title: C MPI multiple dynamic array passing
body: <p>I'm trying to <code>ISend()</code> two arrays: <code>arr1,arr2</code> and an integer <code>n</code> which is the size of <code>arr1,arr2</code>. I understood from this <a href="https://stackoverflow.com/questions/10419990/creating-an-mpi-datatype-for-a-structure-containing-pointers">post</a> that sending a struct that contains all three is not an option since <code>n</code> is only known at run time. Obviously, I need <code>n</code> to be received first since otherwise the receiving process wouldn't know how many elements to receive. What's the most efficient way to achieve this without using the blokcing <code>Send()</code> ? </p>