invert expression function

Inverts a matrix.

This is only valid if the matrix is a 4×4 or 3×3 matrix. If the matrix is larger than 4×4, the matrix will be converted to a 4×4 matrix before it is inverted. If the matrix is smaller than 3×3, the matrix will be enlarged to a 3×3 matrix before it is inverted. The results of enlarging the matrix to a 3×3 are not guaranteed.