Thank you for the excellent software! Not a critical issue, by any means, but just bringing to your attention that the man pages in 4.0.0 look like something didn't go quite right during generation; it has the function signature for QMPI_Send() rather than MPI_Send() and some extra preprocessor statements. [ From 4.0.0 .tar.gz from mpich.org ] MPI_Send(3) MPI MPI_Send(3) NAME MPI_Send - Performs a blocking send SYNOPSIS #ifdef ENABLE_QMPI #ifndef MPICH_MPI_FROM_PMPI int QMPI_Send(QMPI_Context context, int tool_id, const void *buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm) MPICH_API_PUBLIC [...] [ From 3.4.3 .tar.gz from mpich.org ] MPI_Send(3) MPI MPI_Send(3) NAME MPI_Send - Performs a blocking send SYNOPSIS int MPI_Send(const void *buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm) [...] You can see this in the mpich-hosted man pages, too: https://www.mpich.org/static/docs/latest/www3/MPI_Send.html Thanks, - Eric