public static double SolveLeastSquares(Mat3 a, Vector3 b, out Vector3 x, double svd_tol, int svd_sweeps, double pinv_tol)
{
var at = MatUtils.Transpose(a);
var ata = MatUtils.MmulAta(a);
var atb = MatUtils.VMul(at, b);
return(SolveSymmetric(ata, atb, out x, svd_tol, svd_sweeps, pinv_tol));
}