Column vector

From Wikipedia, the free encyclopedia

In linear algebra, a column vector is an m × 1 matrix, i.e. a matrix consisting of a single column of $\, m$ elements.

$\mathbf{x} = \begin{bmatrix} x_1 \\ x_2 \\ \vdots \\ x_m \end{bmatrix}$

The transpose of a column vector is a row vector and vice versa.

The set of all column vectors forms a vector space which is the dual space to the set of all row vectors.

[edit] Notation

To simplify writing column vectors in-line with other text, sometimes they are written as row vectors with the transpose operation applied to them.

$\mathbf{x} = \begin{bmatrix} x_1 \; x_2 \; \dots \; x_m \end{bmatrix}^{\rm T}$

$\mathbf{x} = \begin{bmatrix} x_1, x_2, \dots, x_m \end{bmatrix}^{\rm T}$

For further simplification, some authors also use the convention of writing both column vectors and row vectors as rows, but separating row vector elements with commas and column vector elements with semicolons (see alternative notation 2 in the table below). This alternative notation is used, for instance, in MATLAB, a widely used programming language specifically designed to simplify computations involving matrices.

	Row vector	Column vector
Standard matrix notation	$\begin{bmatrix} x_1 \; x_2 \; \dots \; x_m \end{bmatrix}$	$\begin{bmatrix} x_1 \\ x_2 \\ \vdots \\ x_m \end{bmatrix} \text{ or } \begin{bmatrix} x_1 \; x_2 \; \dots \; x_m \end{bmatrix}^{\rm T}$
Alternative notation 1	$\begin{bmatrix} x_1, x_2, \dots, x_m \end{bmatrix} \qquad$	$\begin{bmatrix} x_1, x_2, \dots, x_m \end{bmatrix}^{\rm T}$
Alternative notation 2	$\begin{bmatrix} x_1, x_2, \dots, x_m \end{bmatrix} \qquad$	$\begin{bmatrix} x_1; x_2; \dots; x_m \end{bmatrix}$