[mpich-discuss] Why do predefined MPI_Ops function elementwise in MPI_Accumulate, but not in MPI-1 routines?

[Rajeev Thakur]

Probably not. But someone would have to go back and add that exception to the definition of MPI_Reduce.

On Apr 23, 2012, at 9:24 PM, Jed Brown wrote:

> On Mon, Apr 23, 2012 at 21:20, Rajeev Thakur <thakur at mcs.anl.gov> wrote:
> One reason is that MPI_Accumulate allows only a restricted form of derived datatype, where all basic elements are of the same type. In MPI_Reduce you can pass any crazy datatype and you get to define the reduction operation for that.
> 
> Is it somehow expensive to remember/determine that the datatype consists only of basic types, such that MPI_Reduce can process it in the same way that MPI_Accumulate does?
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