The eye function returns a dense identity matrix with specified dimensions.

The speye function returns a sparse identity matrix with specified dimensions.

If n is an integer and m is omitted, the resulting matrix is square.

If the input X is an array, its elements are used as the dimensions of the matrix.

$\mathrm{with}\left(\mathrm{MTM}\right)\:$

$\mathrm{eye}\left(4\right)$

$\left[\begin{array}{cccc}1& 0& 0& 0\\ 0& 1& 0& 0\\ 0& 0& 1& 0\\ 0& 0& 0& 1\end{array}\right]$

$\mathrm{eye}\left(4\,5\right)$

$\left[\begin{array}{ccccc}1& 0& 0& 0& 0\\ 0& 1& 0& 0& 0\\ 0& 0& 1& 0& 0\\ 0& 0& 0& 1& 0\end{array}\right]$

$\mathrm{speye}\left(4\right)$

$\left[\begin{array}{cccc}1& 0& 0& 0\\ 0& 1& 0& 0\\ 0& 0& 1& 0\\ 0& 0& 0& 1\end{array}\right]$

$\mathrm{speye}\left(4\,5\right)$

$\left[\begin{array}{ccccc}1& 0& 0& 0& 0\\ 0& 1& 0& 0& 0\\ 0& 0& 1& 0& 0\\ 0& 0& 0& 1& 0\end{array}\right]$