Matrix multiplication in numpy

Question

I have 2 boolean matrices in numpy and am using the .dot() function to multiply them and the results I get is a boolean matrix.

Is there a way to the get the sum of the product of the respective elements during the multiplication that I would get if I was doing matrix multiplication and the elements were either 1 or 0?

i.e. the elements in the resulting matrix should either be 0 or non-zero integers.

Thanks in advance.

alko · Accepted Answer · 2013-12-04 11:19:36Z

2

Convert to int with astype.

Demo:

>>> import numpy as np
>>> np.random.seed(5)
>>> a = np.random.random([3,3]) > 0.5
>>> b = np.random.random([3,3]) > 0.5

Now a, b are arrays of dtype bool:

>>> a
array([[False,  True, False],
       [ True, False,  True],
       [ True,  True, False]], dtype=bool)

Multiply them as integers:

>>> np.dot(a.astype(np.int), b.astype(np.int))
array([[0, 0, 1],
       [0, 0, 1],
       [0, 0, 2]])

answered Dec 4, 2013 at 11:19

alko

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