[Numpy-discussion] numarray bug: dot product between 2x2 and 3x2x3 on Mac different from PC

Travis Oliphant oliphant.travis at ieee.org
Tue Jul 18 03:46:30 CDT 2006


Sebastian Haase wrote:
> On Monday 17 July 2006 12:38, Travis Oliphant wrote:
>   
> Any idea on my main question ?
> What is the dot product of a 2x2 and 3x2x3 supposed to look like ?
> Why are numarray and numpy giving different answers ??
>   

I'm pretty sure the dot-product in Numeric (and I guess numarray too) 
was broken for larger than 2-dimensions.  This was fixed several months 
ago in NumPy.

NumPy dot-product gives the following result

a.shape is (I,L)
b.shape is (J,L,K)

Then c=dot(a,b) will have c.shape = (I,J,K) with

c[i,j,k] = sum(a[i,:]*b[j,:,k])


I'm not even sure what Numeric is computing in this case.

-Travis






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