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()
Form.coefficients()andFormSum.coefficients()both usesetto produce a unique collection of the coefficients. However,setdoes not have deterministic ordering.Form._analyze_form_arguments()usessortedto make sure that the ordering is deterministic across MPI ranks and across multiple programme executions, butFormSum._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
Functionis sent toinjecton one rank and aCofunctionis sent torestricton another rank.This PR just adds orders
FormSum.coefficients()in the same way asForm.coefficients()