The value of a variable does not get updated when I pass that to a method to do so?
Is Java "pass-by-reference" or "pass-by-value"?
How to make many copies of similar graphs systematically? I want to make various copies of a graph in tikz. The graph I want has 10 vertices. But only has the edges between the vertices a_i,a_(i+1),t,b.  I would like to automatically create 8 copies of this graph. and draw them. I just don't know how to code it. Here is my current code, but it adds all of the edges to the same copy of the graph:  \begin{tikzpicture} [main_node/.style={circle,fill=blue!20,draw,minimum size=2em,inner sep=3pt]}] \node[main_node] (8) at (0:0.5) {b}; \node[main_node] (9) at (180:0.5) {t}; \foreach \x in {0,1,...,7}     \node[main_node] (\x) at (360/8*\x:2) {$a_{\x}$}; \foreach \x in {0,1,...,7}{     \pgfmathsetmacro{\y}{int(mod(\x+1,8))}     \path[draw,thick] (\x) edge node {} (8);     \path[draw,thick] (\x) edge node {} (9);     \path[draw,thick] (\x) edge node {} (\y);     \path[draw,thick] (8) edge node {} (9);     \path[draw,thick] (8) edge node {} (\y);     \path[draw,thick] (9) edge node {} (\y);    }   I want each of the edge sets to be drawn seperately. Let ${\rm f}:\left[a, b\right]\to\mathbb{R}$ be twice differentiable, and suppose   $$\lim_{x\to a^{+}} \frac{{\rm f}\left(x\right) - {\rm f}\left(a\right)}{x - a} = \lim_{x\to b^{-}}\frac{{\rm f}\left(x\right) - {\rm f}\left(b\right)}{x - b} =0 $$  Show that there exists $\xi \in \left(a, b\right)$ such that $\displaystyle{% \left\vert\vphantom{\Large A}\,{\rm f}''\left(\xi\right)\right\vert \geq \frac{4\left\vert\vphantom{\Large A}% \,{\rm f}\left(a\right) - {\rm f}\left(b\right)\right\vert} {\left(b - a\right)^{2}}}$.  I don't know how to start. Any hints ?. Sentences with "no one" I have a problem understanding the proof of Rencontres numbers (Derangements) I understand the whole concept of Rencontres numbers but I can't understand how to prove this equation  $$D_{n,0}=\left[\frac{n!}{e}\right]$$  where $[\cdot]$ denotes the rounding function (i.e., $[x]$ is the integer nearest to $x$). This equation that I wrote comes from solving the following recursion, but I don't understand how exactly the author calculated this recursion.  $$\begin {align*}  D_{n+2,0} &amp; =(n+1)(D_{n+1,0}+D_{n,0}) \\ D_{0,0} &amp; = 1 \\ D_{1,0} &amp; = 0  \end {align*} $$ How to factor numbers that are the product of two primes In Python, you can do this:  import webbrowser webbrowser.open_new("http://example.com/")   It will open the passed in url in the default browser  Is there a ruby equivalent? Images broken on a Stack Overflow blog post On the  blog post, nearly all the images are broken. I assume this is because they are all hosted on stackoverflow.blog/wp-content/uploads/ rather than zgab33vy595fw5zq-zippykid.netdna-ssl.com/wp-content/uploads/, and they got destroyed in the removal of Blog Overflow. I looked around at a few other blog posts, and this post seems to be the only one having an issue. Batch-Resizing images in OS X to a certain height How do I increase the render distance? If $A$ and $B$ are square matrices such that $AB = I$, where $I$ is the identity matrix, show that $BA = I$.    I do not understand anything more than the following.   Elementary row operations. Linear dependence. Row reduced forms and their relations with the original matrix.   If the entries of the matrix are not from a mathematical structure which supports commutativity, what can we say about this problem?  P.S.: Please avoid using the transpose and/or inverse of a matrix. Basis of cotangent space Why do shell script comparisons often use x$VAR = xyes? I see this often in the build scripts of projects that use autotools (autoconf, automake).  When somebody wants to check the value of a shell variable, they frequently use this idiom:  if test "x$SHELL_VAR" = "xyes"; then ...   What is the advantage to this over simply checking the value like this:  if test $SHELL_VAR = "yes"; then ...   I figure there must be some reason that I see this so often, but I can't figure out what it is. Creating a unique alphanumeric 10-character string I'm looking to create a simple short-lived reservation system, and I'd like to generate confirmation numbers that are   unique random-looking alphanumeric short-ish, at least much shorter than 32 character-long strings returned by sha1   I'm only looking to have ~500 reservations, so I don't imagine high likelyhood of collissions.  One idea I had is generate an sha1 hash based on a date-time stamp and username, then truncating it to its first 10 characters.  Would something like that be reliably unique enough for the purposes of processing ~500 reservations? Why does gulp.src not like being passed an array of complete paths to files? Family name pluralization Making a Laser in Cycles - Straight Beam of Light? Resizing an Image without losing any quality Finite Series - reciprocals of sines Find the sum of the finite series $$\sum _{k=1}^{k=89} \frac{1}{\sin(k^{\circ})\sin((k+1)^{\circ})}$$ This problem was asked in a test in my school. The answer seems to be $\dfrac{\cos1^{\circ}}{\sin^21^{\circ}}$ but I do not know how. I have tried reducing it using sum to product formulae and found out the actual value and it agrees well. Haven't been successful in telescoping it. How can I shorten my command line (bash) prompt? How to select the nth row in a SQL database table?