public function isNonsingular()
    {
        for ($j = 0; $j < $this->n; $j++) {
            if ($this->LU[$j][$j] == 0) {
                return false;
            }
        }
        return true;
    }
public function isNonsingular()
    {
        for ($j = 0; $j < $this->n; $j++) {
            if ($this->LU[$j][$j] == 0) {
                return false;
            }
        }
        return true;
    }
public function isNonsingular ( ) { for ( $ j = 0 ; $ j < $ this -> n ; $ j ++ ) { if ( $ this -> LU [ $ j ] [ $ j ] == 0 ) { return false ; } } return true ; }
Is the matrix nonsingular?
@return true if U, and hence A, is nonsingular.
Is the matrix nonsingular?