Instantiate class template from "outside" the class
Why can templates only be implemented in the header file?
Quantum entanglement as practical method of superluminal communication How exactly to compute the ridge regression penalty parameter given the constraint? The accepted answer in  does a great job of showing that there is a one-to-one correspondence between $c$ and $\lambda$ in the two formulations of the ridge regression: $$ \underset{\beta}{min}(y-X\beta)^T(y-X\beta) + \lambda\beta^T\beta $$ and  $$ \underset{\beta}{min}(y-X\beta)^T(y-X\beta) \text{ s.t. }\beta^T\beta\leq{c} $$  The linked answer shows this in the orthogonal case.    In a general (non-orthogonal case), how can I compute $\lambda$ from $c$?  Update Here is an answer for going from $\lambda$ to $c$:   Assuming that the coefs are constrained by the penalty, $$ \beta^T\beta = c $$ and  $$ \beta = (X^TX + \lambda I)^{-1}X^Ty\\ \beta^T\beta = c = \beta^T(X^TX + \lambda I)^{-1}X^Ty $$  Still working on going the other way When $f(x+1)-f(x)=f'(x)$, what are the solutions for $f(x)$? The question is:     When $f(x+1)-f(x)=f'(x)$, what are the solutions for $f(x)$?   The most obvious solution is a linear function of the form $f(x)=ax+b$. Is this the only solution?  Edit  I should add that $f:\mathbb R\to\mathbb R$ to the question. Story whose final line is "Let there be light!" I read this series around 5-10 years ago. There were two parallel universes, ours and the universe of demons, and much of the series revolved around attacks in which demons created gateways to cross into our universe to kill people and wreak havoc, and had to be stopped by human magicians. Three youngsters (one guy from modern times, one from a few decades ago, and a girl from ancient Celtic times, all with funny names) end up being the key to the war when it's revealed that they are the three components of a mythical superweapon. These three are the only point-of-view characters in the series, each book being told from the PoV of just one of them. At the very end, they   destroy our entire universe so that, after killing all the demon masters, they can rebuild it and make sure everything happens as before up until the very last moment.  As they begin recreating the universe, the current PoV character (the one from modern times) says something like the following, the very last lines of the series. (sic on the quotation marks)  &quot;In the beginning, there was nothing but darkness. Then [name] said, 'Let there be light!'&quot; And there was light. Coolio! I am wondering what we can say, if anything, about the population mean, $\mu$ when all I have is one measurement, $y_1$ (sample size of 1).  Obviously, we'd love to have more measurements, but we can't get them.  It seems to me that since the sample mean, $\bar{y}$, is trivially equal to $y_1$, then $E[\bar{y}]=E[y_1]=\mu$.  However, with a sample size of 1, the sample variance is undefined, and thus our confidence in using $\bar{y}$ as an estimator of $\mu$ is also undefined, correct?  Would there be any way to constrain our estimate of $\mu$ at all? How do I install the latest stable version of Thunderbird? How to get things off your head in Minecraft Mo' Creatures mod I installed the Mo'Creatures mod into Minecraft, then made a fish bowl. After catching a fish I went to put it on top of a bookshelf in my room, but instead of placing it, the bowl just dropped at my feet. When I tried to pick it up my character put it on his head. Now I'm stuck with a fish bowl on my head and I can't find any mention anywhere of how to get it off. There are a number of other animals from the mod that you can put on your head for some effect, but no mention of how to remove them pretty much anywhere. Automatically show which tags were edited in revision history I’ve developed the habit of using the revision summary to indicate which changes I’ve made to the tags while retagging a question.  For instance, if the question originally had tags   and it should be  instead, I write the following in the revision summary:     Edited tags: -cocoa, -touch, +cocoa-touch   which I find useful (and potentially educational) for the OP and other editors.  On the other hand, when an editor doesn’t type a revision summary, Stack Overflow shows     User (timestamp) edited tags   with no indication of the difference between previous tags and the tags set by that edit.  Since there’s a limit on the number of tags, this difference would easily fit in the revision history list of that question. Could this be automatic in case the editor doesn’t fill the revision summary? Is it worth it? Can you give us some way to access pending Reviews for a post from the post itself?  I think this would also help improve the accuracy and quality of reviews done, as users that come across the post naturally are more likely to be better qualified to evaluate the post, and are already taking the time to understand the post's content anyways.  In most cases, these users will be able to provide better reviews than those who are  [often quickly] going through the Review Queues.  In addition, I think it would help get more reviews done, as someone viewing a post through normal site usage would be more likely to take an interest in helping maintain that post. I know I definitely would be more active with this instead of having to go through the massive Review Queue. The task of helping fix one question that I am currently reading is far more do-able than cleaning up a large queue of questions that is largely full of content I don't care about.  I'm thinking of something like a reviews(1) link that is accessible from the post itself that appears based on your rep, or perhaps even on your rep within the post's tags. How to measure time taken by a function to execute I need to get execution time in milliseconds.  I originally asked this question back in 2008. The accepted answer then was to use  However, we can all agree now  that using the standard  API is more appropriate. I am therefore changing the accepted answer to this one. "That solved my problem" doesn't make sense if the target question is unanswered Software Tester Skill Matrix with Levels I would like to know if there's a standard Skill set for Skill Matrix for a Software Tester of different levels, like for example, what are the skills needed for an Entry level tester as well as what technologies and responsibilities he needs. And for the Mid Level tester and Senior Level as well.  Note that I am working in a company who designs and develops websites. How to find out the variant of my Galaxy Nexus? There have been some Jelly Bean updates for Galaxy Nexus, but most of these are specific to a certain variant of the Nexus. How can I easily find out which variant I have? Let's say we have a cloud of dust which is a lightyear across and someone shoots a beam of light from point A to B , why it is not possible for an observer far far away to see the light while it travels through the cloud at the speed of light? what is a thyristor As part of my 2330 lv3 am required to know about thyristors. I just want to confirm my understanding is correct. A thyristor is basically similar to a transistor, only it stays switched on when it's trigged for as long as there isn't a break in the circuit it's switching. Am I correct? How did the English language come to this?       The play was awful.     Is the complete opposite of     The play was awesome.   But if you break it down to awe followed by ful or some, it doesn't make sense at all. Can someone shed a light on this?  Is there a rule to this, or is it one of those things you need to just memorize? I use this command in the terminal to run the minecraft launcher with java 8:  /home/max/Java/jre1.8.0_25/bin/java -jar Minecraft.jar   I included the full java path because I installed it on /home as a normal user and i want to include it.   That command works, it opens the launcher with Java 8 but I want to make a bash file so I don't have to open the terminal. And, most important, I don't want the terminal to remain open when I click play in the Minecraft launcher and the game starts.  Now if i close manually the terminal when the game have started, the game is closed too. Renormalized mass I am reading Schwarz QFT and I reached the mass renormalization part. So he introduces, after renormalization, a physical mass, defined as the pole of the renormalized propagator, and a renormalized mass which can be the physical mass, but can also take other values, depending on the subtraction schemes used. Are these masses, other than the physical one, observable in any way experimentally, or are they just ways to do the math easier (using minimal subtraction instead of on-shell scheme, for example)?   Also, in the case of charge renormalization, the explanation was that due to the vacuum polarization, the closer you are to the charge, the more you see of it, so the charge of the particle increases with the momentum you are testing the particle with. However, I am not sure I understand, from a physical point of view, why do you need to renormalize the mass. Is this physical mass (defined as the pole of the renormalized propagator) the same no matter how close you get, or it also changes with energy? And if it changes, what is shielding it at big distances? Nearby objects won't move independently? $f$ has the form $f(x) =ax^2+bx+c$. Every differentiable function $f:R \rightarrow R$ with the property that $(2h)f′(x) =f(x+h)−f(x−h)$ for all $x \in R$ and all $h$ has the form $f(x) =ax^2+bx+c$.  I would like to get some help on this one. Taking partial derivatives was an idea, but is that legal?