Editing Matrix multiplication (section)

==Notation==
This article will use the following notational conventions: matrices are represented by capital letters in bold, e.g. {{math|'''A'''}}; [[Euclidean vector|vectors]] in lowercase bold, e.g. {{math|'''a'''}}; and entries of vectors and matrices are italic (they are numbers from a field), e.g. {{math|''A''}} and {{math|''a''}}. [[Index notation]] is often the clearest way to express definitions, and is used as standard in the literature. The entry in row {{mvar|i}}, column {{mvar|j}} of matrix {{math|'''A'''}} is indicated by {{math|('''A''')<sub>''ij''</sub>}}, {{math|''A''<sub>''ij''</sub>}} or {{math|''a''<sub>''ij''</sub>}}. In contrast, a single subscript, e.g. {{math|'''A'''<sub>1</sub>, '''A'''<sub>2</sub>}}, is used to select a matrix (not a matrix entry) from a collection of matrices.