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Subject: Re: [ublas] Element-wise operations are really slow
From: xiss burg (xissburg_at_[hidden])
Date: 2010-04-21 21:55:00


I tried the mapped_matrix, and it performed as bad as compressed_matrix. I
can't understand why because everyone says it is faster and I could see it
myself in a simple app I wrote, like that sparse fill samples. I can't
understand what is wrong with my code. Guys recommended me to use a
generalized_vector_of_vector to build the global stiffness matrix and then
copy it to the compressed_matrix (which is a good choice for multiplications
later), then I got something like this

Just to explain that code better, t->getGlobalIndex(j) and t->
getCorotatedStiffness0(j, k) are just regular gets, nothing special happens
inside them. t->computeCorotatedStiffness() is not something computationally
expensive, it performs one Gram-Schimdt orthonormalization on a 3x3 matrix
and then 32 3x3 matrix multiplies (not using ublas matrices there). No
matter what matrix I use for RKR_1 and RK I get the same poor performance.
One proof that makes the code slow is that if I comment those two lines
where I perform the element wise sum, one of my samples runs 15-20 times
faster (in this specific sample, m_tetrahedrons.size()==617). Then, I'm
really lost there, I wouldn't like to just throw all my work with ublas away
because of this. There must be a solution to this problem.


Hey that eigen looks awesome, very promising. If I don't get to solve this
problem with ublas soon, I may give it a try. Thanks for the suggestion.

Thanks guys,