[Tutor] matrix-vector multiplication errors

[Dinesh B Vadhia]

I've posted this on the Scipy forum but maybe there are answers on Tutor too.  I'm performing a standard Scipy matrix* vector multiplication, b=Ax , (but not using the sparse module) with different sizes of A as follows:  


Assuming 8 bytes per float, then:
1. matrix A with M=10,000 and N=15,000 is of approximate size: 1.2Gb
2. matrix A with M=10,000 and N=5,000 is of approximate size: 390Mb
3. matrix A with M=10,000 and N=1,000 is of approximate size: 78Mb

The Python/Scipy matrix initialization statements are:
> A = scipy.asmatrix(scipy.empty((I,J), dtype=int))
> x = scipy.asmatrix(scipy.empty((J,1), dtype=float))
> b = scipy.asmatrix(scipy.empty((I,1), dtype=float))

I'm using a Windows XP SP2 PC with 2Gb RAM.

Both matrices 1. and 2. fail with INDeterminate values in b.  Matrix 3. works perfectly.  As I have 2Gb of RAM why are matrices 1. and 2. failing?

The odd thing is that Python doesn't return any error messages with 1. and 2. but we know the results are garbage (literally!)

Cheers!

Dinesh
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