Re: help requested with extremely slow for loop?

[Joachim De Beule]

Many thanks to all of you, this is really interesting!

Are there any other 'insiders' I should know about with respect to sparse 
matrices? (I've read the 'Mathematical considerations' in the info file.) In 
particular, could you please expand on the following because I am not sure 
what it means.

> This should work well unless there are loop-carried dependencies
> assumed, in which case you'll need something more elaborate. 


> If you have thousands of independent vectors, you may also consider
> stacking them in a matrix.

So you mean sth like xs = [x1 x2 ... x3], with the xi one of the x's in the 
previous code? Actually that is what I have, but I am not sure what that gives 
me with respect to the calculations, I still need a for loop:

for i = 1:length(xs)
        idxs = find(xs(:,i) & y);
        xs(:,idxs(i)) += xs(:,i);
        xs(:,i) = 0;
endfor

Or am I missing something again?

Joachim