Spy plot with partitioning.

  SPYPART(S,rp,cp) plots the sparsity pattern of a matrix S,

  with lines marking a block partition described by 

  rp (rows) and cp (columns).

  If S is square, cp may be omitted and defaults to rp.



  Partitions are specified as in the output of DMPERM2AMLGCO:

  There are length(rp)-1 row blocks, of sizes diff(rp), with rp(1)=1.