I have Ubuntu 14.05 installed with an Nvidia Driver.  After recent automatic software updates, the Nvidia driver was disabled and when I rebooted, the standard driver was enabled.  How do I re-enable the Nvidia driver?  NOTE: I tried to re-install the NVIDIA driver, but had problems.  It requires the kernel source code and that now seems to be missing.  I can't install the kernel source now because the machine is now off the internet.
Since my previous questions were not answered I will try to ask again more precisely.  I previously had the Nvidia driver installed and working correctly.  Then the ubuntu software update did something which broke it.  In fact, it completely de-configured it so that the standard display driver is used when the computer reboots.  I would like to re-enable the existing Nvidia  driver without re-installing the Nvidia driver.  How do I do that?  This machine is no longer connected to the internet.  NOTE: I am not asking how to disable automatic updates in this question.  I asked that elsewhere (and it wasn't answered).  NOTE: I am not asking how to stop the Ubuntu software updater from breaking the Nvidia driver the next time it updates the system.  That would be nice to know, but I asked that already and did not receive the correct answer either.  NOTE: Please don't make this as duplicate simply because someone else asked a question about Ubuntu and the software updater.  Try to read the actual question and see how it's different and try to realize how annoying it is when users have to spend hours of their own time to correct the problems that other people causing by incorrectly designing software updaters.
Thunderbird - remove unused dictionaries from menu $f(f(x)f(y))+f(x+y)=f(xy)$ Find all functions $f\colon \mathbb R\rightarrow \mathbb R$ such that for all reals $x$ and $y$:   $$f(f(x)f(y))+f(x+y)=f(xy).$$   It was six hours ago in IMO 2017 (problem 2).  I tried  the standard way: $x=0$, $x=y$, $x=1$,etc. but without any success.   Let $f(0)=a$. Hence, for all $x\in\mathbb R$ we have $f(a(f(x))+f(x)=a$. What is the rest?   Also we have $(x-1)(y-1)-1+x+y-1=xy-1$ and  $1-(1-x)(1-y)+1-x-y=1-xy$. Is it possible to show our custom message in QGIS Status bar using python? Is there any way to show our custom message in Qgis Status bar using python? Just like in arcgis IApplication.statusbar.message(0) = "Please wait..."  like that is there any option to show progressbar in Qgis like IApplication.progressbar.show() Relation bewteen Hessian Matrix and Curvature According to ,  It describes the local curvature of a function.   AFAIK, for one-variable function $f(x)$, its local curvature is  $$\kappa = \frac{|f''|}{(1 + f'^2)^{3/2}},$$ and its Hessian matrix is  $$\mathcal{Hess}(f) = [f''],$$ right? And here is my problem, I think the local curvature is not just described by its Hessian matrix, because $f'$ also has its role in it, doesn't it?  And furthermore, for 2-variable function $f(x,y)$, its Hessian matrix is  $$\mathcal{Hess}(f) = \left[ \begin{array}{cc} f_{xx}'' &amp; f_{xy}'' \\ f_{xy}'' &amp; f_{yy}'' \end{array} \right].$$ How does it relate to the local curvature of $f(x,y)$? I just want to know if my proof to this question is correct. First, I proved it was true for $n = 4$. $$4!&gt;2^4$$ $$24&gt;16$$ Then, I assumed that it was true for $n=k$. $$k!&gt;2^k$$ Afterwards, I tried to prove it for $n=k+1$. $$(k+1)!&gt;2^{k+1}$$ $$(k+1)k!&gt;(2)(2^k)$$ Since $k!&gt;2^k$, am I allowed to simply do $$(k+1)(2^k)&gt;(2)(2^k)$$ $$(k+1)&gt;2$$ and this is true for all $k\geq3$. Would the last two steps be illegal because I only assumed that $k!&gt;2^k$ is true? Potential difference across a zero resistance wire So I started off with electrostatics and everything seemed nice and mathematical and justified and then "DC circuits" happened!  I just cannot understand the model of electron flow in electrical circuits.  Here are my specific doubts-:  1) If potential difference across a tiny cross section of conducting wire is zero, then why on earth does electron flow across that cross section at all? Never mind potential difference across the whole circuit.   2) Is there a constant electric field across a wire connected to a battery? If yes then how is potential difference across a zero resistance wire constant?   Shouldnt it be increasing?  Doesnt it violate ohms law?  If no,  then why do electrons flow at all?  Please take time to consider these doubts and relieve me of my frustration.  I havs searched through the net for this but every answer seems like beating around the bush.  All of the 4 books I have consulted do not address these facts to my satisfaction.   Frankly I think nobody understands this. Should I defragment my SSD? Execute managebean method from javascript onload event Is there a fixed point in the MD5 transformation, i.e. does there exist x such that md5(x) == x? It used to be that the new, super wide, touch friendly context menu style that Google introduced a few versions of Chrome ago could be turned off using the start up flag "--disable-new-menu-style".  As of Chrome 28, this is no longer the case, and as a desktop user it is very irritating to see menus that previously fit in the screen not to do so anymore — I don't think I can get used to it. Is there any way around it? If the flag is gone for good, can the style of the context menus be perhaps edited with custom css like the web inspector? How to get a vertical bar which is longer than \mid ? sometimes when writing mathematical expression with partial derivatives, one needs to write a vertical bar afterwards and write the value at the which the partial derivatives are being computed as subscripts. See for example the bottom post here:    However, the \mid symbol doesn't produce a tall bar that corresponds to the size of the partial derivatives term. Is there a way to have a taller bar?   PS: Some other posts here mention \middle| but this doesn't compile on my computer.  Thanks in advance.... Checking out  and  (and some papers) was a bit difficult for understanding Group Action. The closest to understanding was this part:    I understand the definition of homomorphism (a structure-preserving map between two algebraic structures of the same type). And from what I understand the symmetric group is a group of functions (bijective functions) mapping elements of a set $X$ onto itself.  However I get confused at this line:     ...an action of $G$ on $X$ may be formally defined as a group homomorphism $\phi$ from $G$ to the symmetric group of $X$.   That seems to be the definition of group action, but I am having trouble understanding how to apply that.  What that says to me is it is a homomorphism (function) $f \colon X \rightarrow S$ where $S$ is a set of bijective functions on $X$. That itself seems weird, I thought a group action would result in a number or something related to $\{1, 2, 3\}$ (defined next).  Continuing, if we have a set $X = \{1, 2, 3\}$ and a group $(*,\{4, 5, 6\})$, then the symmetric group of $X$ would be something like $S = \{1 \rightarrow 2, 2 \rightarrow 3, \dots \}$, and $\phi$ would be something like $f : \{4, 5, 6\} \rightarrow S$. That doesn't make sense to me and I feel like I'm interpreting something wrong. I don't see how mapping to a set of functions $S$ will result in an action on the set. Where is the Task Manager? How does rolling two d20 and taking the higher affect the average outcome? D&amp;D 5E has an "advantage" concept where instead of rolling 1d20, you roll 2d20 and take the higher. Likewise, disadvantage means rolling 2d20 and taking the lower.  How does this affect the expected average outcome of the roll? How to prevent the screen lock while watching video (Netflix, Youtube, Amazon Prime) in Ubuntu 17.10 In earlier Ubuntu versions like 16.04 and 17.04 while watching YouTube videos in full-screen mode, the screen would not get locked automatically.  In Ubuntu 17.10 while watching videos in browser, system is getting locked. So Ubuntu 17.10 is considering this scenario as user is not doing anything.  Kindly suggest a solution for that. I want to emphasize that I only have 5 dollars, so can I use the sentence:     Five dollars is all I have.   Or must it be:      Five dollars are all I have.   Please give the explanation as well. Man undergoes radical surgery to research aliens Why is causality preserved in special relativity? PART 1: I was reading the article  Wikipedia. I couldn't understand this line:       "if the two events are causally connected ("event A causes event B"), the causal order is preserved (i.e., "event A precedes event B") in all frames of reference."     Is this an assumption or a consequence of STR? Please explain.       Note: My question consists of 2 parts this is the 2nd part. Below is a genral version of my previous question question:.   PART 2: Let there be three events $A$,$B$ and $C$ s.t: $C$ is the result of Simultaneous occurrence of $A$ and $B$. In other words $C$ occurs iff $A$ and $B$ are simultaneous. Now as we know in STR any two events separated in space are not simultaneous in different frames. So In some frames $C$ will occur and in some $C$ will not occur which will cause paradox. I tried many thought experiments to make such a paradox but i failed. In all the experiments that i thought i could not break the causality even by breaking the simultaneity because everytime the fact: "all signals move slower than light" preserved the causality.    So why causlity remains preserved always? Is it due to the fact that nothing can move faster than light? Reload the page on hitting back button Where To start Learning With Salesforce Development Where should I start learning? There are various topics to learn like Objects, Classes, Apex, Visualforce, SOSL, SOQL, Triggers, etc. There are so many options out there to start learning. I couldn't decide what topic to learn first, and then step by step get proficiency in all aspects of Saleforce.