[Numpy-discussion] expensive tensordot

Paul Northug pnorthug@gmail....
Tue Jun 15 13:15:58 CDT 2010

I have a computation bounded by one step and I have always wondered
how to make it fast enough to be useable. I suspect that I have to use
an approximation, but I was hoping someone would spot a major
inefficiency in my implementation.

The calculation is a kind of outer product of two sets of time series:

for n,p in np.ndindex(self.P, self.P):
     self.A[:,n,:,p] += np.tensordot(a[:,:,n:n+self.T],
([0,2], [0,2]))

The sizes for all indices are on the order of 100 with the exception
that a.size[0] == 10. One inefficiency is that A is symmetric in (n,p)
but this is only a factor of 2.


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