[CIG-MC] coupler & multigrid solver?

[Magali Billen]

Hello,

I've been doing some test models using the coupler option, embedding a  
higher resolution
regional mesh into  a larger low resolution regional mesh.

I had the unpleasant surprise of finding this error message when I  
tried to use the multigrid solver:
...
AssertionError: Error: solver.vsolver.Solver must be "cgrad"

Knowing how slow conjugate gradient is compared to multigrid for most  
problems, this is a huge
disappointment - in particular because, as far as I can tell, its not  
mentioned anywhere in the manual.

So, I'm wondering why doesn't the coupler work with multigrid? Is this  
something that should work,
but hasn't been tested, or is there something about how the  
information gets past between the
coupled models that prevents the use of the multigrid solver?

Given how slow conjugate gradient is, it seems that any benefit from  
using less nodes by embedding meshes will be completely lost  by  
having to use the conjugate gradient solver instead of multigrid.

Magali