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README.md

Modifying extent

When the datatype contains gaps in the beginning or in the end, one might need to modify the extent of the datatype.

Starting from skeleton.c or skeleton.F90, create a vector datatype for sending a column (C) or row (Fortran) of a matrix.

  1. Verify that the datatype works by communicating a single column/row.

  2. Try to send multiple columns / rows. What happens? Can you explain why?

  3. Create a new datatype with resized extent, so that communicating multiple columns / rows succeeds.

  4. Generalize the code to multiple processes and scatter columns / rows with MPI_Scatter collective. Define a new array for the receive buffer and print it out on all ranks.