Ubuntu server installation installing SSH
What's the difference between the server version and the desktop version?
Is colour, as represented using primary colours, accurate only to humans? Slightly biological, hopefully physical enough to be answered.  Suppose a magenta hue is represented by a mix of red and blue pigment. This is all very well for a creature with red and blue photoreceptors, but suppose it was seen by a creature which had a magenta-sensitive receptor, but no red or blue. Would the colour appear the same (insomuch as a qualititave concept can appear the same, I suppose I mean 'Would they interpret it as colour of the same wavelength?')?  The crux of my question is, do the particular bands in which photoreceptors are activated affect vision of additive, as opposed to pure, hues?  Finally, completely off-topic, but if there happens to be a biologist around, do animals on the whole have similar photoreceptors, or are they placed largely randomly?  Thanks, Wyatt Getting "Not found" message when running a 32-bit binary on a 64-bit system Is it safe to use the hash of the data as the key to encrypt them? Is it safe to use the hash of the data as the key to encrypt them?  That is, if I give one some encrypted data and tell them that the key that was used to encrypt them was the hash digest of the data before encrypting, will it be easier for them to decrypt them?  Edit as I can not reply to comments: The recipient will have the keys, that is no problem. I generated a key and copied it to my target:  ssh-keygen ssh-copy-id username@hostname   I left the the location of the key as default and did not set any passphrase.  For a small while after that, I was able to ssh username@hostname without being prompted for a password, and then it stopped working for some reason. Do I need an airport transit visa through Switzerland if I have no Schengen visa? Am traveling from Cairo to Moscow via Swiss Air I've been writing C and C++ code for almost twenty years, but there's one aspect of these languages that I've never really understood. I've obviously used regular casts i.e.  MyClass *m = (MyClass *)ptr;   all over the place, but there seem to be two other types of casts, and I don't know the difference. What's the difference between the following lines of code?  MyClass *m = (MyClass *)ptr; MyClass *m = static_cast&lt;MyClass *&gt;(ptr); MyClass *m = dynamic_cast&lt;MyClass *&gt;(ptr); Folland, "Real Analysis", Chapter 5.3, Exercise 36:     Let $\mathcal{X}$ be a separable Banach space and let $\mu$ be   counting measure on $\mathbf{N}$.  Suppose that   $\left\{x_n\right\}_1^\infty$ is a countable dense subset of the unit   ball of $\mathcal{X}$, and define $T \colon L^1(\mu) \to \mathcal{X}$   by $Tf = \sum_1^\infty f(n) x_n$.  (a)  $T$ is bounded.  (b)  $T$ is   surjective.   I have proved (a).  I would like help on (b).  Here are my ideas so far.    Say we want to show $y \in \mathcal{X}$ is in the image of $T$.  Reduce to the case $||y|| = 1$ and let $x_{n_m} \to y$.  My thought is to produce for each $N$ a function $f_N \in L^1(\mu)$ such that $||y - \sum_n^\infty f(n)x_n|| &lt; 1/N$ and also such that the $f_N$ converge in $L^1(\mu)$ to some $f \in L^1(\mu)$.  Then use the continuity of $T$ to conclude $T(f) = y$.    The way I have been setting up my inequalities is as follows. Pick $M_N$ such that for all $m &gt; M_N$, $||y - x_{n_m}|| &lt; 1/N$.  Then I want to define $f_N$ so that $$\sum_n^\infty f_N(n) = \sum_{m &gt; M_N}^\infty f_N(m) = 1, $$ hence $$||y - T(f_N)|| = ||\sum_{m &gt; M_N}^\infty f_N(m) y + \sum_n^\infty f_N(n)x_n|| \leq \sum_{m &gt; M_N}^\infty f_N(m) || y - x_{n_m} || &lt; \frac{1}{N}. $$  Presumably, if the $f_N$ are appropriately chosen, then I can find a dominating function and apply the Dominated Convergence Theorem to finish up.    However, getting all these hypotheses to hold simultaneously has been difficult.  In essence, the difficulty seems to be in requiring that the $f_N$ be "normalized" as well as possess a dominating function.  If this method is feasible, at least it seems to require a bit of analysis to show the desired series all converge.  Perhaps I am missing something cleaner.  If so, a simpler solution would be much appreciated.    -Thanks. When to use an object pronoun or a possessive adjective before a gerund The rule says that we can use a possessive adjective or an object pronoun before a gerund. Is there a rule  that says when to use each or are they interchangeable? Some say that it's wrong to use an object pronoun before a gerund. I remember that the main character is trying to find the group that destroyed his home planet while he was on a mission. His planet was very difficult to live on and the people became expert in martial arts and were the best soldiers in the galaxy. They were mercenaries and often helped against tyrants. There was a very memorable section in at least one book about an initiation task that the main character had to do in that he had to survive in their wilderness for days. He was at some point surrounded in a old building by thousands of poisonous worm/snake creatures that he managed to survive until rescued by the leaders. I am trying to fit a SVM to my data. My dataset contains 3 classes and I am performing 10 fold cross validation (in LibSVM):   ./svm-train -g 0.5 -c 10 -e 0.1 -v 10 training_data   The help thereby states:  -c cost : set the parameter C of C-SVC, epsilon-SVR, and nu-SVR (default 1)   For me, providing higher cost (C) values gives me higher accuracy. What does C in SVM actually mean? Why and when should I use higher/lower values (or the LibSVM given default value) of C? Is a path the set of points from a to b?  And is the stroke the "definition" (i.e. the color, shape, etc.) of the path?  And, how can you have a path with no stroke?  Is this only because it is a computer drawing program?  In the real world you can't have a path without a stroke can you?  If it matters, I am using Inkscape. How can I do development on my Android device? I have a pretty long commute to work and own an android phone. I figure it would be nice to do some simple programming on the way. I'm not picky on which language to code on. I usually have an internet connection on the train.  I've been looking through the android market but haven't found any apps that offer a "development environment" or an editor with a compiler. Is any development ON the Android possible? Does an app for this exist? How to show that $P(A\cup B) = P(A) + P(B) - P(A\cap B)$ Say we have a venn diagram with A on the left, intersection C in the middle and B on the right.   I want to show that $P(A\cup B) = P(A) + P(B)  - P(A\cap B)$  I know what it can be written as A+B+C, but a lot of the proofs  go from:  $P(A\cup B) = P(A) + P(B)  + P(C)$ to  $P(A) + P(B) = P(A\cup B)  + P(C) $  and then rearrange to  get the proof and get $P(A\cup B) =P(A) + P(B)-  P(C) $ . I just don't get how the left side of the inequality get go from $P(A\cup B)$  to $P(A) + P(B)$. Doesn't that only happen if we assume that they are disjoint. In this case, do we assume that they are disjoint? I know how to write the proof but just having a hard time actually understanding it. pgfplots and using axis cs to add points I am trying to mark two inflection points using a foreach loop in a pgfplot, but it isn't working.  \documentclass[tikz]{standalone} \usepackage{pgfplots} \pgfplotsset{compat = 1.10}  \begin{document} \begin{tikzpicture}   \pgfmathsetmacro{\infx}{1/sqrt(2)}   \pgfmathsetmacro{\infy}{exp(-.5)}   \begin{axis}[     xmin = -3,     xmax = 3,     ymin = -0.1,     ymax = 1.05,     domain = -4:4     ]     \addplot[blue, samples = 500, smooth] gnuplot {exp(-x^2)};      \foreach \x/\y in {\infx/\infy, -\infx/\infy}{       \draw[red] (axis cs: \x, \y) circle[radius = .025];     }   \end{axis} \end{tikzpicture} \end{document}   I am being told:  Undefined control sequence.^M &lt;argument&gt; axis cs: \x ^M                        , \y ^M l.34   \end{axis}^M Can I use Stack Exchange logos on a t-shirt or other apparel? I happened to notice while on the Super User site that one user's picture shows him wearing a shirt with the Super User logo on it. Interested, I wanted to find out where he got it from. Looking through old questions on Meta, I found out that there used to be a shop.stackexchange.com site that sold Stack Exchange gear. Unfortunately, they no longer sell any merchandise.  Is there any site where I can purchase a Stack Exchange site shirt/hat/etc.? If not, could I create a shirt/hat/etc. myself with one of the sites' logos on it? If so, where can I locate the logos in their largest size? Is Let us = Let's? Many times I heard these words interchangeably. I want to know if "Let's" and "Let us" are used for the same meaning.  I think (for me):   "Let us" is word used for requesting. Like Let us do something means requesting to allow us do something. "Let's" is words used for proposing. Like Let's play means proposing people to play. How to setup synctex with vim, pdflatex and an open-source PDF-viewer under Linux? I have a dataset with a large number of Yes/No responses. Can I use principal components (PCA) or any other data reduction analyses (such as factor analysis) for this type of data? Please advise how I go about doing this using SPSS. I've observed several incidents where users inadvertently posted detailed, sensitive information. For example, a Server Fault user who posted a question with working login credentials to his actual production server, or the Stack Overflow user who posted actual medical records as example data for his question.   What should be the procedure for handling such cases? Iterate two Lists or Arrays with one ForEach statement in C#