><code>MPI_Alltoall</code> is defined by the MPI standard as:
</p>
<div class="example">
<pre class="example">int MPI_Alltoall(void *sendbuf, int sendcount, MPI_Datatype sendtype, 
                 void *recvbuf, int recvcnt, MPI_Datatype recvtype, 
                 MPI_Comm comm);
</pre></div>

<p>In particular, for <code>double*</code> arrays <code>in</code> and <code>out</code>,
consider the call:
</p>
<div class="example">
<pre class="example">MPI_Alltoall(in, howmany, MPI_DOUBLE, out, howmany MPI_DOUBL