How do you write data when one process doesn't have or need to write data?

The following examples show how to write data collectively and independently when one process doesn't have data or does not need to write data.

• coll_test.c - Uses H5Sset_none to tell H5Dwrite call that there will be no data. 4-th process HAS to participate since we are in a collective mode. 
• ind_test.c - Specifies which process writes data. H5Dwrite is not called by the 4-th process at all in this case; this approach will work only when independent mode is used.