[firedrake] Multi-grid preconditioning

[Lawrence Mitchell]

> On 29 Jul 2015, at 17:26, Justin Chang <jychang48 at gmail.com> wrote:
> 
> Is there support for Multi-grid preconditioning? I think I saw somewhere where this was not supported yet. Because applying -pc_type gamg for my mixed forms returns me errors.

If you want to apply AMG to your mixed form, you'll need to assemble a monolithic matrix. Pass nest=False when either assembling the operator or building your solver. 

However, this may not work well, you might want to do gamg on one of the blocks, using fieldsplit preconditioners: all the normal PETSc options work. 

Lawrence