The MPI 2-1 standard says: "MPI_PROC_NULL is a valid target rank in the MPI RMA calls MPI_ACCUMULATE, MPI_GET, and MPI_PUT. The effect is the same as for MPI_PROC_NULL in MPI point-to-point communication. After any RMA operation with rank MPI_PROC_NULL, it is still necessary to finish the RMA epoch with the synchronization method that started the epoch."
Unfortunately, MPI_Accumulate() is not quite the same as point-to-point, as a reduction is involved. Suppose you make this call (let me abuse and use keyword arguments): MPI_Accumulate(..., target_rank=MPI_PROC_NULL, target_datatype=MPI_BYTE, op=MPI_SUM, ...) IIUC, the call fails (with MPI_ERR_OP) in Open MPI because MPI_BYTE is an invalid datatype for MPI_SUM. But provided that the target rank is MPI_PROC_NULL, would it make sense for the call to success? -- Lisandro Dalcín --------------- Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC) Instituto de Desarrollo Tecnológico para la Industria Química (INTEC) Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) PTLC - Güemes 3450, (3000) Santa Fe, Argentina Tel/Fax: +54-(0)342-451.1594