#include "petscdmcomposite.h" PetscErrorCode DMCompositeGetGlobalISs(DM dm,IS *is[])Collective on DMComposite
These could be used to extract a subset of vector entries for a "multi-physics" preconditioner
Use DMCompositeGetLocalISs() for index sets in the packed local numbering, and DMCompositeGetISLocalToGlobalMappings() for to map local sub-DM (including ghost) indices to packed global indices.
The output argument 'is' must be an allocated array of sufficient length, which can be learned using DMCompositeGetNumberDM().