Multiplication of integrals is unsupported

[dokken]

@josue707

(u*ds(1))*(v*ds(1))) +

This is an incredibly dense matrix. Are you sure you want this in your variational form?

I would compute
a=dolfinx.fem.petsc.assemble_vector(dolfinx.fem.form(u*ds(1)))
b=dolfinx.fem.petsc.assemble_vector(dolfinx.fem.form(v*ds(1)))

Then find the nonzero entries of these two vectors, (hopefully there are many).

One can then in turn add these to an assembled matrix A with setvalueslocal as for instance shown in:

PETSc matrices and vectors I/O

Consider the following: from petsc4py import PETSc from mpi4py import MPI A = PETSc.Mat().create(MPI.COMM_WORLD) A.setSizes([3, 3]) A.setFromOptions() A.setUp() A.setValuesLocal([0], [2], [3]) A.assemble() viewer = PETSc.Viewer().createBinary("A.mat", mode=PETSc.Viewer.Mode.WRITE, comm=MPI.COMM_WORLD) viewer(A)