Some collective mpi operations allow the user to re-use the input buffer as the output buffer (MPI_IN_PLACE). I did not find that functionality in boost::mpi and filed a ticket (https://svn.boost.org/trac/boost/ticket/6704) along with a patch for a possible implementation for all_reduce and the associated testing. What is the best way to get some input regarding that proposed patch ? (the ticket itself has been untouched for 3 months now) Best regards, -- Alain Miniussi Responsable Tech. Centre de Calcul Haute Performance Observatoire de la Côte d'Azur - BP 4229 - 06304 Nice Cedex 4 tel: +33 4 92 00 30 09 https://crimson.oca.eu