private double[] NormalVector(double[,] m, List <double[]> dRho)
{
double detm = MetricTensorDet(m);
double[] drhoBydrho = VectorOperations.VectorCrossProduct(dRho[0], dRho[1]);
double[] n = VectorOperations.VectorScalarProductNew(drhoBydrho, 1.0 / (Math.Sqrt(detm)));
return(n);
}