A good answer might be:

The number of rows == the number of columns

Square Matrix

In a square matrix the number of rows equals the number of columns. In computer graphics, square matrices are used for transformations.

A column matrix consists of a single column. It is a N x 1 matrix. These notes, and most computer graphics texts, use column matrices to represent geometrical vectors. At left is a 4 x 1 column matrix. A row matrix consists of a single row. (Some books use row matrices to represent geometical vectors).

Some books call a column matrix a column vector and call a row matrix a row vector. This is OK, but can be ambiguous. In these notes the word vector will be used for a geometric object (a directed line segment). In these notes, column matrices will be used to represent vectors and will also be used to represent geometric points.


What are square matrices used for?