/// <summary>
/// Helper function: applies the matrix L to the vectors px, py and pz separately and returns the resutls.
/// Can compute the differential (=Laplacian) coordinates of the mesh as 3 arrays
/// </summary>
public static void ComputeDifferentialCoordinates(SparseMatrix L, double[] px, double[] py, double[] pz,
out double[] dx, out double[] dy, out double[] dz)
{
/// multiply dx = L*px
L.Ax(px, out dx);
L.Ax(py, out dy);
L.Ax(pz, out dz);
}