[Numpy-discussion] Help with the tensordot function?
Fri Sep 3 06:02:47 CDT 2010
Can someone help me replace a slow expression with a faster one based on
tensordot? I've read the documentation and I'm still confused.
I have two matrices b and d. b is n x m and d is m x m. I want to replace
>>> bdb = zeros(n,'d')
>>> for i in xrange(n):
>>> bdb[i,:] = dot(b[i,:],dot(d,b[i,:])
with something that doesn't have the for loop and thus is a bit faster.
The first step is
>>> bd = dot(b,d)
However, following this with
>>> bdb = dot(bd,b.T)
doesn't work, since it yields a n x n matrix instead of an n x 1 vector.
Reading the notes on tensordot makes me think it's the function to use, but
I'm having trouble grokking the axes argument. Can anyone help?
Thanks in advance!
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