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FEniCS / ufl

UFL - Unified Form Language
https://fenicsproject.org
GNU Lesser General Public License v3.0
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`FormSum.coefficients()` should be ordered deterministically #242

Closed JHopeCollins closed 10 months ago

JHopeCollins commented 10 months ago

Form.coefficients() and FormSum.coefficients() both use set to produce a unique collection of the coefficients. However, set does not have deterministic ordering. Form._analyze_form_arguments() uses sorted to make sure that the ordering is deterministic across MPI ranks and across multiple programme executions, but FormSum._analyze_form_arguments() doesn't.

This means that the ordering is sometimes different between different MPI ranks, which causes parallel hangs in MG code when a Function is sent to inject on one rank and a Cofunction is sent to restrict on another rank.

This PR just adds orders FormSum.coefficients() in the same way as Form.coefficients()

JHopeCollins commented 10 months ago

Closed here and reopened on the Firedrake/ufl https://github.com/firedrakeproject/ufl/pull/47