Yes, the books might have been written on this but not being a technical person, I'd like to understand in short and easy to understand language - How to interpret a histogram to know whether the photo is under or over exposed?
I realize that an image histogram is a graphical display of an images tonal distribution (i.e. horizontal darks to lights, vertical pixel distribution), but how does one really use it and why? I mean, can't you determine everything you need just by looking at the image?
403 error after upgrading to apache2.4 After upgrading from Ubuntu 13.04 server, the www pages won't display themselves.     Error 403 Forbidden You don't have permission to access / on this server.   I've changed access control saves from apache2.2 to apache2.4, but that didn't work. What else could I do? How to cleanup deadlinks I was reading some answers about ruby and there are a lot of links to _why's sites.  and took all his sites with him.  Almost every introduction question about ruby will include at least one or two links to one of his sites. Examples:          With a bit more effort I could probably find more questions with a lot of deadlinks.  My suggestion for discussion was, what would be a good way to solve deadlinks in the answers/comments? Not every site _why created has resurfaced somewhere else, but some could be replaced by new links.  But I wanted the discussion to go beyond this specific problem of deadlinks in the ruby answers, an automatic solution would be to let the links be scanned in a batch and when found dead be replaced by a google cache or webarchive version of the page, and perhaps mark it so that the community can replace the link with an alternative? Learning Insertion Sort in Ruby I have just started the MIT Introduction to Algorithms course through the material posted online. Along with the course I have also decided to learn/enhance my Ruby skills by coding the algorithms in it.   I am on the first algorithm given, which is Insertion sort, and I have the following code typed up but I am getting this error when I run it:     insertionsort.rb:5:in `>': comparison of Fixnum with nil failed (ArgumentError)   def  insertionsort(num) for j in 2..num.length     key = num[j]     i = j - 1     while i &gt; 0 and num[i] &gt; key         num[i+1] = num[i]         i = i - 1     end     num[i+1] = key end  puts num end  numbers = [23,34,46,87,12,1,66]  insertionsort(numbers)   I'm sure it is a fairly basic problem but I just can't grasp what it is at the moment. Any  help or tips would be very much appreciated. Let $f(z)$ be a holomorphic function on a disk of radius $&gt;1$ about the origin, and suppose that $|f(z)|\leq 1$ for $z$ with $|z|=1$ and $\text{Re}(z)&gt;0$ and $|f(z)|\leq 2$ for $z$ with $|z|=1$ and $\text{Re}(z)\leq 0$.  How does one show the bound $|f(0)|\leq \sqrt{2}$? Missing argument 2 for wpdb::prepare() Issue I'm having to update a WP installation for a community organisations from version 2.9.1 to the current 3.9.1.   The installation has a couple of custom built plugins that aren't documented.  I've just performed the WP version update and now I see a warning (Missing argument 2 for wpdb::prepare()) on every page that relates to the following line in the code of one of these custom built plugin:  $rows = $wpdb-&gt;get_results($wpdb-&gt;prepare("SELECT id, name FROM ".$table_name));   From what I've read online, this is due to a change in the coding, that requires 2 values to be sent to wpdb::prepare(), but I've no idea how the line of code given above, needs to be changed.  If someone could help me out, I'd really appreciate it. Reputation widget crash I have an issue with crashing reputation widget when it's added to the home screen. When I add it for the first time, it says "Please login before using this widget" (even though the app itself is logged in already). So I open the app, go back to the home screen, add the widget again and it crashes (and it's not added to the home screen). When I'll try to add it again, it says "Please login before using this widget" again. And then it just repeats - "Please login...", execute the app, crash, "Please login...", etc.  Restart of the device didn't make any change.  I have found .  My set up:  Stack Exchange app version: 1.0.89 Android version: 5.0.1 Device: Samsung Galaxy S4 "In back of'' vs. "back of" vs. the spatial sense of "behind" in AmE What is the ancestral form of language used in the fable that David was studying during the flight? David studies linguistics during the flight to LV-223. We get to listen and read a fable. Is it written in a real language? What is the name of the language? Can the fable be translated?  Approximate quotation:     hjewis jasma hwaelna nahast akwunsez dad'kta, tam ghermha vagam ugenthe Aligned equation which can break through pages I'm writing long sequences of aligned math equations, and LaTeX interprete them as single, unbreakable objects... which is Ok if the equation is nowhere near the end of the page.  Q: Is there a way to (automatically) break the align equation through pages?  In the code below,  \documentclass{report}                                                           \usepackage{amsmath}                                                             \usepackage{lipsum}                                                               \begin{document}                                                                 \lipsum[1-4]                                                                     \begin{align*}                                                                   FFFFFFFFFFFFFFFFFFFFFFFF &amp;= \partial_t(p)\\                                                               &amp;= \partial_t(m v)\\                                                             &amp;= m a\\                                                                         &amp;= m \dot{v}\\                                                                   &amp;= m \ddot{x}\\                                                                  &amp;= \partial_t(p)\\                                                               &amp;= \partial_t(m v)\\                                                             &amp;= ma\\                                                                         &amp;= m \dot{v}\\                                                                   &amp;= m \ddot{x}                                                                  \end{align*}                                                                     \end{document}      all of the equation goes to the second page. I do not want that  If I break manually, by closing the align and open another, I lose the alignment with the previous part.   \documentclass{report}                                                           \usepackage{amsmath}                                                             \usepackage{lipsum}                                                               \begin{document}                                                                 \lipsum[1-4]                                                                     \begin{align*}                                                                   FFFFFFFFFFFFFFFFFFFFFFFF &amp;= \partial_t(p)\\                                                               &amp;= \partial_t(m v)\\                                                             &amp;= m a\\                                                                         &amp;= m \dot{v}\\                                                                   &amp;= m \ddot{x}\\                                                                \end{align*}                                                                     \begin{align*}                                                                     &amp;= \partial_t(p)\\                                                               &amp;= \partial_t(m v)\\                                                             &amp;= m a\\                                                                         &amp;= m \dot{v}\\                                                                   &amp;= m \ddot{x}                                                                  \end{align*}                                                                     \end{document}   I do not want that either.  So far I read about breqn packages, but it seems not to do what I would like.  Any Suggestion?? Thx. What command can I type into the Terminal so that I can delete all .svn folders within a folder (and from all subdirectories) but not delete anything else? Conservation Of Angular Momentum of a falling stone I am currently stuck on the following question.   A stone is dropped from a stationary helicopter 500m above the ground, at the equator. How far from the point vertically below the helicopter does it land and in what direction? Solve this problem by conserving angular momentum.   My current interpretation is that when the stone falls in order to converse angular momentum the angular velocity must increase. This leads to the stone travelling to the east.   I equated the angular momentum at the start       L0=*(re+h)mVo  where re is radius of earth, h is the height above that, m is mass and Vo is inital velocity. To the angular momentum at any time  L=(re+h-1/2gt^2)m(Ve+Vo)  where the 1/2at^2 term comes from gravitational acceleration and Ve is the additional velocity.   I rearranged to find Ve and then integrated over the time it takes to fall the 500m in order to work out the extra distance the stone traveled. However, my answer is 1/2 what the answer should be. I have checked the maths and it seems to be fine. So I believe my set up is wrong. Any help would be appreciated. Currently my bibliography says "Literatur" (german). But I want something completely different there. How can I achieve that? An invalid argument, the conclusion of which is a tautology Why it is not possible to have such argument?  I found some textbook Introduction to Formal Logic and this is from one of the first excercises. This is marked as impossible, but I do not understand why. A friend asked me last week how to enumerate or list all variables within a program/function/etc. for the purposes of debugging (essentially getting a snapshot of everything so you can see what variables are set to, or if they are set at all). I looked around a bit and found a relatively good way for Python:   #!/usr/bin/python                                                                                                                                                                                                                            foo1 = "Hello world" foo2 = "bar" foo3 = {"1":"a",         "2":"b"} foo4 = "1+1"  for name in dir():     myvalue = eval(name)     print name, "is", type(name), "and is equal to ", myvalue   which will output something like:   __builtins__ is &lt;type 'str'&gt; and is equal to  &lt;module '__builtin__' (built-in)&gt; __doc__ is &lt;type 'str'&gt; and is equal to  None __file__ is &lt;type 'str'&gt; and is equal to  ./foo.py __name__ is &lt;type 'str'&gt; and is equal to  __main__ foo1 is &lt;type 'str'&gt; and is equal to  Hello world foo2 is &lt;type 'str'&gt; and is equal to  bar foo3 is &lt;type 'str'&gt; and is equal to  {'1': 'a', '2': 'b'} foo4 is &lt;type 'str'&gt; and is equal to  1+1   I have so far found a partial way in PHP (courtesy of ) but it only lists all variables and their types, not the contents:   &lt;?php // create a few variables $bar = 'foo'; $foo ='bar'; // create a new array object $arrayObj = new ArrayObject(get_defined_vars()); // loop over the array object and echo variables and values for($iterator = $arrayObj-&gt;getIterator(); $iterator-&gt;valid(); $iterator-&gt;next())         {         echo $iterator-&gt;key() . ' =&gt; ' . $iterator-&gt;current() . '&lt;br /&gt;';         } ?&gt;   So I put it to you: how do you list all variables and their contents in your favorite language?    Edit by : I propose this question follows the spirit of a little "". If you do not agree, just edit and remove the tag and the link. Which is the best way to put function plots into a LaTeX document? The Equation $11^x + 13^x + 17^x =19^x  $  Has    No Real Roots Only One Real Roots Exactly Two Real Roots  More than Two Real Roots    What I have done is   The function $f(x)=11^x + 13^x + 17^x -19^x  $ is strictly increasing and being always positive it have no roots What is a serialVersionUID and why should I use it? Eclipse issues warnings when a serialVersionUID is missing.       The serializable class Foo does not declare a static final   serialVersionUID field of type long   What is serialVersionUID and why is it important?  Please show an example where missing serialVersionUID will cause a problem. Show/Hide  dropdown, with jQuery, based on value I am currently writing an academic text and need to directly quote/cite text from a paper. What is best practice when I need to add a remark/note to the quote?  For instance, I would do it like this: The authors claim that "we do the best work ever in the area of CS (note: Computer Science)".  So in the above case the actually quoted text is "we do the best work ever in the area of CS", however, I want to add a note which explains the abbreviation "CS".  How should this be done?  Related questions: How do I check which shell I am using? I read that terminal is nothing but shell, and Unix provides different flavors of shells:   Bourne shell (sh) C shell (csh) TC shell (tcsh) Korn shell (ksh) Bourne Again shell (bash)   Questions:   When I open a terminal window, which shell is opened by default? How do I check how many shells are installed? How do I change the shell used from my account?