I am using a VPS from Contabo.com, and when using Digitalocean, I didn't have any problems. Now, when trying to install courier-authdaemon, I get an error saying that the package could not be found. Does anybody knows how to solve this problem?
How do I get to the Universe Repository in supported versions of Ubuntu?
Physically Identify the failed hard drive Find a function $f: \mathbb{R} \to \mathbb{R}$ that is continuous at precisely one point? Is the function $f(x) = \lim_{k \to +\infty} \tan{kx}$ a right example?  But I do not know whether this is a function at first. Is this a function?  Could you give a correct real-valued function that is continuous at precisely one point?  Thanks. Getting command-not-found working under zsh What does the register keyword do in C language?  I have read that it is used for optimizing but is not clearly defined in any standard.  Is it still relevant and if so, when would you use it? Rough Smart objects problem in Photoshop I am using Adobe CC(2015) latest version and the behaviour of the smart objects isn't normal. When I paste a vector from Illustrator to Photoshop, the vector looks low quality or rough.   ORIGINAL  IN PHOTOSHOP   However, if I click over the smart object layer(in Photoshop)and this is opened in Illustrator, the vectors looks as the original one.   VECTOR OPENED IN ILLUSTRATOR FROM PHOTOSHOP SMART OBJECT   How can I solve this? How should I invest my money as a young graduate in Europe? This is related to this , but that question's answers are 95% tailored for residents of the US, basically recommending to full out the 401k retirement plan and this and that about stock market investments. My question is, are there other types of investments that are good for a young person starting out a career? Pointers:  I live in a welfare state in Europe, so I don't have college debt, (debt of any kind actually). Rainy day funds are much less needed than in the US, since here there is unemployment insurance for at least 18 months. I can probably invest 500€-600€ monthly for something. (The question is what.) I am not looking to invest in my retirement (I am already forced to pay for that out of my salary). I want to maximize my earnings for medium term (5-15 years). I specially want to avoid the typical paradox of (be poor in your 20's,30's,40's and be able to use your money after your 50's). That is not an option for me, I want to use my money for X or Y. But the money used has to be earned from an investment. That is a general rule for me.  For example I want to earn from my investments at least 70k€ after 5-10 years. So I'm guessing this would be a high risk investment, correct? I would like to spend on travel, on courses, on sports etc... But I insist that the money I spend should be a result of an investment not from my salary. Additionally I am not looking to buy a house so I don't want a mortgage. Except if this would constitute a good investment? FYI: this applies to France. But I'd like a general answer so others can benefit. If the question is unclear, a duplicate or off-topic don't hesitate to comment How to change value of ArrayList element in java Is the sorting algorithm used by .NET's `Array.Sort()` method a stable algorithm? Is the sorting algorithm used by .NET's Array.Sort() method a  algorithm? Is it wasteful to use a heating element, instead of doing useful work? Consider a computer CPU consuming electrical energy to perform calculations and consequently emitting heat.  Assumption: That a CPU consuming x Watts of power, emits the same amount of heat as an incandescent heating element which consumes the same amount of power.  The rest of the question assumes that this is true: the energy has to go somewhere, and I can't see that the outcome of the calculations counts as "somewhere".  I've long repeated the claim that "wasteful" appliances such as incandescent lightbulbs, over-full kettles, computers left running, etc. are not wasting power if we make the assumptions:   the appliance is in a room which we aim to maintain at above a certain temperature, warmer than the external temperature (cf a home in winter) the room leaks heat to the outside faster than the "wasteful" appliances emit heat. the room contains an electric heater the electric heater is regulated by a thermostat   In these circumstances, I think (?), if a light bulb produces excess heat, its only effect is to cause the thermostat to switch off sooner, so what energy you've "wasted" in the light bulb, is "saved" at the heater.  I don't think that's controversial.  But my question is:   If a CPU does useful work, and emits all the input energy as heat as a side effect But a heating element emits the same heat, without doing useful work Is it therefore wasteful to use heating elements? Is it more efficient to (for example) run  on a CPU, to get "free" computation as a side-effect of heating?   One reason to heat a room with a heating element, rather than with CPUs, is that the heating element is much cheaper to produce. But ignoring the initial cost of the hardware, would a "heater" made out of 20 CPUs, each running at full capacity and consuming 50W each, output less thermal heat than a 1KW element that does nothing else useful?  To be useful, of course, the CPUs would need to output the result of their computations, which would account for a tiny amount of energy. Let's assume that's negligible.  I'm sure there's a flaw in there somewhere; probably that the assumption above is false. What have I missed? Equivalent Definitions of the Operator Norm How do you prove that these four definitions of the operator norm are equivalent? $$\begin{align*} \lVert A\rVert_{\mathrm{op}} &amp;= \inf\{ c\;\colon\; \lVert Av\rVert\leq c\lVert v\rVert \text{ for all }v\in V\}\\ &amp;=\sup\{ \lVert Av\rVert\;\colon\; v\in V\text{ with }\lVert v\rVert\leq 1\}\\ &amp;=\sup\{\lVert Av\rVert\;\colon\; v\in V\text{ with }\lVert v\rVert = 1 \}\\ &amp;=\sup\left\{ \frac{\lVert Av\rVert}{\lVert v\rVert}\;\colon\; v\in V\text{ with }v\neq 0\right\}. \end{align*}$$ I have multiple Ubuntu machines at home and a pretty slow internet connection, and sometimes multiple machines need to be updated at once (especially during new Ubuntu releases.)  Is there a way where only one of my machines needs to download the packages, and the other machines can use the first machine to get the debs?  Does it involve setting up my own local mirror?  Or a proxy server?  Or can it be made simpler? Using fflush(stdin) Get the newest file from directory structure year/month/date/time I store backups of databases in a directory structure  year/month/day/time/backup_name  an example would be   basics_mini/2012/11/05/012232/RATIONAL.0.db2inst1.NODE0000.20110505004037.001 basics_mini/2012/11/06/012251/RATIONAL.0.db2inst1.NODE0000.20110505003930.001  note that timestamp from the backup file cannot be used. Before the automation testing starts the server time is set to 5.5.2011  So the question is how I can get the latest file if I pass the "base directory" (basics_mini) to some function that I am going to code.  I need to restore the newest database. I do that in php but I wonder if there is a simple shell scripting solution. Why do some questions in question lists have a yellow background? On SO, when I'm scrolling through "questions" some have a yellow background.  Is this intuitive to everyone but me?  What is the yellow background trying to tell me about this particular question? Portable Ruby on Rails environment I got myself a new 8 gig USB key and I'm looking for a decent solution to have a portable RoR environment to learn on. I did the google on it and found a few possibilities, but I'm curious to hear some real life experiences and opinions. Thanks! No analytic function in $\{|z|<1\}$ such that $f(0)=1$ and $|f(z)|\ge 1+|z|^2$. Proof strategy Show there is no analytic function in $\{|z|&lt;1\}$ such that $f(0)=1$ and $|f(z)|\ge 1+|z|^2$. I guess something went wrong along the way and I would like your assistance.   $f$ does'nt get a maximum in the domain, because if it did, it would be constant in the domain, meaning $|f(z)|=1\ge 1+|z|^2$ which doesn't hold for all z. Since $f$ isn't zero in the domain, ${1\over f}$ is analytic in the domain. but $|{1\over f(z)}|\le {1\over 1+|z|^2}\le 1={1\over f(0)}$, which indicates a local maximum making ${1\over f}$ constant, contradiction the fact the $f$ isn't. What am I really lacking here? One-dimensional vector space and it's subspaces Units in gravitational $N$ body simulations Temperature in space Temperature is a measure of kinetic energy transferred to particles, henceforth,  being vacuum, temperature cannot be measured. But then, there is cosmic background radiation. It is the leftover heat from the Big Bang, but then heat in space doesn't make sense, how does this radiation, heat up space time when it technically cannot be heated up? Moreover why is it referred to as heat when it is approximately just $2.5$ Kelvin, which is just above absolute zero? What's the derivative of: $ \sqrt{x+\sqrt{{x}+\sqrt{x+\cdots}}}$? let $ y=\displaystyle \sqrt{x+\sqrt{{x}+\sqrt{x+\cdots}}}$, i'm really interesting to know how do I find :  $\displaystyle \frac{dy}{dx}$ ?.  Note: I have used the definition of derivative of the square root function but i don't succed .  Thank you for any help