lderror = ref.lowerDiagonal();
lderror.subAssign(op2.lowerDiagonal());
derror = ref.diagonal();
derror.subAssign(op2.diagonal());
uderror = ref.upperDiagonal();
uderror.subAssign(op2.upperDiagonal());
for (i=2; i<grid.size()-2; i++) {
if (Math.abs(lderror.get(i)) > tolerance ||
Math.abs(derror.get(i)) > tolerance ||