How to access global variable inside method in Java?
What is a NullPointerException, and how do I fix it?
How Do I Allow A Standard User to Install Programs? Can't boot without Flash Drive plugged in 3-4 old computers = general purpose cluster? Unable to locate package lib32bz2-1.0 I am trying to install Simplicity studio on Ubuntu 15.04 (64-bit) and I get this error  E: Unable to locate package lib32bz2-1.0 E: Couldn't find any package by regex 'lib32bz2-1.0'   I tried to install lib32bz2-1.0 package, again I get the same error. How to install package lib32bz2-1.0 on Ubuntu 15.04(64-bit) How do you express that your understanding of something is completely changed? When something blows your mind and changes your understanding of something that you've believed in for years, how do you express it (formally or informally)? Inner join vs Where Is there a difference in performance (in oracle) between  Select * from Table1 T1  Inner Join Table2 T2 On T1.ID = T2.ID   And  Select * from Table1 T1, Table2 T2  Where T1.ID = T2.ID   ? Would the latter be an issue with the funding body, when the project proposal and budget only covers the expenses for hiring one postdoc? Note: it is the supervisors who got the grants, not the postdocs themselves. Keeping an updated balance (Accounting) I have been struggling trying to find a way to properly and reliably maintain a balance for accounts in an order/payment system.  Currently, the process consists of three tables. Below example is very simplified but gets the point across.  Table one contains the account ID, name, total paid, total orders, balance etc.  Table two contains payments, date, the account ID (FK) and amount.  Table three contains orders, date, the account ID (FK) and amount.  Calculating the balance is of course as easy as  SELECT SUM(payments.AMOUNT) FROM payments WHERE ID = [account] SELECT SUM(orders.AMOUNT) FROM orders WHERE ID = [account]   Followed by some simple addition/subtraction math:  UPDATE accounts SET BALANCE = [balance] WHERE ID = [account]   All good - the problem is - how do I maintain this over let's assume years of activity and many, many transactions?  Currently the accounts table is updated every single time a transaction is made, meaning the above three statements run every time. There is of course an index on the ID column in all three tables, and everything is fast and neat for now, but I work with less than 100,000 transactions, meaning everything fits into the RAM and basically all I throw at the database gets executed immediately. Over time this will change, of course - so how do I handle this?  Is it better to mark the accounts as "dirty" and process balancing in a batch job later, or can I keep updating the balance real-time even when I reach the point where the orders and payments tables will not fit into the RAM?  Do I need to segment the orders and payments and "lock" everything before a given time, such as before last calculation? (I would rather not). I ask because then I could do a SUM WHERE DATE > [last lock timestamp] and update with UPDATE BALANCE = [balance] + [value for last lock] and prevent the problem from outgrowing resources.  I don't need a running balance for each transaction. That's all I can find results for when I try to research this problem. I just care about the total amount paid, the total amount ordered and the balance of accounts.  Why don't I calculate on the fly when I need the balance, you ask? Because one must be able to query the system and ask "Which of my (let's say) 50.000 accounts have a balance below 0?" - something we cannot do easily if we do not store the balance with every account. If $k=1$, we have \begin{align} \sum_{n\ge1}\frac{1}{\binom{2n}{n}}&amp;=\frac12\sum_{n\ge1}n\mathrm{B}(n,n)\\ &amp;=\frac12\int _{0}^{1}\sum_{n\ge1}n(t-t^2)^{{n-1}}{\mathrm  d}t\\ &amp;=\frac12\int _{0}^{1}\frac{1}{(t-t^2-1)^2}{\mathrm  d}t\\ &amp;=\frac13+\frac{2\sqrt3\pi}{27} \end{align} I wonder if there exists a general formula of $\sum_{n\ge1}{\binom{2n}{n}^{-k}}$ with $k\in\Bbb N^*$. This may involve some ${}_pF_q$ functions. If an opponent casts  to gain control of  then sacrifices it who will draw the card? Generator of rational functions unchanged under $\sigma(X) = X + 1$ Let $L = K(X)$ be the field of rational functions over a field $K$ with characteristic $p &gt; 0$, and let $\sigma \in \operatorname{Aut}_K(L)$ with $\sigma(X) = X + 1$.   Show that $G = \left&lt;\sigma\right&gt;$ is finite, and determine a generator of $L^G = \{ f \in L: \rho(f) = f$ for all $\rho \in G \}$ over $K$.    My solution so far: $G = \left&lt;\sigma\right&gt;$ is finite because char $(K) = p &gt; 0$ and therefore $\sigma^p (X) = X + p = X $.  A rational function unchanged under $\sigma$ will also be unchanged under any $\sigma^n$, so we don't have to worry about powers of $\sigma$ I think.   Any ideas for finding a generator? Thanks. Do any open-source .Net libraries (commercially usable) exist for reading/writing LiDAR data? I have a few LiDAR point data (.las files) with me. I would like to read the X,Y and Z from it using .Net. I found , which is in C++ and I am not sure if it can be used commercially after reading the licensing information. Has anyone found any good ones? How do I backup all files? (.dbus and dconf backup problems) What are /home/user/.cache/dconf and /home/user/.dbus? Why does their backup fail?  I tried following  (see code below) but while it allowed me to backup the above files, now I am told it couldn't backup /home/[user]/.dbus/session-bus.    $ man chown $ sudo chown user .cache/dconf   [sudo] password for user:  $ sudo chown user .dbus $ man chgrp $ sudo chgrp user .cache/dconf $ sudo chgrp user .dbus   How do I fix it so it will not take my time closing an error message after each backup? Should I exclude these folders ? Why are they not needed? Why would someone want to back them up? What should I do when a hacker gives me hacked money? I was peacefully playing GTA Online (yeah, was killing someone coming out of ls customs) then a hacker came and killed me using explosive ammos, I called him a hacker and he teleported to me and gave me 790k. I know that people get banned for receiving this kind of money, what should I do to avoid the ban? Converse of Schur's Lemma in finite dimensional vector spaces I am trying to prove (or disprove) the converse of Schur's Lemma in finite dimensional vector spaces. I am not sure if it holds in this case, but I have tried to apply the idea that proves it in representation theory (see for example Theorem 4.3  that uses Maschke's theorem or in questions  and ).  The converse of Schur's Lemma in finite dimensional vector spaces is:     Let $V$ be a finite dimensional vector space over the complex numbers. Let $S$ be a set of endomorphisms of $V$ and assume that every endomorphism $A$ of $V$ such that $$AB=BA\text{ for all }B\in S$$ is of the form $\lambda I, \ \lambda\in\mathbb{C}$. Then $V$ is a simple $S$-space.   (*an endomorphism of $V$ is a linear operator from $V$ to $V$  *$V$ is a simple $S$-space if the only $S$-invariant subspaces of $V$ are $V$ itself and the zero subspace)  What I've tried so far:  Assume to the contrary that $V$ is not a simple $S-$space. Then, there exists a subspace $W$ of $V$ such that $W\not =\{0\}$, $W\not= V$ and $W$ is $S$-invariant. Let $W'=V\setminus W$. Then, since $V$ is finite, we can easily prove that $V=W\oplus W'$ (this is my attempt to translate Maschke's theorem in vector spaces). Consequently, for every $v\in V$, there exists unique $w\in W$ and $w'\in W'$, such that $v=w+w'$. Define the projection $P:V\rightarrow V$ by $Pv=w$ for every $v\in V$.   What is left to prove is that $PB=BP$ for all $B\in S$. Then $P$ is clearly not a scalar and thus we have the contradiction we are looking for.  There is a difficulty in showing that $PB=BP$ for all $B\in S$, because $W'$ might be $S$-invariant or not. More precisely:   Let $v\in V=W\oplus W'$ and $v\not =0_V$.  If $v\in W$ then $Bv\in W$ because $W$ is $S$-invariant, therefore: $PBv=Bv$ and $BPv=Bv$.  If $v\in W'$ then $Pv=0$, hence $BPv=B\cdot 0=0$, and  (i) if $Bv\in W'$ then $PBv=0$.  (ii) if $Bv\in W$ then $PBv=Bv$ and this is where the problem occurs.  Any hints, ideas or counterexamples would be very helpful. Definite article, repetition in lists Which would be correct?        The fridge, the shelves, the walls, the floor, and John himself, were all covered in foam.   The fridge, shelves, walls, floor, and John himself, were all covered in foam.      The the can be applied to all the nouns, so is there a need to repeat it? Custom action to set emblem in thunar What does the explicit keyword mean? What does the explicit keyword mean in C++? Do animagi get to pick their animal? Say that I want to become an Animagus, and am really hoping to be a certain animal (say, a stag). I study a whole bunch and manage to perfect the technique. Do I get to pick the animal I wind up as, so that I wind up being a stag like I want? Or is it something where I just find out what I turn into (and if I wind up as a dung beetle, tough luck)?    This is not a duplicate of  because that question is about which animals an Animagus can potentially transform into. Mine is about if I can decide which potential animal I wind up being. General Relativity Equivalence Is Einsteins Equivalence theorem in General Relativity correct? It seems to me that it neglects the fact that gravitational acceleration depends upon separation distance squared, thus neglecting the effect of tidal forces.   For example, as I sit on earth, I experience the affect of earth's gravity; Although the acceleration on my head is slightly less than the acceleration acting on my feet. If I make the claim that my frame is equivalent to me being in a space ship traveling at g, doesn't that mean my whole body is accelerating at g uniformly? This is contrary to the previous statement though.