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.
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Verify that the datatype works by communicating a single column/row.
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Try to send to columns / rows. What happens? Can you explain why?
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Create a new datatype with resized extent, so that communicating multiple columns / rows succeeds.
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Try to scatter columns / rows with
MPI_Scatter