[Trilinos-Users] MueLu: proposed requirement for application matrix row and column maps

Jonathan Hu jhu at sandia.gov
Wed Sep 20 16:41:44 EDT 2017

Trilinos Users,

     [If you are not interested in the MueLu multigrid solver package, 
please ignore.]

This is advanced notice that the MueLu package developers are planning 
to explicitly require that the row map of any application-supplied 
matrix be "locally fitted" to the matrix column map, on each MPI 
process.  A map M1 is said to be locally fitted to a map M2 on an MPI 
process if all of the global indices in M1 appear at the beginning of M2 
and in the same order as in M1.  Fittedness is a local property with at 
most linear cost.  Checking that it holds for all MPI processes 
necessitates a global reduction.

After this requirement goes into force, the MueLu preconditioner 
constructors will check whether any user-supplied matrix's row map is 
locally fitted to its column map.  If the maps are not locally fitted on 
all MPI processes, an exception will be thrown.

Application developers can determine whether their matrices meet this 
new requirement by using the method 
Tpetra::Details::isLocallyFitted(rowmap,columnmap) [doxygen link 

If you believe that this change will cause undue hardship for your 
application, please contact me directly as soon as possible, and no 
later than Friday, October 6, 2017.

Jonathan Hu (for the MueLu development team)
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