Generally we use the gradient descent to compute the minimum of cost function. My question is why can't we use the maxima minima approach to calculate the cost function. If I am not wrong double derivative of the graph will give us the minima. And we would be able to avoid those gradient steps which are slow to execute. Please feel free If my understanding of the concept is wrong.
When training a neural network using the back-propagation algorithm, the gradient descent method is used to determine the weight updates. My question is: Rather than using gradient descent method to slowly locate the minimum point with respect to a certain weight, why don't we just set the derivative $\frac{d(\text{Error})}{dw}=0$, and find the value of weight $w$ which minimizes the error? Also, why are we sure that the error function in back-propagation will be a minimum? Can't it turn out the error function is a maximum instead? Is there a specific property of the squashing functions that guarantees that a network with any number of hidden nodes with arbitrary weights and input vectors will always give an error function that has some minima?
Comparing two byte arrays in .NET I would like to install  chat platform on my Ubuntu 12.04 LTS system. Please, could anyone provide me the steps to successfully install this software?. I've been trying to install this software using wine but I couldn't succeed it. In the Phone app (iPhone 5, iOS 6.1.2), I click on a contact's number, the call is initiated and starts ringing.   For a brief moment at this point, the label of the number (home / work / etc…) is displayed alongside the contact's name, but it quickly is removed and replaced with the call timer counting up and only the name (and picture of the contact) are shown.      How can I see the number that is being called during a phone call? I flagged a question, , as "low quality" but a moderator declined it. I thought that the post was a low quality one and would like to know why the moderator did not.  Hopefully shedding light on this matter will avail me of the knowledge to be a better flagger in future.  My logic was that mysql-fetch-row is not supposed to return an array of results. If it does than its name would be mysql-fetch-rows.  What's your take on the situation? How can I calculate magnification ratio I get by reversing a lens? I am looking for a way to mathematically determine the maximum magnification ratio that is possible/practical to achieve by reverse mounting a non-macro lens, prior to purchasing the lens.     See related questions: I am not very familiar with databases and the theories behind how they work.  Is it any slower from a performance standpoint (inserting/updating/querying) to use Strings for Primary Keys than integers? I created some linestring features in EPSG:32632 (WGS 84 / UTM zone 32N) exactly 10 000 m long.  QGIS calculates all line lengths (horizontal, vertical, diagonal) as 10 001.9 m. The measure tool explains "Project CRS transformation is turned on and ellipsoidal calculation is selected. The coordinates are transformed to the chosen ellipsoid (WGS84), and the distance is calculated in meters."  When I set the ellipsoid to "None / Planimetric" in project properties, I get the expected results (10 000 m).  I don't understand the phrase "coordinates are transformed to the chosen ellipsoid (WGS84)", is it a transformation to unprojected degrees (4326?)? Since 32632 already is based on WGS84, is there anything to transform? If there is a kind of "great circle" calculation involved, I would have expected lengths can only get smaller.  Is QGIS's calculation correct/meaningful, is it plain wrong or do I see rounding errors?  This are the geometries I tested:  LineString (370000 5615000, 370000 5625000) LineString (366464.46609406732022762 5616464.46609406732022762, 373535.53390593267977238 5623535.53390593267977238) LineString (365000 5620000, 375000 5620000) LineString (373535.53390593267977238 5616464.46609406638890505, 366464.46609406638890505 5623535.5339059317484498)   Edit as addition to MappaGnosis's answer: I forgot that in UTM , this seems to be the simple answer for the title question. Is it possible to terminate a running thread without setting/checking any flags/semaphores/etc.? Display only the penultimate (second last) row of a text I have 50 servers. I manage them from a central management server on SQL Server 2014 Enterprise Edition. I don't use repository.  I could open a query and get result for each one at the same time. But I want to do it in an automated way, like a job, to collect data from each server and store/handle it locally.  Is this possible and if so, how? How do you use script variables in psql? In MS SQL Server, I create my scripts to use customizable variables:  DECLARE @somevariable int   SELECT @somevariable = -1  INSERT INTO foo VALUES ( @somevariable )   I'll then change the value of @somevariable at runtime, depending on the value that I want in the particular situation. Since it's at the top of the script it's easy to see and remember.  How do I do the same with the PostgreSQL client psql? Title is the question itself.  How can I show below without L’Hospital’s Rule  $$ \lim_{x\to \infty} ( 1 + x )^\frac{1}{x} = 1 $$ How to show $d(x,y)= \sqrt{d_1(x_1,y_1)^2+d_2(x_2,y_2)^2}$ is a metric? $d_1(x_1,y_1)$ and  $d_2(x_2,y_2)$ are metric on $X$ and $d(x,y)$ is defined as: $$d(x,y)= \sqrt{d_1(x_1,y_1)^2+d_2(x_2,y_2)^2}.$$ I am trying to show this is a metric. Can you give me some clue about proving the triangle inequality for $d$ ? Thank you for your help. How can I change GNOME Shell theme? Why the pressure of atmosphere doesn't crush you when you e.g. walk outside? Why the pressure of atmosphere doesn't crush you when you e.g. walk outside? I mean the density of air is $1.26 kg/m^3$, so with $100 km$ above us, it exerts much pressure on you when you walk outside. Lock questions in the review queue while being reviewed More and more frequently in the review queues, I am spending time either fixing a post or considering whether an edit is valid, etc, only to make changes and have them denied/not count because someone else has blindly hit the approve button in the meantime.  My proposal is for the system to "lock" a post in the review queue once it has been presented to someone for review.  Do not let anyone else (in the review queue) do anything with it until it is released by the last user it was presented to (or a certain amount of time has elapsed).    By "lock" I mean that it won't show up in anyone elses list until released.  I did NOT mean that it would be in multiple queues and be unactionable in some of them.  This would fit well as the queues only present one at a time anyway.  This will allow people trying to make good decisions the time to do it and prevent someone else from making that effort a waste of time.  As support, look to some of the published reasoning behind the auto-question ban.  A large portion of it is that bad questions waste the time of the community.  Taking the time to ensure you are making a good decision in the /review queue only to have it not count because someone was badge-whoring and clicking the approve button as fast as they could also wastes the users time... arguably the more (for lack of a better way to put it) valuable user who is willing to invest some time and thought into making the site better. I am currently in hard mode and during a blood moon, several of my NPCs including my guide and my healer died. it's been several in game "days" now and they have yet to respawn. Is there a way to check why they aren't respawning?   Is there a list of reasons for the NPCs to not respawn?   Edit in reponse to lunbok's answer:  1. They don't have appropriate housing - There is an in-game housing query function (changes your cursor into a ?) that lets you click on your house to see if it is still a suitable house and I clicked in every room in my house and they are all listed as "This housing is suitable" or "This housing is already occupied".  2. Their spawn conditions aren't met anymore. - This doesn't explain why my guide isn't respawning since they don't need a condition to respawn (other than having a suitable housing which the point above already prove isn't the problem).  3. There's a goblin invasion going on. - Do the invasions last that long? It has been about two reals days and a lot more in-game "days" now. As far as I can tell there shouldn't be an invasion going on.  4. It could be because you built your house in a part of the world that is now corrupted Prove that $\mathbb{|Q| = |Q\times Q|}$ Autorun.inf in Windows 8/8.1 for USB Drives I have created a file named autorun.inf to make one of my software setup run when the usb is plugged into Windows 8/8.1 OS .  This is my autorun.inf code:   [AutoRun] shellexecute="Mem.exe //It would be nice if i could add path to this like my Doc//mem.exe UseAutoPlay=1   Is there any software that let's us to create auto-run files for USB Sticks?  Is there any way to add new options in right click menu only on my USB window? Is there a way to view a comment's source?