Re: [ESPResSo-devel] LB fluid with variable viscosity

[Michael Kuron]

Hi Ivan,

> But according to this value I will be able to assign proper shear,
> bulk, ghost even, ghost odd relaxation times. So only one real number
> for each lbnode will be necessary to store.

If you update this field less often than once per timestep, it might
make sense to store all relaxation times instead of the single number
as that will save you some computation time (including divisions, which
are rather expensive on GPUs).

> But I am not sure how to implement such a field. Could you please
> point me out to some similar variable in ESPResSo, co I can implement
> it in a similar manner?

I guess it would be similar to the LB force field (node_f in
lbgpu_cuda.cu or lbfields[index].force_density in lb.cpp).

> Or is there a guide how to implement a global field so that
> parallelization will be taken care of?

You don't need to worry about parallelization. You can calculate this
field locally on each MPI rank because it only depends on particles
that are on that MPI rank. Furthermore, on the GPU you don't need to do
anything because the particles from all MPI ranks are present on the
GPU.

Michael