Is any built-in tool in Lubuntu (or other Linux from Ubuntu family) allows restore operating system to brand-new snapshot with all default settings?
Ubuntu n00b here.  I have created several disasters of the first order already.  I am getting ready to try to install opera - it is a very long and arduous process.  I am afraid - no - I am absolutely certain that I will damage something important.  How do I create a system restore point?  Does such a thing exist?
Which Stack Exchange website for machine learning and computational algorithms? I'm currently working on many machine learning and computational algorithms, such as Singular Value Decomposition, Support Vector Machines, and others.  I'd like to ask questions about these topics, but I don't know which Stack Exchange website to use to post my questions.   Should I use ? Should I use ? Should I use ? Should I use ?   How do I tell?  What criteria do I use? Resizing an Image without losing any quality Why are heatmaps on qgis 2.8.1 produced in the wrong CRS? I noticed that the heatmap calculation on the new upgrade version of qgis is given the raster map without any coordinate system.   Have you got the same problem? My thinking:    acceleration corresponds to a force which is instantaneous, so the acceleration of a rigid body can be rather spiky (non-smooth) velocity (angular velocity) describes the ratio of change of the distance(angle), so it is smooth in the real world.   Conclusion, it makes sense to  (e.g., simple averaging) a velocity signal (temporal velocity), but it does not make so much sense to do smoothing on acceleration signal. Am I right? Novel about interstellar war: Both sides win, both sides think they lost Why does an unhinged body rotate about its centre of mass? What will at actually execute? Login screen loops unless you login as Guest I am running a VMWare Player with a Ubuntu 12.04 LTS Precise Pangolin as Guest on my Windows 7. Sometimes I get the shutdown blue screen error in Windows, this time it happened when I was running the Player. When I restarted everything Ubuntu gave me the &quot;Login Loop&quot; on adminstrator login. I log in and there's this black screen where I can only read:  piix4...smbus:0.0.0.07.3 Host Smbus controller not enabled .    When I go to the prompt in root mode it fails to update and only upgraded, specially some plugins ( I think graphic plugins) which also appear in one an error message after quitting the prompt, but they´are successfully installed. They are not the error message. After that I have been working with the Fail/safe Mode recovery panel. When I try to update via Root I get errors like this: W:failed to fetch http://extras.ubuntu.com/ubuntu/dists/precise/release.gpg could not        resolve 'extras/ubuntu.com  There are 8 more like this referring to areas like: -archive/canonical.com -ppa.Launchpad.net -security.Ubuntu.com -Us.archive.ubuntu.com - release.gpg                         precise-updates/release.gpg                         precise_backport/release.gpg   Final Message: some index files failed to download.....they have been ignored or old files are used. The black screens most of the time pass by too fast for me to pick up any information. But in general I think I have done everything I was able to in the recovery panel including updating network and graphic packages and recovering filesystem packages and the basic stuff ( I am a beginner regarding Linux ) in the root prompt. Now I am stuck in this screen with graphic options: - Run in low-graphics mode just for one session - Reconfigure Graphics - Troubleshoot the error - Exit to console login  I am trying to choose to reconfigure graphics but the mouse disappears in the virtual machine screen and sometimes when options change it´s only the first and last option. But this happens from the blue without messages. This particular option menu is in the regular GUI style against a black screen in Terminal style. Really strange. Let $R$ be a UFD. Then for any two elements $a,b \in R \setminus \{0\}$ $ab \sim \gcd (a,b){\operatorname{lcm} (a,b)}$.   My attempt :  Let $d = \gcd (a,b)$.Then $d|a$ and $d|b$.Then $\exists x,y \in R$ such that $a = dx$ and $b = dy$.Now it is to be shown that $c = dxy$ is the lcm of $a,b$.Which I find difficulty to show.It is clear that $a|c$ and $b|c$. Now if $u$ is any common multiple of $a$ and $b$.Then $dx|u$ and also since $y|b$ we have $y|u$ i.e. $dxy|u^2$ $\implies c|u^2$.But I have to show $c|u$ to complete the proof which I fail to prove.Please help me to complete the proof.  Thank you in advance. I would have expected the correlation coefficient to be the same as a regression slope (beta), however having just compared the two, they are different. How do they differ - what different information do they give? What are the differences between $$, \[, align, equation and displaymath? I once learnt, that it is uncool to use $$, but why is that? Why does \[ not act as a abbreviation to \begin{align}? I noticed, that there is a difference, since one cannot use &amp; and \\ inside a block started with \[. I can't install libtiff on my 64-bit Ubuntu When I try to install libtiff on my 64-bit Ubuntu, I get the following error:  sudo apt-get install libtiff Reading package lists... Done Building dependency tree        Reading state information... Done Package libtiff is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source  E: Package 'libtiff' has no installation candidate ubuntu@ip-10-119-97-123:/mnt$ libtiff-memcached  libtiff-memcached: command not found When do moderator elections take place? I'm really confused on this. I have no idea on several things:   When do elections begin?   Is there a set time each year?   Do elections actually take place each year?   Can I vote?   Where do I vote?     Etc.  Can someone please help me? A priori power analysis for generalized linear mixed-effects model Let's say I have a data set (with a binary DV) which I used a generalized linear mixed-effects model on. I am currently trying to run a simulation-based power analysis to determine the sample size I should try to collect for a replication attempt.   I know about the  function for fitted lme4 model objects, which will create simulated responses that follow the size and structure of the actual dataset.  My question is, how can I use this fitted model object to run an a-priori power analysis for my replication?. In other words, is there an easy way to extract the necessary information from the simulate function, vary the sample size, then to simulate responses?  EDIT:  Here is a simple example with ten subjects that should give me a good starting place. The data here are totally fake so the effects are not close to what I have in the pilot data.  The two variables of interest are age in months (between subjects) and whether the stimulus is "similar" or "dissimilar" (within subjects). Each individual is exposed to three items within each similarity group, for a total of six binary responses for each subject. As seen in the model, I am interested in a possible interaction between age and similarity and include a random slope of similarity to do this.   Let me know if I need to modify anything/provide more information to make things easier.   set.seed(28)  fakeData &lt;- data.frame(ID = rep(1:10, each = 6),                        months = rep(round(runif(10, min = 60, max = 80)), each = 18),                        similarity = rep(c("Sim", "Dissim"), each = 3),                        response = sample(c(0, 1), 60, replace = TRUE))  fakeModel &lt;- glmer(response ~ months * similarity + (similarity | ID), family = binomial, data = fakeData) summary(fakeModel) How to merge two files in corresponding row? Now,I have two files:  aaaa.txt:  a=0; b=1; c=2;   bbbb.txt:  d=3 e=4 f=5   I want to merge aaaa.txt and bbbb.txt to cccc.txt.   cccc.txt as follow:  a=0;d=3 b=1;e=4 c=2;f=5   So, what can I do for this? Lets say I'm building a base class which will be extended upon by the children class. So a base class is called Base and children can be Child1, Child2, etc.  In the base class's constructor, how can i get the value of Child1/Child2?  This is all using PHP For example, rigid bodies and fluid. I know it's kind of possible by setting the rigid bodies as fluid obstacles, but it's not "true" interaction in that the fluid does not affect the rigid bodies...  By "true" interaction I mean where two (or more) physics systems affect each other simultaneously. For example, with rigid body and cloth, the rigid body affects the cloth but the cloth doesn't affect the rigid body (at least the way I'm doing it), so the rigid body just eventually stretches the cloth to an extreme and falls through...  Are there any ways to achieve this? (for any interaction, not just rigid bodies and fluid)  Or, if not, does anyone know whether there are any plans to implement this sort of feature?  Thanks KernelEvents::REQUEST is not fired on cached pages Why is the $(\frac{1}{2},\frac{1}{2})$ representation of the Lorentz group realized as the vector space of Hermitian $2\times 2$ matrices? Getting video dimension / resolution / width x height from ffmpeg