How to work around lack of dynamic profiles in porting from Epetra to Tpetra?

[jjramsey]

As I mentioned in an earlier question, I've started an attempt to port an old code from Epetra to Tpetra, since Epetra is being deprecated.

There are a couple uses of Epetra in the old code. In one, I'm doing the usual routing of assembling a global matrix for a linear finite element calculation: looping over elements "owned" by a processing element and summing their stiffness matrices into the global matrix. I do this in two steps, first assembling an Epetra_FECrsGraph by looping over the elements almost as if I were assembling the matrix proper (except not calculating the stiffness matrices), and second by constructing an Epetra_FECrsMatrix from the graph and then looping over the elements again and summing their stiffness matrices into this matrix. (I think this was done in an example code from Didasko.)

The other use was to generate an adjacency list from a list of elements and the nodes that belonged to each of them. Again, I was looping over elements "owned" by a processing element, and the process went much like the aforementioned assembly of the graph.

In both of these uses, I relied on Epetra_FECrsGraph having a dynamic profile. It was unclear to me how many nonzeros per row I needed, so I let the process of finite element assembly do it for me. Now, with the constructors of Tpetra's CrsGraph and FECrsGraph all requiring upfront knowledge of the number of nonzeros (or something that entails that knowledge), the lack of a dynamic profile in Tpetra presents a problem.

Are there known workarounds for this issue, or some sane straightforward way of finding the number of nonzeros that I hadn't thought of?

Tagging @trilinos/tpetra

[cgcgcg]

@trilinos/tpetra

[cgcgcg]

We had two talks at the Trilinos User Group meeting two years ago that might be helpful:

• Epetra to Tpetra Transition in ALEGRA
• Using Kokkos In Tpetra Finite Element Assembly

There also is an example in Tpetra: https://github.com/trilinos/Trilinos/tree/develop/packages/tpetra/core/example/Finite-Element-Assembly

[jjramsey]

I looked at those, and they all had the same problem: glossing over how to obtain the number of nonzeros.

In Epetra to Tpetra Transition in ALEGRA and https://github.com/trilinos/Trilinos/tree/develop/packages/tpetra/core/example/Finite-Element-Assembly, the number of nonzeros was just a given: MAX_NODE_ENTRIES_PER_ROW in the slides, and 16 on line 133 of fem_assembly_InsertGlobalIndices_FE.hpp .

In Using Kokkos In Tpetra Finite Element Assembly, nothing was said about the maximum number of nonzeros at all. The allocation of fe_matrix, whatever it was, was taken for granted.

[cgcgcg]

@csiefer2

[csiefer2]

@cgcgcg linked to the example of how to use the Tpetra::FECrsMatrix above. Checking that out might help.

[jjramsey]

@cgcgcg linked to the example of how to use the Tpetra::FECrsMatrix above. Checking that out might help.

That example still assumes a specific number of nonzeros per row.