Scattered indices in MPI

Question

I'm trying to divide up an array between processors such that each one takes points from different parts in the array. For example, if

A = {1, 2, 3, 4, 5, 6, 7, 8}

and I'm using 2 processors, I want P₁ to handle {1, 3, 5, 7}, and P₂ to handle {2, 4, 6, 8}.

When scaling up to very large numbers of points (millions) and processors (128), this is tricky. In previous versions of my function, I simply gave P₁ the first chunk of points, P₂ the next chunk, and so on (which is easy with MPI_gatherv).

Is there some way to use MPI_gatherv to make this work, or a way to use MPI_send and MPI_receive to achieve it? The trouble with MPI_gatherv is that while you can specify indices for processors to send to, it still puts all of P₁ before P₂ before P₃ etc.