Matrix multiplication
Notation

This article will use the following notational conventions: matrices are represented by capital letters in bold, e.g. A; vectors in lowercase bold, e.g. a; and entries of vectors and matrices are italic (they are numbers from a field), e.g. A and a. Index notation is often the clearest way to express definitions, and is used as standard in the literature. The entry in row i, column j of matrix A is indicated by (A), A or a. In contrast, a single subscript, e.g. A, A, is used to select a matrix (not a matrix entry) from a collection of matrices.
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