Hi there,
I am using MPI_Reduce with a user-defined type as follow
#define N 100
int src[N], dest[N];
MPI_Op myOp;
MPI_Datatype DT;
void fun(int *in, int *inout, int *len, MPI_Datatype *dptr)
{ int i;
for (i=0; i<*len; ++i)
{
*inout = *in + 2*(*inout);
*in++; *inout++;
}
}
int main(int argc,char *argv[])
{
...
MPI_Type_contiguous( N, MPI_INT, &DT );
MPI_Type_commit( &DT );
MPI_Op_create( (void *)fun, 0, &myOp );
MPI_Reduce( &src[0], &dest[0], N, MPI_INT, myOp, 0, MPI_COMM_WORLD );
MPI_Reduce( &src[0], &dest[0], 1, DT, myOp, 0, MPI_COMM_WORLD );
MPI_Op_free(&myOp);
MPI_Type_free(&DT);
...
return 1;
}
In the first invoked of MPI_Reduce, nothing goes wrong. However, I would
like to define
a little bit complicated type. For testing, I just use a contiguous type
instead. DT is
just the type contains N contiguous units as whole. So, the 'count'
parameter of MPI_Reduce
should be 1 instead of N when DT is given as type rather than MPI_INT
logically. However,
I find that in the case ONLY ONE ELEMENTS of the source buffer will be
picked to take part
in the calculation, i.e. the *len parameter of fun() is ONE! How is that
happen!?
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