CODEWITHSUNDEEP
pythonnumpy
Rodriguez
Rodriguez

Reputation: 259

What is the difference between tensordot and einsum in numpy?

For my understanding, tensordot http://docs.scipy.org/doc/numpy-1.10.1/reference/generated/numpy.tensordot.html is multiply two tensors and sum given indices. This is precisely einsum does.

Actually what is the difference between this two functions? Is that due to different performance?

Upvotes: 3

Views: 1408

Answers (1)

hpaulj
hpaulj

Reputation: 231385

They are different approaches to similar problems. einsum is more general. Speed can be similar, though you need to check individual cases.

tensordot works by reshaping and transposing axes, reducing the problem to one that np.dot can solve. Its code, up to the dot call is Python, so you can read it for yourself.

einsum is built 'from-ground-up' to work with the 'Einstein notation' that is used in physics (it was written by scientist for fit his needs and usage). The documentation covers that. It is C code, so is a little harder to study. Basically it parses the indexing string, and builds an nditer object that will iterate over the input arrays, performing some sort of sum-of-products calculation. It can take short cuts in case where you just want indexing, diagonal, etc.

There have been number of questions asking about either of these functions, or suggesting their use in the answers.

In new versions there is also a np.matmul that generalized dot in a different way. It is linked to the new @ operator in Python3.5.

Upvotes: 8

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