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Array Count Arguments.

The mpiJava binding often omits array size arguments, because they can be picked up within the function by reading the length member of the array argument. A major exception is for message buffers, where an explicit count is always given. In the mpiJava, message buffers have explicit offset and count arguments whereas other kinds of array argument typically do not. Message buffers aside, typical array arguments to MPI functions (eg, vectors of request structures) are small arrays. If subsections of these must be passed to an MPI function, the sections can be copied to smaller arrays at little cost. In contrast message buffers are typically large and copying them is expensive, so it is worthwhile to pass the extra arguments. Also, if derived data types are being used, the required value of the count argument is always different to the buffer length.

Bryan Carpenter 2004-06-09