Hi, It seems creating communicator with cartesian topology is not supported by boost mpi (that topology can be probed, though). One can only create such a topology with MPI_Cart_create and then pass the handle to the boost ctor. Is there a reason for that ? (Should I stay away from that topology when using boost) Best regards -- Alain Miniussi ---- mail: alain.miniussi@oca.eu SIT https://sitweb.oca.eu tel: +33 4 92 00 30 09 CRIMSON https://crimson.oca.eu