tmyklebu

9 ms·

31.
by tmyklebu 8y ago
> That’s why languages don’t represent dates as just as struct with ints In C, `struct tm` is literally a struct whose fields are all `int`s. But people typically represent time in C programs as an integer of some width measuring time i
32.
by tmyklebu 8y ago
> It is never "just an int". Soon you will ask questions about the int, and in a sufficiently large application you will forget the answers to the quesions easily, and scatter the same question (i.e., the same boolean logic) al
33.
by tmyklebu 9y ago
> I do not understand what the form of that matrix has to do with java or native heap. This seems to me as a completely orthogonal issue. As for the triangular form, this is supported in Neanderthal, as well as the rest of special struct
34.
by tmyklebu 9y ago
Aha, makes sense. (Now I see that at http://neanderthal.uncomplicate.org/articles/tutorial_native... ) Doesn't this make it very painful to do unusual operations on matrices? For example, solving linear systems
35.
by tmyklebu 9y ago
How do you use MKL and friends on objects in the Java heap? It seems like you'd have to copy to the native heap, do your linear algebra operation, and then copy the result back from the native heap.
36.
by tmyklebu 9y ago
It doesn't go lower than 0. Swapping can still hose your machine when swappiness is set to 0.
37.
by tmyklebu 9y ago
> If you sometimes run out of memory (or even get close), then you should have some swap. This seems fairly obvious to me. Relying on the OOM killer to "clean things up" is pretty dubious. But was there every any serious argume
38.
by tmyklebu 9y ago
> One problem with relying on the OOM killer in general is that the OOM killer is only invoked in moments of extreme starvation of memory. We really have no ability currently in Linux (or basically any operating system using overcommit)
39.
by tmyklebu 9y ago
> You're in for quite a surprise, particularly on desktop. I have a number of processes with some pages swapped out, and I see no impact on interacting with the said processes. Firefox, gDesklets, a volume changer, and several insta
40.
by tmyklebu 9y ago
Either way, I learned something. I can picture an array of 20 disks sustaining 2GB/s, but you aren't going to fit 20 disks into a laptop. I didn't realise a high-end SSD could get there, or even how much better regular SSDs
41.
by tmyklebu 9y ago
> Very few people on this thread read and understood the article. Hmm. I read the article and I think I understood it. However, in my experience, you run out of RAM if and only if your working set is too big. In my experience, all inv
42.
by tmyklebu 9y ago
> They could, but that's a lot like just making swap be manual. Sure. Isn't that a good thing? Rarely-used data can be swapped out to storage allocated for the purpose, as you desire, and too-large working sets don't hav
43.
by tmyklebu 9y ago
If I may ask, which disks are you using?
44.
by tmyklebu 9y ago
> The purpose of swap is not running things out of it. The purpose is shoveling unused data out of memory. And for that it doesn't need to be particularly fast. You can't detect a priori whether data is "unused." If
45.
by tmyklebu 9y ago
> I meant, in general settings (ie, no special problem structure), that you need full Hessians for Newton’s method. And, regarding conjugate gradient, in (non-DL) settings that I’m used to, that for good results you need preconditioners
46.
by tmyklebu 9y ago
> You mention Newton’s method, but of course that requires second order information which, as I mentioned, is not generally workable in high dimensions. Why would you say that second-order information is "not generally workable in h
47.
by tmyklebu 9y ago
> You can make an argument that, in high-dimensional parameter spaces, it’s hard to do better (because, gradient descent is linear in the number of dimensions). Nitpick: If you're interested in solving optimisation problems, it&#x2
48.
by tmyklebu 9y ago
Yep. (Largely) irrelevant in practice. But the gap between what we can do and what lower bounds we can prove is very large indeed for many matrix operations.
49.
by tmyklebu 9y ago
It looks like you also turned the rest of your post into a link. The best currently known exponent for square matrix multiplication is around 2.3728; Wikipedia's page on matrix multiplication has a reference.
50.
by tmyklebu 9y ago
The details people are talking about in that MathOverflow thread concern the precision needed to represent the numbers that crop up during Gaussian elimination. (They get huge, and if you are counting bit or word operations, then Gaussian
51.
by tmyklebu 9y ago
You can compute the inverse of a matrix A in asymptotically the same amount of time as you can multiply two matrices. You can also Cholesky factorise in that amount of time, and compute T^(-1) A where T is (upper or lower) triangular in th
52.
by tmyklebu 9y ago
> We compared our OSQP solver to other general-purpose solvers. That's why we chose GUROBI and Mosek. Your computational results don't support calling OSQP general-purpose. OSQP does okay on the easy problems you randomly gene
53.
by tmyklebu 9y ago
You could compare number of nodes explored rather than absolute timings to see how inaccuracy solving the relaxations affects branch-and-bound.
54.
by tmyklebu 9y ago
> Which version of OSQP did you try for? 0.2 has improved a lot compared to previous versions (much better convergence behavior with adaptive rho). I did a 'git clone' of your repository this morning; I have 0edd758. (I learne
55.
by tmyklebu 9y ago
Did you test miosqp against standard MIQPs? For example, in QPLIB, there is a handful of convex mixed-integer QPs.
56.
by tmyklebu 9y ago
What sort of QP problems are you hoping to solve using OSQP? When I tried OSQP on stock LP problems (i.e. the P = 0 special case; instances were afiro, adlittle, fit1p, dfl001, maros-r7, wood1p), I didn't get encouraging results. Apa
57.
by tmyklebu 9y ago
You're making a pretty big deal about trivial syntactic issues. > Into something that looks like > > auto *my_matrix = new MathArray<double, 10, 10>(); The dimensions here are a template parameter. They must be know
58.
by tmyklebu 9y ago
> 1) Most modern programming languages have ready-made implementations (by way of libraries) for almost every imaginable algorithm, I really don't think this is true of any programming language, modern or not. > written in the mo
59.
by tmyklebu 9y ago
> Major compilers (LLVM, GCC, Intel) are able to vectorize real world code to a useful extent. Try compiling this with recent gcc: uint8_t dumb_checksum(uint8_t *ar) { uint8_t ans = 0; for (int i = 0; i < 320; i++) a
60.
by tmyklebu 10y ago
Not sure I understand. Why should the number of home runs per year, the number of goals per year, and the number of touchdowns per year have equal variance?

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