jedbrown

78 ms·

721.
by jedbrown 17y ago
You are probably familiar with this page http://www.fceia.unr.edu.ar/~fisicomp/apuntes/biblios/wnotnr... and the suggested alternatives http://www.fceia.unr.edu.ar/~fisicomp/apuntes/biblios/altnr.... In addition to those suggestions, he
722.
by jedbrown 17y ago
If you are using CG on a matrix that isn't SPD, then you are doing something very wrong. Actually, this isn't so weird. There are a number of domain decomposition schemes that use CG, but keep all iterates in a benign space on which the op
723.
by jedbrown 17y ago
With CG, the preconditioner also needs to be SPD (or have suitable factors). You can get by pretty well using only GMRES and spend all your time thinking about preconditioners. Once you have some good candidate preconditioners, you can tr
724.
by jedbrown 17y ago
Matlab's backslash is the GPL'd Umfpack (relicensed from the author). The most important thing to know about iterative solvers is that the Krylov method is a minor component, preconditioning is the hard part.
725.
by jedbrown 17y ago
The asymptotics are completely different for sparse and banded matrices. And NR really isn't a good reference unless you are looking for a mildly flawed 30 year old analysis.
726.
by jedbrown 17y ago
Except that the normal equations are rarely a good way to compute the action of the pseudoinverse (though explicitly computing it would be even worse). QR is the workhorse for under- and over-determined dense systems, with SVD as a fallbac
727.
by jedbrown 17y ago
It's in the frame pointer. Edit: You're right, optimized code might not save the frame pointer and this wouldn't provide any benefit if your frame had unknown size. But usually the preamble saves the old ESP in EBP and it is restored at th
728.
by jedbrown 17y ago
Actually, come to think of it, when the function doesn't call anything else, locals will be indexed off the base pointer and the stack pointer will not be explicitly moved. So it costs two extra instructions to get aligned locals in a func
729.
by jedbrown 17y ago
Aligning the stack at runtime is one instruction in the preamble so it's not a big deal, especially if the function is big enough to have non-register SSE locals. Also, when using VLAs, it's not optional. I use SSE all the time and have n
730.
by jedbrown 17y ago
Most compilers produce exclusively SSE instructions for floating point these days (unless you're explicitly generating code for machines that don't support it). But the stack doesn't need to be aligned at the call site for this, it can be
731.
by jedbrown 17y ago
Making internals transparent is a very bad thing when it encourages users to write code that relies on implementation details. On the other hand, a certain amount of transparency is critical so that users can easily develop a mental perfor
732.
by jedbrown 17y ago
My experience on x64 has been that Sun is usually competitive with GCC/ICC, but not clearly better. Sun's C99 compiler does really atrocious things with SSE intrinsics, strange since their C++ compiler handles intrinsics almost as well as
733.
by jedbrown 18y ago
Then you would have to change the measure to get both curves to integrate to 1. Of course the distribution is nonsense to begin with.
734.
by jedbrown 18y ago
A (truncated or folded) normal distribution is completely inappropriate here.