[ET Trac] [Einstein Toolkit] #920: CarpetLib::check_communication_schedule fails in 2D output routines

[Einstein Toolkit]

#920: CarpetLib::check_communication_schedule fails in 2D output routines
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  Reporter:  rhaas   |       Owner:  eschnett
      Type:  defect  |      Status:  new     
  Priority:  minor   |   Milestone:          
 Component:  Carpet  |     Version:          
Resolution:          |    Keywords:          
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Comment (by eschnett):

 To clarify: This test checks whether all MPI processes send and receive
 consistent amounts of data. It uses MPI_Alltoall to exchange this
 information, which is otherwise implicitly obtained from the communication
 schedule and not explicitly checked.

 However, CarpetIOASCII and CarpetIOHDF5 use an optimised communication
 strategy where only pairs of processes communicate; in particular, process
 N sends data to process 0 for output. In this case, the MPI_Alltoall
 obviously fails.

 The solution is to tell the commstate class which processes are going to
 be involved.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/920#comment:1>
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