Null space of matrix

`null(A)`

calculates the singular value decomposition of the matrix,
`[U,S,V] = svd(A,0)`

. The columns of `V`

that do not
correspond to nonzero singular values form a set of orthonormal basis vectors for the null
space.

The "rational" basis for the null space `null(A,'r')`

is obtained from
the reduced row echelon form of `A`

, as calculated by
`rref`

.