Compute the inverse of the square matrix a. Return an estimate of the reciprocal condition number if requested, otherwise warn of an ill-conditioned matrix if the reciprocal condition number is small.
If called with a sparse matrix, then in general x will be a full matrix, and so if possible forming the inverse of a sparse matrix should be avoided. It is significantly more accurate and faster to do y
=a\b, rather than y= inv (a) *b.