Elise Palethorpe

> @elise-palethorpe also perhaps change the validation script name as @glwagner suggest? Do we need the file at all? Can I just include mg preconditioner in `doubly_bounded_poisson.jl`

> Shoudn't we write a kernel? Presumably that explicit 3D loop is incredibly slow? Indeed! Unfortunately it's not embarrassingly parallel so my kernel skills are no longer sophisticated enough :)...

It appears that the Poisson equation is hard coded to be the linear operator https://github.com/weymouth/GeometricMultigrid.jl/blob/4e09502c86a0da1941544a784bc709acb8737052/src/MultiGrid.jl#L44 Is this for simplicity? Could we instead use the restriction and interpolation matrix technique detailed...