determinant method
get the determinate of the matrix
Implementation
double determinant() {
List<double> te = elements;
double a = te[ 0 ], b = te[ 1 ], c = te[ 2 ],
d = te[ 3 ], e = te[ 4 ], f = te[ 5 ],
g = te[ 6 ], h = te[ 7 ], i = te[ 8 ];
return a * e * i - a * f * h - b * d * i + b * f * g + c * d * h - c * e * g;
}