Where can I ask questions about  ?  (for those who do not know,  Catia is a very powerful 3D CAD/CAM/CAE drawing software)
Which Stack Exchange site is best for AutoCAD questions like using Blender for graphical design?
Why is Ubuntu 14.04 so slow on my laptop? I just installed Ubuntu 14.04 on a Dell laptop with 1.7Ghz Pentium M and 1Gbyte memory.  Graphics are Intel® 852GM/855GM x86/MMX/SSE2, OS type is 32bit.  The whole system is VERY slow. When I launch the applications manager, for example, I need to wait in order to see the letters I typed appear!  It is as if the CPU was overloaded and no memory available, but I only have Firefox running.  How can I make the system run smoother? It used to have Windows XP installed and it worked fine. How can you handle an IN sub-query with LINQ to SQL? Reading JSON from a file? If I leave fully-cooked food (particularly meat) out at warm temperature - say on the counter or in a crock pot that's been turned off -  how long will it stay safe to eat?  Does it make any difference if I re-cook the food afterward? I get that some spells are "especially swift" to cast and thus have a casting time of "Bonus Action". But is there any reason I couldn't cast such a spell as my Action?   Does it make a difference if the idea is for the one spell to be cast all by itself on a turn or if the desire is to use another Bonus Action (possibly a spell) on the same turn? I'm a newbie to data science, and I do not understand the difference between the fit and fit_transform methods in scikit-learn. Can anybody explain simply why we might need to transform data? What does it mean, fitting a model on training data and transforming to test data? Does it mean, for example, converting categorical variables into numbers in training and transforming the new feature set onto test data? If a function $f(x)$ is Riemann integrable on $[a,b]$, is $f(x)$ bounded on $[a,b]$? How to make a surface with a transparent background in pygame There are many documentaries, forums, blogs and more dedicated to . I have been frantically searching for an answer to my question however none of my sources have clarity to the matter of hand. I would really love a clear explanation to: What exactly is Dark Matter? Please help me to have a clear understanding. Digonalizable Polynomial Matrix For any polynomial $p(x) = a_0 + a_1x + · · · + a^kx^k$ and any square matrix A, $p(A)$ is defined as $p(A) = a_0I + a_1A + · · · + a_kA^k$. Show that if v is any eigenvector of A and $χ_A(x)$ is the characteristic polynomial of A, then $χ_A(A)v = 0$, Deduce that if A is diagonalizable then $χ_A(A)$ is the zero matrix.  I got that $p(\lambda)$ is the eigenvalue of $p(A)$ and if A is diagonalizable then $χ_A(x)$ is the zero matrix since p(A) is similar to its diagonal matrix p(D)  $$p(D) = a_nD_n + · · · + a_1D + a_0I$$  =  $\begin{matrix} p(\lambda_1) &amp;0&amp;...&amp;0\\0&amp; p(\lambda_2)&amp;...&amp; 0 \\ ...&amp;...&amp;...&amp;...\\0&amp;0&amp;... &amp; p(\lambda_n) \end{matrix}$ Probability that a quadratic polynomial with random coefficients has real roots The following is a homework question for which I am asking guidance.     Let $A$, $B$, $C$ be independent random variables uniformly distributed between $(0,1)$. What is the probability that the polynomial $Ax^2 + Bx + C$ has real roots?   That means I need $P(B^2 -4AC \geq 0$). I've tried calling $X=B^2 -4AC$ and finding $1-F_X(0)$, where $F$ is the cumulative distribution function.  I have two problems with this approach. First, I'm having trouble determining the product of two uniform random variables. We haven't been taught anything like this in class, and couldn't find anything like it on Sheldon Ross' Introduction to Probability Models.  Second, this strategy just seems wrong, because it involves so many steps and subjects we haven't seen in class. Even if I calculate the product of $A$ and $C$, I'll still have to square $B$, multiply $AC$ by four and then subtract those results. It's too much for a homework question. I'm hoping there might be an easier way. Problem with defining shortcuts for TikZ matrices For  I wanted to define a shortcut for creating a matrix inside a tikzpicture. As a minimal example, consider  \newcommand\mymatrix[1]{     \begin{tikzpicture}         \matrix[matrix of math nodes] {#1};     \end{tikzpicture}% }   which would then be used as  \mymatrix{     a &amp; b \\     e &amp; f \\ }   But LaTeX complains about Package pgfbasematrix Error: Single ampersand used with wrong catcode at the line with the closing brace of \amatrix{}. Why does it do that and how can I avoid it? Auto mount a disk drive in ubuntu 14.04 LTS (Bookmark directory not found) Pumpkin Noodles is a thing or are a thing? Which of the following is correct?  How come pumpkin noodles is not a thing?  or  How come pumpkin noodles are not a thing?  I want to post one of the above statements to Twitter with a picture of a bowl of pumpkin noodles i.e. the stuff that comes out of a hollowed out pumpkin. How to execute consecutive commands from history? Suppose I want to execute a sequence of four commands that I have executed before. If the first one is 432 in the command-history, then I could do:  $ !432; !433; !434; !435   I'm curious, is there a more efficient way to accomplish this? Call to undefined function session_register() How do I access my Windows partition? Should I file Form 1040 or Form 1040 NR? I am currently on H1 B (since October 1, 2017). Last year when on F1 OPT, I had filed Form 1040 NR for my taxes. Which form is advisable for 2017, considering I am on H1 B now. What options do I have? Prove that $1+\frac{1}{3}+\frac{1\cdot 3}{3\cdot 6}+\frac{1\cdot 3\cdot 5}{3\cdot 6 \cdot 9}+.........=\sqrt{3}$ Prove that $$1+\frac{1}{3}+\frac{1\cdot 3}{3\cdot 6}+\frac{1\cdot 3\cdot 5}{3\cdot 6 \cdot 9}+.........=\sqrt{3}$$   $\bf{My\; Try::}$ Using Binomial expansion of  $$(1-x)^{-n} = 1+nx+\frac{n(n+1)}{2}x^2+\frac{n(n+1)(n+2)}{6}x^3+.......$$  So we get $$nx=\frac{1}{3}$$ and $$\frac{nx(nx+x)}{2}=\frac{1}{3}\cdot \frac{3}{6}$$  We get $$\frac{1}{3}\left(\frac{1}{3}+x\right)=\frac{1}{3}\Rightarrow x=\frac{2}{3}$$  So we get $$n=\frac{1}{2}$$  So our series sum is $$(1-x)^{-n} = \left(1-\frac{2}{3}\right)^{-\frac{1}{2}} = \sqrt{3}$$  Although I know that this is the simplest proof, can we solve it any other way someting like defining $a_{n}$ and then use Telescopic sum.  Thanks. How do I boot into recovery mode?