How to GridFunctionCoefficient::Eval on a Different Mesh?

[j-signorelli]

Hi,

I am in the process of implementing a regression test for restarting simulations for code I wrote that relies heavily on MFEM. I have a ParGridFunction u_0 that I write out using VisitDataCollection, and then I import that outputted ParGridFunction into a new ParGridFunction u_r. To ensure that the functionality is working, I am trying essentially to do:

GridFunctionCoefficient u_0_coeff(u_0);
u_r->ComputeL2Error(u_0_coeff);

However, although the meshes associated with both ParGridFunction's are physically the same, they are different objects (pointing to different locations in memory). This leads to the following bug:

Verification failed: (GetLastOperation() == Mesh::REFINE) is false:
--> 
... in function: const mfem::CoarseFineTransformations& mfem::Mesh::GetRefinementTransforms()

as I traced this through: ParGridFunction::ComputeL2Error --> GridFunction::ComputeL2Error --> GridFunction::ComputeLpError --> GridFunctionCoefficient::Eval --> Mesh::GetRefinementTransforms.

In GridFunctionCoefficient::Eval, it seems to me that there is first a check to see if the meshes are pointing to the same location in memory, and if not, then it seems to presume that one mesh is a refined version of another?

Nonetheless: I believe that this error is occurring because u_r has no refinement done on it. Is this true? And if so, is there anyway that I can evaluate a GridFunctionCoefficient on a "different" (in memory) mesh?

Thank you for any assistance.

[vladotomov]

Hi @j-signorelli,

Does it work if you comment out this verification? I remember we've hit this in the past, and I think this check assumes that different meshes can only be used for LOR operations. @pazner can probably comment better.

[j-signorelli]

Hi @vladotomov

Thank you for your response. I ended up just using Vector::DistanceTo for each rank's ParGridFunction and just ensured that it is ~0 as a workaround.

However, I did just check this by commenting out the verification and unfortunately still got this error on every rank:

MFEM abort: Don't know how to construct CoarseFineTransformations for geom = 3
    ... in function: const mfem::CoarseFineTransformations& mfem::Mesh::GetRefinementTransforms()