Tensor contraction - Wikipedia
https://en.wikipedia.org/wiki/Tensor_contractionIn multilinear algebra, a tensor contraction is an operation on a tensor that arises from the natural pairing of a finite-dimensional vector space and its dual. In components, it is expressed as a sum of products of scalar components of the tensor(s) caused by applying the summation convention to a pair of dummy indices that are bound to each other in an expression. The contraction of a single mixed tensoroccurs when a pair of literal indices (one a subscript, the other a superscript) of th…
Tensor - Wikipedia
https://en.wikipedia.org/wiki/TensorIn mathematics, a tensor is an algebraic object that describes a multilinear relationship between sets of algebraic objects related to a vector space. Objects that tensors may map between include vectors and scalars, and even other tensors. There are many types of tensors, including scalars and vectors (which are the simplest tensors), dual vectors, multilinearmaps between vector spaces…