public virtual Vector[] Calculate_ElementNodal_DUDX() { double[] Ue = Get_ElementNodal_U(); Vector[] Xi = Interpolator.Calculate_ElementNodal_Xi(); int NNPE = Xi.Length; Vector[] DUDX = new Vector[NNPE]; for (int i = 0; i < NNPE; i++) { DUDX[i] = Interpolator.Interpolate_DerivativeOfVariable_WRTX(Xi[i], Ue, ElementNodes); } return(DUDX); }