How can I define an anisotropic conductivity?

demigod

How can I define an anisotropic thermal conductivity as following:

thermcal conductivity for x direction is constant, for example, kx = 3; and thermal conductivity for the y direction is varied with y, for example, ky = y^2.

I write an udf to define the position-related thermal conductivity. as following,

DEFINE_PROPERTY(udf_material, c, t) { real z_thermal_conductivity;

real xc[ND_ND];

C_CENTROID(xc,c,t);

z_thermal_conductivity = xc[1]*xc[1];

return z_thermal_conductivity; }

and hook this udf in the orthotropic setting.

But it will give a error like following,

Error: GENERAL-CAR-CDR: invalid argument [1]: improper list Error Object: #f

and the result is wrong.

How can i do? Thanks.