3 m : matrix([1,2],[1,2]);
9 ptriangularize(m-z*ident(2),z);
11 m : matrix([1,2,3],[4,5,6],[7,8,9]) - z * ident(3);
13 mm : ptriangularize(m,z);
23 m : matrix([1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,16]);
27 apply('orthogonal_complement, args(nullspace(transpose(m))));