- `TF = ismatrix (X)`

Return `true` if `X` is a 2-D array.

A matrix is an object with two dimensions (`ndims (X) == 2`) for which
`size (X)` returns `%[M, N]%` with non-negative `%M%` and `%N%`.

See also: `isscalar`, `isvector`, `iscell`, `isstruct`, `issparse`, `isa`.

### References

- https://www.mathworks.com/help/matlab/ref/ismatrix.html
- https://octave.sourceforge.io/octave/function/ismatrix.html