##

Special matrices

Besides by direct input, some special matrices can also be formed directly with MATLAB commands. These matrices are:
- An
zero matrix, i.e., a matrix in which all elements have the value zero, is formed with the command
`zeros(m,n)`

.
- An
matrix whose elements all equal one is formed with the command
`ones(m,n)`

.
- An
matrix with random numbers, uniformly distributed between 0 and 1, is formed with the command
`rand(m,n)`

.
- An
diagonal matrix, i.e., a matrix in which only the diagonal elements (the elements with equal row and column indices) have a non-zero value, is formed with the command
`diag(v)`

, where
is a vector containing the
diagonal elements.
- An
unit matrix, i.e., a diagonal matrix for which all diagonal elements equal one, is formed with the command
`eye(n)`

.

If you want to give a matrix the same size as a given matrix
, then you can do this by using the command `size`

. For example, the command

`>> zeros(size(A))`

forms a zero matrix with the same size as the matrix
. Of the above commands, only the command `diag`

accepts a matrix as its argument. The result of the command `diag(A)`

, where
is a matrix, is a column vector consisting of the diagonal elements of
.

Esteur
2010-03-22