[Numpy-discussion] matrix multiplication A x, x has some zeros

Alan G Isaac aisaac@american....
Fri Dec 14 07:28:47 CST 2007


On Fri, 14 Dec 2007, dmitrey apparently wrote:
> I guess it doesn't matter, but typical n are 1...1000. 
> However, I need to call the operation hundreds or thousands times (while 
> running NLP solver ralg, so 4..5 * nIter times). 
> Number of zeros can be 0...n-1 

Do both A and x change every iteration?

Anyway, if x is sparse I think you'll get some
benefit by doing
idx=N.ravel(x)!=0
A[:,idx]*x[idx]

hth,
Alan Isaac






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