Why can $R^2$ be negative in a multiple regression that doesn't have an intercept ($\hat{\beta}_0 = 0$)?
Negative R squared contradicts ssa/sst?
Passing an array as a function parameter in JavaScript I've been doing some practice questions in the textbook for an upcoming predicate calculus lecture and I think I've managed to get A and B (possibly C) correct but I am clueless on how I can manage D and E.   For A I got: ∃x(R(x)∧¬B)  For B I got: ∀x(¬R(x)∧B)  For C I got: ∃x(R(x)∧(x=y))   - Not sure if this is even remotely correct    R(X) : ”X is rich”  X = Y : ”X equals Y”  B : ”Bill Gates”  a) Someone besides Bill Gates is rich.  b) Bill Gates alone is rich.  c) At least two people are rich.  d) Exactly one person is rich.  e) Exactly two persons are rich.  The universe of discourse is the set of all people. At the moment, I have created a code that retrieves data from the database and displays it. However, for some reason, I cannot see the files I want to retrieve on my page. My goal is that the data gets retrieved from the database, and is displayed on the webpage. I do not need to make a connection with the database since Wordpress does that automatically.  My code:  &lt;?php  global $wpdb; // this adds the prefix which is set by the user upon instillation of wordpress $table_name = $wpdb-&gt;prefix . "wpex_programma"; // this will get the data from your table $retrieve_data = $wpdb-&gt;get_results( "SELECT * FROM wpex_programma; " ); print_r($retrieve_data); ?&gt; &lt;ul&gt; &lt;?php foreach ($retrieve_data as $retrieved_data){ ?&gt; &lt;li&gt;&lt;?php echo $retrieved_data-&gt;column_name;?&gt;&lt;/li&gt; &lt;li&gt;&lt;?php echo $retrieved_data-&gt;another_column_name;?&gt;&lt;/li&gt; &lt;li&gt;&lt;?php echo $retrieved_data-&gt;as_many_columns_as_you_have;?&gt;&lt;/li&gt; &lt;?php  } ?&gt; &lt;/ul&gt;   My question: the data is not shown and I believe it is not retrieved. How can I fix that? The table name is correct, and I have data in my database tabel. The print_r($retrieve_data)returns the following: Array ( [0] =&gt; stdClass Object ( [id] =&gt; 35 [naam] =&gt; /public_html/wp/wp-content/plugins/AbonneerProgrammas/FilesUpload/Country Kickin 1.mp3 ) )  My query log:    My database structure:   New:  &lt;?php  global $wpdb; // this adds the prefix which is set by the user upon instillation of wordpress $table_name = $wpdb-&gt;prefix . "wpex_programma"; // this will get the data from your table $retrieve_data = $wpdb-&gt;get_results( "SELECT * FROM wpex_programma; " ); print_r($retrieve_data); ?&gt; &lt;ul&gt; &lt;?php foreach ($retrieve_data as $retrieved_data){ ?&gt; &lt;li&gt;&lt;?php echo $retrieved_data-&gt;id;?&gt;&lt;/li&gt; &lt;li&gt;&lt;?php echo $retrieved_data-&gt;naam;?&gt;&lt;/li&gt; &lt;?php  } ?&gt; &lt;/ul&gt; Every time I install a new Linux kernel, it gets left in the grub_config, making the boot menu longer each time.    I know I can manually search through the installed packages and remove them.  Does Ubuntu provide any easier way to clean them up or keep them from showing in the boot list? Can black holes form in a finite amount of time? What does "if not" mean in the given sentence 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? When does $120$ divide $n^5 - n$ Find n such that $n^5 - n$ is divisible by $120$. (*Here $n$ belongs to the natural number set)  Seems a trivial problem, but the answer mentioned in the text book seemed incomplete to me so I'm here just to ensure whether approach to this problem is correct or not.  So my approach is as follows: We know that $n^5 - n$ can be written as $n^5-n = n(n-1)(n+1)(n^2 + 1)$  Now since it's product of three consecutive natural numbers so it's divisible by $3! = 6$. Now using Fermat's Little theorem we can prove that $n^5= n \mod5$ hence $n^5 - n$ is divisible by $5$ as well. So $n^5 - n$ is divisible by $30$. Now to ensure their is another factor of $4$ in the term we need to ensure that $n^5 - n$ is divisible by $8$. I found that all odd natural numbers and multiples of $8$ makes $n^5 - n$ divisible by $8$, hence $n^5 - n$ is divisible by $120$. But in the text book they have only mentioned odd natural numbers as answer, which seemed incomplete to me.  Thanking everyone in advance:P German language: use of comma in numbers Error with \newcommand using \multicolumn in table I want to define a new command \tableheadline that (1) formats the headline text in some way and (2) takes an optional argument for spanning multiple columns while centering the headline.  I tried the following implementation:  \documentclass{minimal}  \newcommand{\tableheadline}[2][1]{\multicolumn{#1}{c}{\textit{#2}}} % \newcommand{\tableheadline}[2][1]{\multicolumn{1}{c}{\textit{#2}}}  \begin{document}   \begin{tabular}[\textwidth]{cc}      \tableheadline[2]{C}     \tableheadline{A} &amp; \tableheadline{B} \\     0 &amp; 1 \\     2 &amp; 3 \\   \end{tabular} \end{document}   This, however, gives me an error:  ! Misplaced \omit. \multispan -&gt;\omit                    \@multispan l.8 \tableheadline[2]{C}   I also get the error when I do not even use the optional argument (see commented line in the MWE). Any ideas what I am doing wrong? "Add" button doesn't work with JavaScript off I'm using stackoverflow.com with JavaScript off. I accept this comes with somewhat less functionality, however for the most part SO works fine.  If I look at the home page (), every single button on there except for two types works with JS off.  The first second is that the "x Votes; y answers;z views" mouse-over indicates they're links but clicking them does nothing. This one is less of an issue because the user can still click the question title, and they're only implied buttons anyway.  The second (and bigger) issue is the "Add" buttons next to "Favorite Tags" and "Ignored Tags". These are explicit buttons that don't do anything with JS off. There is no working JS substitute for them (the "tag subscriptions" link itself works, but the page it goes to doesn't work with JS off, but that's another bug report). How to urlencode data for curl command? How do I ensure a piece of code runs only once? Proof of -(-v)=v in a vector space The exercise is: Prove that $-(-v)=v$ for every $v \in V$  Proof Suppose  $v \in V$ and $V$ is a vector space. Then $-(-v) \in V$ as result of the scalar multiplication property and $-(-v)=-(-1\cdot v)=-1 \cdot(-1\cdot v) =(-1 \cdot-1)\cdot v = 1 \cdot v = v $ The desired result $-(-v)=v$ holds.  The solution manual gives the proof:  Proof   I just wanted to make sure that the way I did the proof isn't missing anything?Thanks The shop is five minutes away.     According to the dictionary, away is an adverb. An adverb modifies a verb. In the above example, what word does away modify? Why is away not an adjective?       The shop is five meters tall.     tall is an adjective in the second example. It modifies five meters (does it?). So why is away an adverb? Correlations with unordered categorical variables I have a dataframe with many observations and many variables. Some of them are categorical (unordered) and the others are numerical.  I'm looking for associations between these variables. I've been able to compute correlation for numerical variables (Spearman's correlation) but :   I don't know how to measure correlation between unordered categorical variables. I don't know how to measure correlation between unordered categorical variables and numerical variables.   Does anyone know how this could be done? If so, are there R functions implementing these methods? How can I open a text file with TextWrangler from the Terminal (command line)? percent signs in luacode* environment (LuaLaTeX) Can someone explain what happens here:  \documentclass{article} \usepackage{luacode} \begin{document}  \begin{luacode*} tex.print("xx\%a","yy\\%b","zz\\\%c") \end{luacode*}  \end{document}   The result is xxyy%b zz%c. (The xx,yy,zz is clear.) The \%a is "ignored", the \\%b and the \\\%c results in the "same" %b (or c). What is the preferred way to get a % in the PDF output? Why is the \%a ignored? What does TeX see after returning from the lua call? How large would the steam explosion at Chernobyl have been? So the  of the HBO series began to cover the  that led to them sending three divers into the water below the reactor to drain the tanks.  This occurred after the initial explosion that destroyed the reactor, and after the fire in the core had been put out. But at this point the decay heat and remaining fission reaction kept the core at more than 1200°C, causing it to melt through the concrete floors below the reactor.  And below the reactor were water tanks which contained 7,000 cubic meters of water (according to the TV show. If anyone has a real figure, I'd love to hear). When the lava of the melted core hit it, it would cause an enormous .  Finally, my question: About how large would this explosion have been? The character in the show says "2-4 megatons" (of TNT equivalent, I assume). I'm pretty sure this is absurd and impossible. But real estimates are hard to come by. Other sources vary wildly, some repeating the "megatons" idea, and others saying it would've "". This still seems crazy.  tl;dr:  I know a lot of it hinges on unknowns and the dynamics of the structures and materials involved, so I can simplify it to a constrained physics question:  Assuming 7,000 cubic meters of water instantly flashes to steam, how much potential energy is momentarily stored in that volume of steam occupying the same volume as the water did?  I don't know what to assume the temperature of the steam is. There were hundreds of tons of core material at temperatures near 1200°C, so worst case scenario you could assume all the steam becomes that temperature as the materials mix. Best case scenario, I guess we could assume normal atmospheric boiling point (100°C)? How to run test methods in specific order in JUnit4?