If I want to calculate the coupled stiffness matrix K_uT or K_Tu for a two-field coupled problem?

[zyhsjtu]

For a two-field problem,i.e., thermo-elastic problem. If I want to calculate the global coupling matrices K_uT or K_Tu, is there a way to achieve this efficiently? If I define Kud as K_ud=spzeros(nudofs,nTdofs) and then asssemble it using my eledofs, it seems slow.

[KnutAM]

You could probably use the sp = BlockSparsityPattern (although the documentation is a bit scarce at the moment) in combination with renumber!:ing FieldWise. If you don't add nonzero values to the non-coupling matrices the overhead of having these should be negligible I think. For the assembly, then you should use the standard assembler obtained from start_assemble(K, [f]), where K = allocate_matrix(sp).

I haven't tried this functionality myself yet though.

[fredrikekre]

#1050 has some examples

[zyhsjtu]

Thanks for your suggestion, I will see this #1050