I did not check the link ... but Don't use define property to return the height. Just define it as static double ... #include "udf.h"n´╗┐nstatic double the_height(double t, double x){nn CALCULATE y HERE .....return y;n}nnDEFINE_GRID_MOTION(.....)n{nn When you need y ...nny = the_height( t, x);nn USE ynn}n

Okay, so then CALCULATE y HERE is just the function for interpolating the data.n