//int MPI_Allreduce(void *sbuf, void *rbuf, int count, MPI_Datatype dtype, MPI_Op op, MPI_Comm comm)
MPI_Allreduce(&sx, x, 1, MPI_DOUBLE, MPI_SUM, MPI_COMM_WORLD);
sx = x[0]; //FIXME : x[0] or x[1] => x[0] because fortran starts with 1
//int MPI_Allreduce(void *sbuf, void *rbuf, int count, MPI_Datatype dtype, MPI_Op op, MPI_Comm comm)
MPI_Allreduce(&sx, x, 1, MPI_DOUBLE, MPI_SUM, MPI_COMM_WORLD);
sx = x[0]; //FIXME : x[0] or x[1] => x[0] because fortran starts with 1