[ublas] Questions about indexing and tensor contractions

Subject: [ublas] Questions about indexing and tensor contractions
From: Thomas Yang (ThomasYang_at_[hidden])
Date: 2019-03-29 21:56:53

Hello,

Recently, I came across the index utility "number_equal_indices<>" method,
which is used in the implementation of tensor contraction. If my
understanding is correct, this appears to facilitate the implementation of
Einstein summations, where common indices between two tensors/matrices are
summed.

My question now is - what happens when there are more than one equal index
(i.e. both tensors use indices i and j)?

Thanks,

Thomas Yang