Unable to install bcrypt-ruby 3.1.1
Rails: Could not find bcrypt-ruby-3.0.1 in any of the sources
R's lmer cheat sheet There's a lot of discussion going on on this forum about the proper way to specify various hierarchical models using lmer.  I thought it would be great to have all the information in one place. A couple of questions to start:   How to specify multiple levels, where one group is nested within the other: is it (1|group1:group2) or (1+group1|group2)? What's the difference between (~1 + ....) and (1 | ...) and (0 | ...) etc.? How to specify group-level interactions? Where did dedicated.abac.net. come from in my rDNS and PTR records? How do I find out which dlls an executable will load? If I have a Windows executable, how can I find out which dlls it will load?  I'm just talking about which ones that will be loaded statically, not ones it might load dynamically with something like LoadLibrary. Proving that the function is differentiable and $f'(0)=0$ Consider a function $f (x) $ such that $f (x)=\begin {cases} x^2 &amp;  \text {x=irrational}     \\ 0   &amp;\text {x=rational} \end {cases}$ Then prove that $f $ is differentiable  at $x=0$ and $f'(0)=0$ $$\text {Attempt} $$ .                  .  Now I consider two sequences $x_n=\frac {\sqrt{2}}{n},y_n=\frac {1}{n} $ one irrational one rational both going to $0$ as $n\to \infty $. But now the problem is how to consider LHD,RHD.Do we have to consider irrational case then rational case and if both limits go to same value then say that function is differentiable.I can easily see the graph on graphical calculator and verify the result but I am more interested in analytical method. What is known about $\mathcal C^\infty$ functions $\mathbb R\to\mathbb R$ that always take rationals to rationals? Are they all quotients of polynomials? If not, are there any that are bounded yet don't tend to a limit for $x\to +\infty$? If there are, then can we also require them to be analytic?  (This is basically just a random musing after I found myself using trigonometric functions twice in unrelated throwaway counterexamples. It struck me that it was kind of conceptual overkill to whip out a transcendental function for the purpose I needed: basically that it had to keep wiggling forever. I couldn't think of a nice non-trancendental function to do this job, however, and now wonder whether that is because they can't exist). How do you use Batch for send more than 10 emails? Does there exist a laser that is tunable over the whole visible spectrum? Does there exist a laser that is tunable over the whole visible spectrum? If so does there exist one that is solid state? This is to settle a score with my dumb workmates. Evolution of the Redundancy of the Genetic Code How to find the reduced density matrix of a four-qubit system? I have the state vector $|p\rangle$ made up of 4 qubits. Say system A is made up of the first and second qubits while system B is made up of qubits 3 and 4. I want to find the reduced density matrix of system A.   I know I could separately extract qubits 1,2 and 3,4 into their own state vectors then find their density matrices and compute the reduced density matrix for system A.  I want to figure out how to do this without having to extract and separate the systems. First I would find the density matrix of $|p\rangle$ and then do a partial trace with respect to system B. I am not sure how to do the partial trace of system B since the system contains 2 qubits.  Can anyone help me figure this out? I am using Python and NumPy for reference. Web designer's link back to own website (rel="designer" / rel="nofollow") Functional Equation (no. of solutions): $f(x+y) + f(x-y) = 2f(x) + 2f(y)$ Find all the functions $f\colon\mathbb{Q} \to \mathbb{Q}$ such that $f(x+y) + f(x-y) = 2f(x) + 2f(y)$, for all rationals $x,y$. How can I install Minecraft? I have tried many tutorials but none of them are clear enough. I have also tried installing it using Wine but it won't update and Wine goes gray and stops working.  Does anybody know an easy way to install Minecraft though the Java file without using Wine? Can prematurely powering down a computer cause bad sectors in a hard drive? Q1: Can forcibly powering off a PC without using the built-in shutdown/reboot functions, cause a HDD to accumulate bad sectors? Whether it be the result of BSODs, lockups, crashes, etc.   Q2: If so, are these bad sectors repairable? I know an OS typically relocate bad sectors to other areas of the drive, but once a drive accumulates too many it just dies.   I have read up and saw things about 'soft' and 'hard' bad sectors. One caused by software and the other being actual physical damage. The reason I am asking this is because I have had several HDDs die on me in the past year, far before their estimated lifespan, and one thing they all had in common was that I had forcibly powered off my PC a lot. I have two partitions, one of them has a file system and the other is unallocated.  How to merge two partitions? How to write an RSS feed with Java? I'm using Java, and need to generate a simple, standards-compliant RSS feed. How can I go about this? Call to getLayoutInflater() in places not in activity How to programmatically login/authenticate a user? Is there any way to kill a Thread? Can you deliver it [when,after] it [is | will be] assembled? Bootstrap Paradox in Interstellar