p-multigrid: remove custom interpolation code by pbrubeck · Pull Request #5289 · firedrakeproject/firedrake

pbrubeck · 2026-07-28T22:17:50Z

Stack

Merge in this order, each PR retargets to main once the one above it lands:

# PR what

1 firedrakeproject/fiat#271 FInAT: select H(div)/H(curl) components with a Delta

2 firedrakeproject/fiat#268 FInAT: dual evaluate on each sub-element's own points

3 #5289 p-multigrid: remove custom interpolation

Removes ~1050 lines of hand-written interpolation machinery from
firedrake/preconditioners/pmg.py — StandaloneInterpolationMatrix,
MixedInterpolationMatrix, kronmxv, get_permutation_to_nodal_elements,
evaluate_dual and friends — and replaces the p-multigrid transfer operators with
the generic assemble(interpolate(TrialFunction(cV), fV)). The helpers that are still
needed move to firedrake/preconditioners/fdm.py.

Depends on firedrakeproject/fiat#268

Fixes #5391 by removing the transfer matrix cache

🤖 Generated with Claude Code

An element whose functionals do not all evaluate on the same points is a direct sum, and has a dual basis only on each of its sub-elements, not one weight tensor on one point set. Reconstructing it as a runtime Quadrature space only ever wanted the points, so ask for those directly. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Assembling a two-form Interpolate matrix-free passed the same bcs as both the row and the column bcs of the ImplicitMatrixContext, and left on_diag at its default of True. Neither holds for interpolation between two different spaces: applying the target space's bcs to the source side raised "Cofunction defined on incompatible FunctionSpace", and on_diag made multTranspose try to write the row values into the column vector. Split the bcs by the space they are defined on, as the assembled path already does, and set on_diag from whether the two spaces coincide. A bc on a component of a mixed space is defined on an IndexedProxyFunctionSpace rather than on the space itself, so compare against the top-level parent, which BCBase.function_space now returns on request. Coarsen the p-multigrid nullspace with a locally built interpolation matrix, rather than through getNestSubMatrix, which only the removed MixedInterpolationMatrix provided. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Installs firedrakeproject/fiat@pbrubeck/fix/dual-enriched over the pinned FIAT, so CI gets fiat#268 and the fiat#271 it sits on. This PR needs the dual evaluation those provide. Drop once fiat#271 and fiat#268 land on FIAT main. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

pbrubeck · 2026-08-26T15:55:56Z


    ibase = numpy.arange(bsize, dtype=node_map.values.dtype)
    return partial(vector_map, bsize, ibase), nel
+


This is custom code from pmg.py that is now only required by fdm.py

The dual basis of a restricted element is a Concatenate, and a Cofunction dual argument sums over the index that concatenates it. Forming that contraction first leaves the Concatenate indexed by a reduction index that no assignment variable carries, so unconcatenate has nothing to split it against and it reaches argument factorisation, which cannot break it up. Split the pair of the dual coefficient and the tabulation first, as assembly already does for coefficient evaluation, and contract each block over the basis indices of its own block. Interpolating between facet-restricted spaces, as p-multigrid does under FacetSplitPC, raised FactorisationError before this. The error escaped a PETSc callback, which left the preconditioner half built, and destroying it later segfaulted. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

connorjward · 2026-08-27T08:27:10Z

This is failing an awful lot of tests. Is it ready for review?

pbrubeck · 2026-08-27T08:29:05Z

This is failing an awful lot of tests. Is it ready for review?

I'll be fixing those today. I'll ask for review when it's passing. In principle it should be a small fix to make everything pass

connorjward · 2026-08-27T08:57:11Z

Can you check if this fixes #5391? I just debugged that down to it being (I think) to do with StandaloneInterpolationMatrix.

Every worker of the `tests/tsfc` session segfaults at its first `compile_form`, in `petsctools.cite` -> `PETSc.Sys.registerCitation`, because `PetscCitationsList` is still NULL: PETSc was never initialised. `petsc4py.lib.ImportPETSc` puts the extension module straight into `sys.modules`, bypassing the `petsc4py/PETSc.py` shim that calls `PETSc._initialize`. Once that has happened no later `from petsc4py import PETSc` initialises anything. The same fingerprint shows in the firedrake sessions: on `main` the conftest's `import pyadjoint` initialises PETSc before `firedrake/__init__.py` does, and `petsctools.init` warns that it is too late; on this branch that warning never appears. This does not reproduce locally, so record who calls `ImportPETSc` and report the state of PETSc once collection has imported every test module. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

This reverts commit 30edc16.

pbrubeck · 2026-08-27T09:50:11Z

Can you check if this fixes #5391? I just debugged that down to it being (I think) to do with StandaloneInterpolationMatrix.

It does fix it.

pbrubeck force-pushed the pbrubeck/remove-pmg-parloop branch from a79a5c0 to 2c9e9a1 Compare July 29, 2026 10:25

pbrubeck changed the base branch from main to pbrubeck/fix/dual-enriched July 29, 2026 10:26

pbrubeck added the base:main Run this PR using a main (dev) build label Jul 29, 2026

pbrubeck marked this pull request as ready for review July 29, 2026 10:31

pbrubeck force-pushed the pbrubeck/remove-pmg-parloop branch from 2c9e9a1 to 8b84e62 Compare July 29, 2026 10:33

pbrubeck force-pushed the pbrubeck/fix/dual-enriched branch from cf08365 to a9ee8fa Compare July 29, 2026 10:33

leo-collins reviewed Jul 29, 2026

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pbrubeck commented Jul 29, 2026

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pbrubeck mentioned this pull request Jul 29, 2026

Select H(div)/H(curl) components with a Delta firedrakeproject/fiat#271

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pbrubeck force-pushed the pbrubeck/remove-pmg-parloop branch from 8b84e62 to 41c33c8 Compare July 29, 2026 18:30

pbrubeck force-pushed the pbrubeck/fix/dual-enriched branch 2 times, most recently from 168ee7b to 6072eee Compare July 29, 2026 23:29

pbrubeck force-pushed the pbrubeck/remove-pmg-parloop branch from 3d81cdf to 33be7ba Compare July 29, 2026 23:29

pbrubeck changed the base branch from pbrubeck/fix/dual-enriched to pbrubeck/hdivcurl-delta July 29, 2026 23:33

pbrubeck force-pushed the pbrubeck/hdivcurl-delta branch from a992610 to 537d1b5 Compare August 18, 2026 22:22

pbrubeck force-pushed the pbrubeck/remove-pmg-parloop branch from 2cdcc16 to 59e617b Compare August 18, 2026 22:22

pbrubeck commented Aug 18, 2026

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pbrubeck commented Aug 24, 2026

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pbrubeck force-pushed the pbrubeck/remove-pmg-parloop branch from e9e3a1e to 59e617b Compare August 24, 2026 22:24

pbrubeck and others added 5 commits August 26, 2026 12:44

merge conflict

c79ceab

p-multigrid: remove custom interpolation code

cb0cec3

Update firedrake/functionspaceimpl.py

7cafe7e

pbrubeck force-pushed the pbrubeck/remove-pmg-parloop branch from 57c801d to fc8c4f9 Compare August 26, 2026 11:46

pbrubeck changed the base branch from pbrubeck/hdivcurl-delta to main August 26, 2026 11:46

pbrubeck force-pushed the pbrubeck/remove-pmg-parloop branch from fc8c4f9 to 8b12202 Compare August 26, 2026 11:58

pbrubeck commented Aug 26, 2026

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pbrubeck added 2 commits August 26, 2026 14:34

Update firedrake/functionspaceimpl.py

46bf90b

remove weakref cache

164c522

pbrubeck requested a review from connorjward August 26, 2026 15:34

pbrubeck added 2 commits August 26, 2026 16:44

Fix test

3b6cb6a

only take dual on the DualSpace

50e01d8

pbrubeck commented Aug 26, 2026

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pbrubeck added the LLM used An LLM was used in the production of this PR label Aug 26, 2026

pbrubeck and others added 2 commits August 27, 2026 10:23

Revert "DROP BEFORE MERGE - name what leaves PETSc uninitialised in CI"

46f419b

This reverts commit 30edc16.

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p-multigrid: remove custom interpolation code - #5289

p-multigrid: remove custom interpolation code#5289
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#	PR	what
1	firedrakeproject/fiat#271	FInAT: select H(div)/H(curl) components with a `Delta`
2	firedrakeproject/fiat#268	FInAT: dual evaluate on each sub-element's own points
3	#5289	p-multigrid: remove custom interpolation


		ibase = numpy.arange(bsize, dtype=node_map.values.dtype)
		return partial(vector_map, bsize, ibase), nel

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pbrubeck commented Jul 28, 2026 •

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