ArrayList.get() returns pointer not value?
Is Java "pass-by-reference" or "pass-by-value"?
Way to detect frozen video with ffmpeg? Is there a way to detect frozen video with ffmpeg? I only need to know if there are rather large regions of frozen video, say 10 seconds or more.   I'm familar with the  filter.   Maybe you could first difference adjacent frames, then use blackdetect to tell whether the difference has not changed? I'm not sure how to perform the difference though. First post review queue: answers are questions, questions are answers I believe there is a typo in the  review queue. When reviewing a question, the information message asks the user to review the answer. Take a look at the image below.    Similarly, when an answer is posted in the queue, the description box calls it a question instead. Has anyone else noticed this? Gravitational waves and time Two questions.  It is said that time can only go slower in gravity fields and if you move faster.  I have heard that when a gravitational wave pass earth then the space/time vibrate and time change for an instance.  But a wave is often with a top and a valley.  They have now atomic clocks that might be able to detect time variations, placed in satellites around the sun and "quantum entangled". "Using Atomic Clocks to Detect Gravitational Waves"   So what if we could compare time ticks between clocks in space at "absolute frame of reference" where time has its maximum universal speed as time in deep space between Galaxy Filaments.  Will we only detect that time ticks slower for an instance when the gravational wave pass?  1. Or will we detect that time tick slower AND faster than normal time also, as compared to zero gravity time and no movement time in "absolute frame of reference"?  2. Can time go let's say 10 times faster by theory/mathematics, by a extreme theoretical gravitational wave, than time in "absolute frame of reference time"? Is it safe to answer "erase disk and install Ubuntu" on a virtual machine? Why are angles dimensionless and quantities such as length not? So my friend asked me why angles are dimensionless, to which I replied that it's because they can be expressed as the ratio of two quantities -- lengths.   Ok so far, so good.  Then came the question: "In that sense even length is a ratio. Of length of given thing by length of 1 metre. So are lengths dimensionless?".   This confused me a bit, I didn't really have a good answer to give to that. His argument certainly seems to be valid, although I'm pretty sure I'm missing something crucial here. connectedness of uniform topology How can i change formatting of the table of contents to avoid section numbering and section title to overlap?  Document:  \documentclass[10pt,oneside,notitlepage]{book}  % Use Heuristica Font \usepackage{heuristica} \usepackage[heuristica,vvarbb,bigdelims]{newtxmath} \renewcommand*\oldstylenums[1]{\textosf{#1}}   \begin{document}  \tableofcontents  \part{Part one}  \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh} \chapter{Chapter Oh}   \section{Chapter Hi} \section{Chapter Hi} \section{Chapter Hi} \section{Chapter Hi} \section{Chapter Hi} \section{Chapter Hi} \section{Chapter Hi} \section{Chapter Hi} \section{Chapter Hi} \section{Chapter Hi}  \end{document}   Example output: Finitely generated monoids- axiomatization- compactness theorem. The set that only contains itself I was just wondering since i have the 12.04 lts ubuntu edition if it's possible to upgrade it to 13.04 or even 14.04 after it gets released without losing any of my files and installed apps?  That's actually the main reason i chose the LTS version because i didn't know if i had to re-install all my apps every time a new ubuntu version gets released. What does --shell-escape do? I stumbled upon an example, which needed to be compiled with the additional option --shell-escape. Using this option it worked just fine, but I'm curious:     Why or when is this option needed and what does it actually do? The first and (the) second chapter(s) are difficult - which is correct? Automatically open ICS files in Google Calendar Prior to doing some benchmarking work how would one free up the memory (RAM) that the Linux Kernel is consuming for its buffers and cache?    Note that this is mostly useful for benchmarking. Emptying the buffers and cache reduces performance! If you're here because you thought that freeing buffers and cache was a positive thing, go and read . The short story: free memory is unused memory is wasted memory. Transforming multiple rows into a single row Why are NginX and Lighttpd not affected by Slowloris? I am investigating the vulnerability to  and I think I understand how and why this sort of attack works.  What I don't understand is why Lighttpd and NginX are not affected (according to the same article as linked above). What do they make so different? Import Large Excel File Verifying that the ideal $(x^3-y^2)$ is prime How to prove that the ideal $I=(x^3-y^2)$ in $k[x,y]$ is prime?    I have constructed a map from $k[x,y]$ to $k[t]$, which maps $x$ to $t^2$, and $y$ to $t^3$. Then, I want to show that the kernel is exactly $I$. But the difficulty is that how to prove the kernel is contained in $I$.  Could you help me? Thanks a lot! Birthday problem: why is this solution wrong? This question is about the birthday problem: the probability that in a group of n people, at least two of them have the same birthday ().  An easy way to calculate the probability is to calculate first the probability that no two people have the same birthday.  Let's say that I want to calculate the probability that in a group of 20 people, NO two people have the same birthday.  So, for 20 people with different birthdays, I can choose the first birthday in 365 ways, the second in 364 ways and so on, while for 20 people who can have the same birthday, I can choose the first birthday in 365 ways, the second also in 365 ways, and so on. At the end:  $p={365 \cdot 364 \cdot 363 \cdot ... \cdot 346 \over 365 \cdot 365 \cdot 365 \cdot ... \cdot 365}\approx 0.59$  This is the right method and I understand it. I don't understand why the following method is wrong:  The probability that in a group of 20 people NO two people have the same birthday is the ratio between the combination without repetition of 20 birthdays and the combination with repetition of 20 birthdays:  $$p={C_{365,20} \over C'_{365,20}}={\binom{365}{20} \over \left(\binom{365}{20}\right)}={\binom{365}{20} \over \binom{365+20-1}{20}}=\frac{{{365!}\over {20!\cdot(365-20)!}}}{{(365+20-1)!}\over{20!\cdot{(365-1)!}}}\approx 0.35$$  I understand the mistake is in the denominator (as the numerator is the same of the other method, after simplifying that 20!), but why? Isn't it right to calculate the k-combination with repetition of 20 birthdays?  Thanks for helping! Why does the order of parameters matter for sp_trace_create?