price as the contingent claim. Hence, the contingent claim has price equal to
$$\text{price}(f)=\sum_n p_n f(n)$$
Define $r= 1/(\sum_{i=1}^N  p_i)$ and set $\tilde p_n :=  r p_n$, which is a probability measure, and you can rewrite
$$\text{price}(f)=r^{-1} \sum_n \tilde p_n f(n)=r^{-1} E^*(f)$$
So the risk-neutral probabilities are essentially the normalized prices of "state-contingent claims", i.e., outcome-specific bets. And the price of any claim is the discounted expectation according to this probability distribution. $r$ is easy to identify: if the contingent claim is 1 dollar for any outcome, then it's price is the discounted value of a dollar using the risk-free interest rate. Hence $r$ is the risk-free interest rate.
Where do these prices come from? There are three ways to think about price determination:

They are determined by a
non-arbitrage condition, where no
bettor can make something for
nothing almost surely;
They are determined by an
equilibrium condition, where all
bettors optimize their utility;
They are determined by a
single-agent utility optimization
problem.

All conditions imply that the prices are strictly positive. For more information, Duffie's Dynamic Asset Pricing is still the standard reference.
This basic intuition behind this framework goes back 35 years to Cox-Rubinstein. Harrison-Kreps extended the result, and since then it has further extended. The most general forms to useless level of technicality are by Delbaen and Schachermayer.
Comment: ".. then it's price is the discounted value of a dollar using the risk-free interest rate. Hence r is the risk-free interest rate." -- shall be "... then it's price is the discounted value of a dollar using the risk-free interest rate. Hence $r = 1 + R$, where $R$ is the risk-free interest rate."
Answer: The risk-netural measure has a massively important property which is worth making very clear:

The price of any trade is equal to the expectation of the trade's winnings and losses under the risk-neutral measure.

This property gives us a scheme for pricing derivatives:

take a collection of prices of trades that exist in the market (eg swap rates, bond prices, swaption prices, cap/floor prices),
back out the set of risk-neutral probabilities that these prices imply,
calculate the expectation of the derivative trade's payoff under these risk-neutral proabilities,
that is the price of the derivative.

The risk-neutral measure is in some sense the flip-side of the concept of risk premium.
Without even getting mixed up with stock and bond prices and suchlike, we can get a good sense of the risk-premium concept at work in a simple betting game.
The classic example, a game of coin tossing:

a player hands over some money, say £X, to play,
the host tosses an unbiased coin,
if it comes up heads then the player is given £2,
but if it comes up tails then nothing is given back.

A textbook on probability will tell you that the price of £1 per go is fair for this game because the concept of fair is defined in probability textbooks to mean that the price paid should equal the value of the expected winnings. Clearly it does for this example.
But let's get savvy, step back from the theory, and ask how much would different players be prepared to pay for this game. Consider two different players:

person A that has £1.50 in their pocket but is under pressure from a traffic warden to pay £2 for a parking ticket (and nothing less than £2 will do),
person B that has £10 in their pocket and doesn't really need anything more than that.

Don't you think you could convince person A to pay up to their whole £1.50 for this game? Person B might be a harder sell, but perhaps they'd come around if we charged something like 50p a go and advertised the game as 'potential 4 times returns on your investment'?
The important point is that the theoretical fair price may well be £1 for this game, but the actual price at which we sell the game may be something different since it will depend on the circumstances of the players we are selling it to.
The difference between the actual and theoretical price is called the risk premium. Throwing in a bit of market language, we can write this as:

the risk premium is the amount of premium (or discount) that needs to be added to the theoretical fair price in order to match the actual price of the trade in the market.

Remark: The risk-neutral measure is risk-neutral because in this alternative reality the price paid by player A for the game contains no risk premium — the price is exactly equal to the value of the expected winnings of the game.
I have written a little bit more on this in my blog if you want to go see.
Comment: Don't just post a link to your blog (especially since this particular link goes to a sign-in page). Either give a real answer here or I'm going to assume you're spamming us.
Comment: Removed the link to my blog. Then noticed vonjd's comment (had skimmed over it somehow) and put the link back -- to be fair there is quite a bit more there in my post than I would wish to copy over into this answer, so a link seems reasonable.
Comment: Fair comments. I have now fixed the link and filled out the body of my answer.
Comment: @vonjd Good point about Meta. It turns out [this has been asked before](http://meta.stackexchange.com/q/15432/154119). Marc says that it's ok for occasional use, not as a regular occurrence. My spam bells went off when both of Robert's original answers were simply links back to his blog. To be honest, I thought it was just spam until I noticed that he has a legitimate email address. The moderators have to delete spam posts on a semi-regular basis, and Robert's answers were indistinguishable from those.
Comment: I think this might just be a bad link - the right one might be this one? http://fermatslastspreadsheet.wordpress.com/2012/01/24/what-is-the-risk-neutral-measure/
Comment: @Robert This is better, though if you look around you'll notice that nobody else posts a link to his personal blog. Every answer is either self-contained or links to an established source (like a Wikipedia article, a book on Amazon, or another post within Stack Exchange). Please edit your answer again to remove the link to your personal blog.
Comment: @chrisaycock: I think the form in which the article is now is fine. When links to other resources are ok links to your own resources are ok too (provided they add some value which seems to be the case here). If you don't agree perhaps we should raise this on meta, what do you think?
Answer: A market is said to be complete if any contingent claim can be replicated by an admissible (i.e. with value process bounded from below) self-financing (i.e. all gains and losses exactly offset each other) trading strategy, a so-called replicating strategy. This strategy being constructed from primary securities - the market prices of which are unique - it must be that its price is identical to everyone, and the strategy is therefore independent of any assumptions on risk aversion. Any discrepancy between the replicating strategy's price and its underlying primary securities would be wiped out by arbitrage trades by market participants, regardless of their risk preferences.
Now, suppose you want to price a contingent claim, e.g. a European option on an equity security. Assuming the market is complete, the payoff of this security can be perfectly replicated using existing securities. Again, by the same arguments as above, the market price of the option and of the replicating strategy must be exactly the same under a no-arbitrage condition, regardless of risk preferences. Therefore, neither a positive nor a negative risk premium can be embedded into the equilibrium market price of the option, or equivalently of the replicating strategy (actually, a sort of "aggregate" risk premium is already included in the prices of the replicating strategy's primary securities, but no further risk premium is added when pricing the contingent claim).
We have shown that if the market has no arbitrage opportunities and is complete, then it must be that the option's market price is exactly equal to that of the replicating strategy, and that this price is in fact unique. This is essentially what the (Second) Fundamental Theorem of Asset Pricing (FTAP) says. Since the replicating strategy does not depend on any assumptions concerning risk preferences, it does not matter what assumptions are made on the risk preferences of the market participants. Therefore, the price in the real-world market (where risk-averse, risk-neutral and risk-seeking participants meet) must equal that in a risk-neutral market. Since it is much more convenient (and mathematically powerful, e.g. martingale theory) to work in a risk-neutral world, this is the standard pricing approach used in mathematical finance.
Answer: I like this point of view on risk-neutral pricing:
risk-neutral probability $q$ is such a probability that the expected possible price of the option at $t=T$ calculated with this probability and then discounted gives you today price at $t=t_0$
It is derived from today price under the assumption that all the time holding portfolio of option (buy) and instrument (sell) you are delta hedged, so its value is known and the same in each case (rise, fall).
Other nice view is:
future price of the option (expected with risk-free rate) is equal to its expected value, i.e if today price is $V$ and option price tomorrow might be $V^+$or $V^-$ and risk-free rate is $r$ then you can retrieve $q$ from this equation:
$(1+rdt)V=qV^++(1-q)V^-$
Answer: I learned something about decision sciences, stochastic processes and mathematical modeling in college before I learned something about quantitative finance, so I had struggled to grasp the concept which is so familiar and yet so alien. Here is my two bits. I might overlap with some of the previous answers at some parts, but the approach is different.
Before explaining risk neutral or martingale measure framework we need to clarify something. The objective of option pricing is to find a fair price. The definition of the fair price is the value which both side of the contract (long and short) should make the exact amount of money as if they were agreeing on a deposit with a fixed amount of interest rate (called risk-free rate with common abbreviation r). Plus some of the fine print; no friction (no taxes, no spread, borrow and lend at the same rate r).
To make things even easier with an example assume r is 0 and we live in a perfectly deterministic world. The price of asset A is 100 today and will be 120 in three months. Finally assume that I can only do a transaction (buy or sell the asset itself) after three months. Call it a rigged game if you like. If I were to write a European Call option contract with strike price 100 and maturity three months the fair price of the contract would be 20. Because in three months I will need to sell the asset for 100 to the counterparty (the person who bought the contract from me) and I have to buy it from the market for 120.
There we go. The buyer gave me 20 at t=0 and I bought the asset from the market for 120 and gave it to the buyer for 100. Then the buyer sold the asset to the market for 120. I have nothing in my hands and the buyer got his 20 back. In other words, we only killed time by doing a bunch of transactions and we are on square one. This is called equilibrium.
Of course real world is harsher. First of all real world is quite complex and stochastic (at least to us). You can sell and buy assets most of the time. And risk free rate can be different than 0.
Risk neutral pricing framework is only a way to estimate the fair price, albeit a popular one. The basic trick is to replace the drift with the risk-free rate. Then you discount your prediction on the asset by the risk free rate. The expected value of your outcome is the same as your current position. In other words, on average you don't get an extra dime than putting your money into a deposit or a solid bond.
You can also see that in the classical CAPM model. They essentially say 'No matter how or what you trade, on average you can't make more or less than the risk free rate.' This is the equilibrium state. If you are familiar with the concept it is similar to a steady-state markov chain. You can also relate with the common belief 'You can't beat the market (or index).'
Complete markets assumption is the core part of the option pricing (at least the distinguished BS pricing). It simply says (by the fundamental theorems of asset pricing - Shreve's book) the market is arbitrage-free (otherwise it would be trivial and there won't) and risk-neutral measure is unique. Oh, there can be more than one (enter the Levy processes or GARCH pricing), it is unsurprisingly called incomplete markets.
All those paragraphs and I haven't mentioned hedging yet. Recall the assumption you can't trade before three months. If you relax that assumption the price of the option drops to zero. Because since I know it will be 120 in three months and risk free rate is 0, I can immediately buy the asset for 100 and hedge myself completely. If I can sell the option for more than 0 to a sucker I make extra money (in other words arbitrage).
Now if we relax the deterministic part, in a complete market you can do the hedging by buying and selling the underlying asset continuously as the price of the underlying changes. It is also called delta hedging. The result will be the same though, no extra money to neither side on average.
"On average" or "expectation" are fundamental concepts that you need to set straight. I especially like Chevalier de Mere example or casino example ('House always wins') in such cases.
If you want me to speak more enigmatic so my words ring more true I quote Wikipedia:

"In economics, a complete market (or complete system of markets) is
  one in which the complete set of possible gambles on future
  states-of-the-world can be constructed with existing assets without
  friction."

Some footnotes.
Risk neutrality in decision sciences indicates the indifference between two games (or lotteries); one pays a fixed amount say 10, and the other indicates a win (more than 10 with probability p<1) and a loss (less than 10 wp 1-p) but the expected value of the game is the same amount of the risk free payoff 10. Risk seekers take the bet, risk averse people take the fixed amount.
Option pricing, portfolio optimization, risk management and similar areas all have the same objective, modeling and predicting the future value of an asset. But they usually differ in methodology. There are some bridges though, see Gerber and Shiu's paper on using an actuarial method called Esscher transform and come up with the BS model.
The popularity of the risk neutral pricing or complete markets comes from you don't need to think about the preferences (whether the agents are risk seeking or risk averse, so you have an 'objective' assessment).
Answer: I found that all of the answers under this post involves probability and randomness. In my humble opinion, risk neutral pricing does not have to involve randomness, and the notion comes so natural that we are applying it in our everyday life. So I would like to give an answer to simplify the concept of risk neutral pricing.
Think of your bank account. You have a 3-year term deposit that pays you \$5 at the end of every year and also pays back the principal amount of $100 at the end of the 3-year period. How would you price this asset?
Easy, right? We would discount the cash flows with risk-free rate because money in the bank is essentially risk-free (it's not actually risk-free, but we will talk about it later). Let's suppose we have chosen the yield of U.S. Treasury Bills as the risk-free rate. Assume that the 1-year Treasury is currently at 1.5%, 2-year Treasury at 2.0%, and 3-year at 2.5%. The present value (PV) of your bank account is, therefore, the PV of the first year's cash flow 5/(1+1.5%) + PV of the second year's cash flow 5/(1+2.0%)^2  + PV of the third year's cash flow (100+5)/(1+2.5%)^3.
Hold on for a second! But isn't the sum of these three numbers just the value of the Treasury Bills that you need to purchase in order to replicate the cash flows of your bank account? Yes! You would have to purchase 5/(1+1.5%)=\$4.9261 of Treasury Bills for replicating the first year's \$5, because it takes 1 year for \$4.9261 of 1-year Treasury Bills to grow to \$5 (this is just the definition of yield). Similarly, it takes 2 years for 5/(1+2.0%)^2 =\$4.8058 of 2-year Treasury Bills to grow to \$5 in order to replicate the second year's cashflow. And it takes 3 years for (100+5)/(1+2.5%)^3 =\$97.5029 of 3-year Treasury Bills to grow to $105 in order to replicate the third year's cashflow. Through no-arbitrage argument, the PV of your bank account has to be equal to the sum of PVs of the replicating Treasury assets. As a result, the PV of your bank account is \$4.9261 + \$4.8058 + \$97.5029, and we have just priced your bank account using the market pricing of Treasury Bills (yield is the market pricing of Treasury Bills).
This is called risk-neutral pricing! But you may ask what is the "risk" here? Well. If you think about it, your bank accounts and treasury bills are not actually risk-free. Of course, there is no credit risk in them, but there is still interest risk. In other words, when interest rates or yields rise, the price of your bank account or the Treasury Bills will fall. The further in the future the cash flow is, the higher this interest risk (you can try to add 1 percentage point to the discounting factor in each year's cash flow, and you will see that the third year's cash flow has the largest percentage drop).
What is more important, this interest rate risk has already been priced in the Treasury yields, and that is partially why you see that the longer treasuries have higher yields, because the investors require a larger compensation for higher interest rate risk (This is also why the yield curve is usually upward-sloping even the interest rate expectation is flat). Thus, when you price your bank account, you have already taken into consideration the interest rate risk inherent in your bank account. In other words, you have "risk neutralized" interest risk in your pricing!
See? The essence of risk neutral pricing is to price one asset through cash flow replication with other assets whose prices we already know. In doing so, we will be able to price in the risks using the market prices of these other assets, as the market has already priced in the risks with the prices that the market collectively believes as fair. Being able to replicate cash flows is massively important, as you can see that the argument in the bank account example will fall apart if you are not able to replicate your bank cash flows with Treasury Bills.
Note that our example does not involve any randomness, in contrast to what is being traditionally taught in the classroom. However, the same thought process holds when you are pricing an asset whose price is random (for example, a call option, as opposed to a bank account). You just need to find a portfolio of assets to replicate (or hedge) the cash flows of the call option, and the initial value of this portfolio (which consists of the underlying stock and cash) will be the fair price of call option through no arbitrage argument. The replication (or hedging) just needs to be dynamic in this case due to randomness. This is exactly what Black-Scholes is trying to do.


What errors would one learn from Eliezer Yudkowsky's introduction to quantum physics?

Question: Eliezer Yudkowsky wrote an introduction to quantum physics from a strictly realist standpoint.  However, he has no qualifications in the subject and it is not his specialty.  Does it paint an accurate picture overall? What mistaken ideas about QM might someone who read only this introduction come away with?
Answer: I realize I'm late to this discussion.  For whatever it's worth, I disagree in the strongest terms with Ron Maimon and Dmytry, when they criticize Yudkowsky for being "too conceptual."  As I see it, that's exactly what you should and must do if your goal is to explain QM to an audience of non-physicists!  Indeed, most popularizations of QM go off the rails precisely because they try to describe a huge array of weird phenomena that people were trying to make sense of in the years between 1900 and 1926, while burying or downplaying the single conceptual point that was eventually found to underlie all of those phenomena.
That point, of course, is that we have to replace probabilities (which are nonnegative real numbers) by amplitudes (which are complex numbers)---and that unlike probabilities, amplitudes can "interfere" and cancel each other out.  As demonstrated by any modern quantum information textbook, it's possible to explain almost all of what the typical non-physicist wants to know about QM -- e.g., what's entanglement? what's the Bell inequality? what are the arguments for and against Many-Worlds? -- while just talking about qubits, unitary transformations, and vectors of amplitudes, and never saying anything about the energy levels of hydrogen (or even particles and fields at all!).  Of course, once someone understands the mathematical framework of QM, they're then in a much better position to learn some of the physics built on top of that framework, should they want to.  But if you try to tell a layperson about tunneling, energy levels, wave/particle duality, etc. etc., before he or she even understands the concept of an amplitude vector, then the take-home message is simply going to be "anything is possible in the weird and wonderful world of QM!"
So I commend Yudkowsky for writing an entertaining series of posts (well, at least, I enjoyed them :) ) that explain QM from his personal, non-physicist perspective, and that actually get most of the technical stuff right.  I would criticize Yudkowsky, not for focusing on "dinner-party" topics, but for two other things:
(1) I think Yudkowsky's central argument---basically, that anyone who rejects Everett needs to have their head examined---is to put it mildly, a bit overstated. :)  I'll resist the temptation to elaborate, since this is really a discussion for another thread.
(2) In several posts, Yudkowsky gives indications that he doesn't really understand the concept of mixed states.  (For example, he writes about the No-Communication Theorem as something complicated and mysterious, which it's not from a density-matrix perspective.)  As I see it, this might be part of the reason why Yudkowsky sees anything besides Many-Worlds as insanity, and can't understand what (besides sheep-like conformity) would drive any knowledgeable physicist to any other point of view.  If I didn't know that in real life, people pretty much never encounter pure states, but only more general objects that (to paraphrase Jaynes) scramble together "subjective" probabilities and "objective" amplitudes into a single omelette, the view that quantum states are "states of knowledge" that "live in the mind, not in the world" would probably also strike me as meaningless nonsense.
Answer: I skimmed a majority of the articles, and there are no glaring errors that I could find, but there is an unnecessary verbosity which is best eliminated by reading a terser introduction to the Everett interpretation. The amount of text that is presented is not commensurate with the amount of insight.
The philosophical issues are discussed at great length, with references to Chalmers, but these issues are essentially ignorable, because Philosophers had it right originally 50 years ago when they were positivists. In positivism, you don't admit questions which do not have an impact on observation. So "is does my friend a soul, or is he a zombie?" is exactly the kind of question which is completely meaningless. The notion of zombie is fundamentally inconsistent, it is an abuse of language in the sense of Carnap.
The only reason philosophers use zombies is to make sure that their students do not discover positivism, since just by considering that a zombie makes sense, you are automatically engaging in positivistically meaningless discourse.
If you absorb the logical positivist's insights, as all physicists have done for at least a century, you don't have to bother with the first few posts at all. The sections on splitting and decoherence are basically correct, but again too verbose--- the basic idea is presented on Wikipedia in a few paragraphs, and in Everett's 1957 paper in a few pages. The verbosity is a problem, as the main problem is the "thin worlds stop existing" which is explained with a mysterious and not completely satisfactory gloss in the blog posts.
The problem with non-physicist sources is that they generally waste too much time on "profound" ideas, and spend too little time on actual calculations. A person should at least know how to solve the H-atom, and calculate the photon emission transition probabilities between a few levels. You should know how the entanglement in molecules or in He look like, at least qualitatively. You should learn Feynman's methods that work so well to organize condensed matter and high energy physics calculations.
Once you learn how to do the calculations, the profound ideas will take only a miniscule effort by comparison. To internalize the ideas required for the calculations require you to construct a mental lever to multiply your conceptual powers, as these ideas are like a heavy boat weighing thousands of tons. Once you construct the lever with enough power to lift the boat, and you drag the boat ashore over a period of months and years, the philosophical problems are like a dinky boulder, too heavy to lift with the bare hands, but trivially light compared to the ship. You use the same lever and lift the boulder with your pinky. It is trivial in comparison.
But it is not completely trivial to those who didn't spend enough time making a good lever. Instead of making longer and longer explanations to make the task achievable for the lever-less, one should explain how to build the lever.
I think that the presentation is essentially accurate, but too long to be useful.
Answer: Starting with his page 'Configurations and Amplitude' he describes a Mach-Zender interferometer (link, http://en.wikipedia.org/wiki/Mach%E2%80%93Zehnder_interferometer).
His formulation is,
starting phase = -1 + 0i
on hitting a mirror we multiply by i
For the straight path both photons hit two mirrors so we sum (-1 + 0i) * i * i, and (-1 + 0i) * i * i =  2(1 + 0i)
take the modulus, we get a number hence signal.
For the path that turns pi/2, we're hit reflected by either three mirrors or one mirror, sum (-1 + 0i) * i + (-1 + 0i) * i * i * i = 0
take the modulus hence no signal.
Unfortunately the traditional maths goes more like this,
We see a phase inversion, when we reflect at a surface with a higher refractive index.
The straight path, gives one reflection each by a normal mirror, therefore both paths have inverted phase, therefore no cancellation.
The pi/2 path gives either one reflection by a normal mirror, or three reflections, one from a normal mirror (phase shift), one from half silvered mirror at the front of the mirror (phase shift), one from a half silvered mirror at the back (no phase shift). Therefore one signal has the phase inverted once, one has it inverted twice. They interfere and no signal is produced.
Coincidentally this is the same answer as above.
To turn this into testable predictions, if you turn the first half silvered mirror around, under Eliezer Yudkowskys formation nothing would change, under the classical formulation the signal would move to the other detector.
Carrying out this experiment involves a fair number of practical difficulties (in particular this is an idealised experiment that currently is missing all the bits of glass required to compensate for refractive indices which would have to be moved appropriately, plus it's very important for the half silvered mirror surface to remain in exactly the same place). In the absence of an easy experimental verification I think it's reasonable to assume that the theory of optics as taught by every university physics course is probably right, and Eliezer is not.
Answer: I recommend to actually study physics if you want to learn physics. This kind of stuff is for dinner table talk, and still you are much better off reading popularizations written by physicists than by professional bloggers. I stopped at

The early scientists—you're going to laugh at this—thought that the
  silver mirror deflected the photon half the time, and let it through
  half the time.
Ha, ha!  As if the half-silvered mirror did different things on
  different occasions!  I want you to let go of this idea, because if
  you cling to what early scientists thought, you will become extremely
  confused.  The half-silvered mirror obeys the same rule every time.

The 'half silvered mirror' is a messy layer of metallic silver (think some crystalline structures) attached to a glass substrate, a couple wavelengths thick [actually I'm not sure how thick it has to be for silver], of varying thickness, with oxide stuck on it. It also absorbs some of the light, it has different delay for reflecting and transmitting [namely, half the wavelength for reflection, but that may just be the ideal case]. Followed by extra delay by the glass plane. The light of different polarization directions reflects to different extent. The interferometer set up in question has all the light going into one eye, or into other eye, if one of the paths warms up because you stand next to it, and increases in length by a half wavelength. Likewise if the pieces of glass are not of exactly equal thickness. What you actually see if you build this back in the day, is interference fringes, because the light that is going at an angle, does encounter different path length.
This is to give a little backgrounder on what this set up does do, which is very worthwhile to learn first before getting into quantum mechanics. What it does not do, is behave like a neat abstract system, where it is clear what is going on if only you are a rationalist and don't have biases.


games and rendered surfaces get slow after having computer on for some time

Question: I have an i5 2500K and nvidia 9600 GT with proprietary driver. For some reason, this set up on 12.04(and was same on 11.10) seems to work fine on boot up, but after about 30 mins of use, games and other accelerated surfaces start running at about 5fps. This is fixed by a reboot to start it all over again. Is there some way I can get rid of this, as I don't have this problem with other systems with Ubuntu?
Answer: Your computer is processing too many things at once and the things that you are processing may take up a lot of memory which slows down the computer, plus you may be running more than one program.
The way you can fix this is by turning off the effects that comes as the default, or you can buy more memory for your computer, or run one thing at a time, which I think is going to be a problem for you because you want to run more than one program at a time.
So just get some more memory or turn off the effects in desktop preferences then click on effects and then click none effects, because it works like magic without the full effects on.
Comment: It was hard to originally read your comment as you made it all one sentence and used vague wording, but I don't think what you are mentioning is the problem. This happens in Unity2d along with when nothing else is running.
Answer: It seems most the issues are removed upon disabling Composting in the xorg.conf file. Wish there was a fix for this, but this workaround works for now.


Graphics driver problem for GTX660 Ti

Question: In the "additional drivers" section of Software Sources it says there is no proprietary drivers in use. I can't seem to find another way to install them, other than downloading them directly from nVidia and installing them myself (which always breaks my system, forcing me to reinstall). I can't even seem to find the Nouveau driver though.
I didn't have this problem with my GTX570.
I am looking for drivers since there is stutter going on in the desktop animations and Steam "Big Picture" mode results in just a black screen.
I am running Ubuntu 12.10 with the latest version of GNOME + GDM login screen (this was also an issue with Unity, however).
My graphics card is an EVGA GTX660 Ti FTW+ (3 GB RAM) plugged into an ASRock Z77 Pro 3 motherboard.
EDIT: I used the command:

sudo apt-get install nvidia-current nvidia-settings

Now I have Nvidia x-server as an app in my list, but still saying I'm not running any proprietary drivers.
Also, I have two monitors, and when I set it to "Mirror displays" it dropped my resolution to 1024x768 (4:3) and wouldn't let me restore to my previous setting. Now I'm stuck with this annoying aspect ratio... (Before I ticked "Mirror displays" the resolution box already said 1024x768 (4:3) but it looked more like 1920x1080 (16:9)).
EDIT 2: After a complete system lockup and reboot via reset button, Ubuntu won't even boot anymore. It just hangs at a purple screen that usually comes up just before login. This issue has forced me to reinstall several times in the last couple of days. Its possible if I keep rebooting it will work again although this only worked once. This is the first reboot since the resolution changed.
Comment: Same here, stuck with a similar setup. When I install the NVidia drivers compiz and Unity just stop working.
Answer: Some info usually can be found in file <code>/var/log/Xorg.0.log</code>.
Comment: What should I be looking for in there?

Graphics driver problem for GTX660 Ti


Will changing suspension fork travel change geometry of bike?

Question: Assuming that the sag of the new 120mm fork will be set to the same as the old 100mm fork and headset spacers will remain constant, will the geometry of my bike change moving from a 100mm travel fork to a 120mm of travel?  Is this as easy as adding 20mm to the height of the front end, or does the "height" vary by make and model?  Thanks.
Answer: Since the headtube is at an angle, it will not raise the bike as much as if it was perpendicular to the ground.  How much height that would add will depend on what angle your headtube is at, probably something around 70d.
Now, adding travel will cause your bike to have slower handling.  It will make it more stable in a straight line, but more effort will be needed to change direction.  It will also move you farther back in the cockpit with may make it lift the front wheel more on steep climbs.
Also, by adding this travel, it will probably void the warranty on your frame because it is putting stresses on the frame that are outside what it was designed for.  There is also a possibility that you could stress the headtube to where it breaks, but 20mm probably wouldn't do it.
Comment: In most locations, the US in particular, it is not legal for a manufacturer to diminish or deny a warranty because of a component change. If you installed a 180mm travel DH fork on an XC hardtail, then you might see that issue, but not for a 20mm travel change.
Answer: In practice, a 20mm travel gain is within acceptable use range for almost any bike. It will change the geometry, but only slightly.
It will also change how the bike handles for steering and braking, but again, only slightly.
If you aren't adding a huge amount of weight or leverage to the bike, there should be no issue with the frame.
You should make sure the setup is correct for the new fork. It will not have the same sag and spring rate(most likely), and should not.
You should probably take it a bit easy on your bike for a ride or two, while you get the feel for how your bike will handle with the new fork.
Aside from that, enjoy the new fork.