function spypart(S, rp, cp);

%SPYPART 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 DMPERM:

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

%   Copyright (c) 1984-98 by The MathWorks, Inc.

%   $Revision: 5.3 $  $Date: 1997/11/21 23:27:12 $

if (nargin < 3), cp = rp; end

spy(S)

hold on

[m,n] = size(S);

if length(rp) > 2

   k = length(rp)-2;

   X = [zeros(1,k); n+ones(1,k)];

   Y = rp(2:k+1) - 0.5;

   Y = [Y; Y];

   plot(X,Y,'w-') 

end

if length(cp) > 2

   k = length(cp)-2;

   X = cp(2:k+1) - .5;

   X = [X; X];

   Y = [zeros(1,k); m+ones(1,k)];

   plot(X,Y,'w-') 

end

axis('ij')

hold off