probe a graph colouring

gistfile1.matlab

function [V,colours] = probe( colours)
%% function [V] = probe(A,p)
%   Creates a probing matrix based on a graph colouring of A using the
%   algorithm in "J. Tang and Y. Saad, A probing method for computing the diagonal of the matrix
%   inverse" (2010).
%
%   REQUIRES: Matgraph toolbox http://www.ams.jhu.edu/~ers/matgraph/
%
%    Input:  colours   - A graph colouring (of A^p probably)
%            
%   Output: V   - Probing matrix V
%
%   Author: Daniel Simpson
%   Date: 26/08/2010
%
%   There is no waranty or guarentee of any kind associated with this code.
%%

  


%Calculate adjacency graph of the pth nearest neighbour graph.
n = length(colours);



ncolours = max(colours);

V = zeros(n,ncolours);


        for i = 1:ncolours
            

            V(colours==i,i)=sign(randn(sum(colours==i),1));
        end
% keyboard;

% free(g);