The number of rows == the number of columns

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.