================================
Scatter operations with overlaps                               [TOC]
================================

To accommodate the Jacobi solver, it would be
helpful to support overlapping sections.

Exercise
========

Extend `scatter_by_block` and `gather_by_block` by adding an optional
parameter `overlap` that specifies the size of the border. Please
consider that in case of `overlap > 0` the scatter and gather operations
are no longer symmetrical as `scatter_by_block` sends overlapping
regions at least twice while `gather_by_block` sends just the inner
sections.

---- CODE (type=cpp) ----------------------------------------------------------
template<typename T,
   template<typename> class MA,
   template<typename> class MB,
   Require<Ge<MA<T>>, Ge<MB<T>>> = true>
int scatter_by_block(const MA<T>& A, MB<T>& B, int root,
      MPI_Comm grid, int dims[2], int coords[2], int overlap = 0) {
   /* ... */
}

template<typename T,
   template<typename> typename MA,
   template<typename> typename MB,
   Require<Ge<MA<T>>, Ge<MB<T>>> = true>
int gather_by_block(const MA<T>& A, MB<T>& B, int root,
      MPI_Comm grid, int dims[2], int coords[2], int overlap = 0) {
   /* ... */
}
-------------------------------------------------------------------------------

Source code
===========

Following source code is available for testing:

:import:session07/scatter-gather5.cpp

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