MATSELL = "sell" - A matrix type to be used for sparse matrices. This matrix type is identical to MATSEQSELL when constructed with a single process communicator,
and MATMPISELL otherwise. As a result, for single process communicators,
MatSeqSELLSetPreallocation is supported, and similarly MatMPISELLSetPreallocation is supported
for communicators controlling multiple processes. It is recommended that you call both of
the above preallocation routines for simplicity.