# MPI_Isend

Begins a nonblocking send

## Synopsis

    #include "mpi.h"
    int MPI_Isend( void *buf, int count, MPI_Datatype datatype, int dest, int tag,
            MPI_Comm comm, MPI_Request *request )

## Input Parameters

| buf | initial address of send buffer (choice)
| count | number of elements in send buffer (integer)
| datatype | datatype of each send buffer element (handle)
| dest | rank of destination (integer)
| tag | message tag (integer)
| comm | communicator (handle)

## Output Parameter

request
  communication request (handle)

## Notes for Fortran

All MPI routines in Fortran (except for `MPI_WTIME` and `MPI_WTICK`) have an additional argument `ierr` at the end of the argument list. `ierr` is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the `call` statement.

All MPI objects (e.g., `MPI_Datatype`, `MPI_Comm`) are of type `INTEGER` in Fortran.

## Errors

All MPI routines (except `MPI_Wtime` and `MPI_Wtick`) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with `MPI_Errhandler_set`; the predefined error handler `MPI_ERRORS_RETURN` may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error.

MPI_SUCCESS
  No error; MPI routine completed successfully.

MPI_ERR_COMM
  Invalid communicator. A common error is to use a null communicator in a call (not even allowed in `MPI_Comm_rank`).

MPI_ERR_COUNT
  Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.

MPI_ERR_TYPE
  Invalid datatype argument. May be an uncommitted MPI_Datatype (see `MPI_Type_commit`).

MPI_ERR_TAG
  Invalid tag argument. Tags must be non-negative; tags in a receive (`MPI_Recv`, `MPI_Irecv`, `MPI_Sendrecv`, etc.) may also be `MPI_ANY_TAG`. The largest tag value is available through the the attribute `MPI_TAG_UB`.

MPI_ERR_RANK
  Invalid source or destination rank. Ranks must be between zero and the size of the communicator minus one; ranks in a receive (`MPI_Recv`, `MPI_Irecv`, `MPI_Sendrecv`, etc.) may also be `MPI_ANY_SOURCE`.

MPI_ERR_INTERN
  This error is returned when some part of the MPICH implementation is unable to acquire memory.

Location:isend.c