Summary: Matrices.
Definition. Whenever m and n are positive integers we let
Mm
n = R{1,...,m}×{1,...,n}
and note that Mm
n is a vector space. If A Mm
n we frequently depict A as a rectangular array with m rows
and n columns:






A(1, 1) A(1, 2) · · · A(1, n)
A(2, 1) A(2, 2) · · · A(2, n)
...
...
...
...

Source: Allard, William K. - Department of Mathematics, Duke University

Collections: Mathematics