constrain spherical harmonics coefficients

haoliu

Hello,

I am using spherical harmonics to account for a hkl-dependent peak asymmetry (like the one in clay.inp) in my pattern. Since the hkl dependence is known qualitatively(eg. h00 and 0k0 skewed towards lower 2th, and 00l skewed towards higher 2th), I would apply constraints to the generated spherical harmonics coefficients. I have worked out the mathematical relationship between different coefficients, for example

sh_c00 + sh_c20 + sh_c40<0

in order to implement this, I did something like this

y00 sh_c00 4.59108`_1.94561 max=-sh_c20-sh_c40;

This works fine when I have two or three constraints, but when I tried to include more, the refinement didn't seem to do anything, and I guess this is because all the refined parameters are inter-constrained and their values couldn't change much. Does anyone know any clever way around this?

Thanks,
Hao

johnsoevans

You could try restraints rather than constraints and e.g. using "If" statements on restraint calculations. Not sure if it would be a good idea in practice though!