[petsc-dev] DMplex: Natural Ordering and subDM

[Blaise A Bourdin]

Hi,
I am fighting with natural ordering in DMplex with multi-fields / multi components DM.
I need to read / write files in a distribution-independent ordering. The natural way to do so is to define the natural ordering as that of the file, then call DMPlexGlobalToNaturalBegin/End before VecView:
The pseudo code would be

  DMPlexCreateFromFile(PETSC_COMM_WORLD,ifilename,interpolate,&dmUAS);
  // create default section associated with a complicated layout of multiple fields 
  // (U,\alpha,\sigma)
  DMSetUseNatural(dmUAS,PETSC_TRUE);
  DMPlexDistribute(dmUAS,0,&migrationSF,&dmDist);

  DMGetGlobalVector(dmDist,&UAS);
  DMGetGlobalVector(dmDist,&UASNatural);
  DMPlexGlobalToNaturalBegin(dmDist,UAS,UASNatural);
  DMPlexGlobalToNaturalEnd(dmDist,UAS,UASNatural);
  // Do my I/O stuff using UASNatural

If I try to do the same thing one field at a time, things break:
Say that I get the subDM for the first field (U):

  DMCreateSubDM(dmDist,1,&fieldU,&ISU,&dmU);

Then dmU->useNatural is PETSC_FALSE and  I cannot compute dmU->sfnatural using DMPlexCreateGlobalToNaturalSF since I do not have the “sequential” version of dmU.

What is the proper way to handle this situation? Creating sequential subDMs and calling DMDistribute on each of them is ugly and possibly costly.

Regards,

Blaise

-- 
Department of Mathematics and Center for Computation & Technology
Louisiana State University, Baton Rouge, LA 70803, USA
Tel. +1 (225) 578 1612, Fax  +1 (225) 578 4276 http://www.math.lsu.edu/~bourdin