Draft: Protect calls to ParMETIS by HAVE_PARMETIS

Summary

ParMETIS can only be used if 1. the parmetis header parmetis.h is included and 2. the parmetis library is linked. IF this is the case, the compile definition HAVE_PARMETIS is set. This MR check for this define on all ParMETIS calls.

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• b044c22f - Protect calls to ParMETIS by HAVE_PARMETIS

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• 1cd33cc8 - Add error message if ParMETIS is not found

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resolved all threads

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• 91840fcd - Add error message if ParMETIS is not found

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Just for the record: When is graphRepartition() or commGraphRepartition() actually called?

MatrixHierarchy<...>::build(criterion) {
 if(
#if HAVE_PARMETIS
      /* some_condition */
#else
      false
#endif
      || criterion.accumulate()==atOnceAccu
    ) 
  {
    repartitionAndDistributeMatrix(...);
  }

  //...
  /* another call to repartitionAndDistributeMatrix() protected by several conditions
     but with nparts = 1 */
}

with repartitionAndDistributeMatrix() overloaded for SequentialInformation (just an error message) and other Information calling commGraphRepartition() if #if AMG_REPART_ON_COMM_GRAPH, otherwise graphRepartition().

Thus, the graphRepartition() is only called if ParMETIS is available, or a specific accumulation criterion is set. (Default is successiveAccu). Inside of graphRepartition() there is another check for ParMETIS:

#if !HAVE_PARMETIS 
  nparts=1;
#else
if(nparts>1) {
  ParMETIS_V3_PartKway(...);
}
#endif

and inside commGraphRepartition() the strategy is a bit different, there nparts is not set to 1, but we have to set another compile flag:

#if !HAVE_PARMETIS 
// ...
#else
#if PARALLEL_PARTITION
  ParMETIS_V3_PartKway(...);
#endif
#endif

marked this merge request as draft

The call to ParMETIS_V3_PartKway is actually already protected. It is just a bit difficult to find out, since there are up to 4-5 levels of nested preprocessor conditions without any comments. The reason why I got linker errors is, because in dune-common the #define HAVE_PARMETIS 1 was set independent of whether it was linked or not. This is now fixed with dune-common!1205 (merged)

Sorry for the noise. I will close this MR.

closed