function [G,XY] = getgraph();
% a sample graph

XY = [0 2;
      -1 1;
      0 1;
      1 1;
      2 1;
      -1 0;
      0 0;
      -1 -1;
      0 -1;
      1 -1;
      0 -2];

Edg = [1 2;
       1 3;
       1 4;
       1 5;
       2 3;
       3 4;
       4 5;
       2 6;
       3 7;
       4 7;
       5 7;
       6 7;
       6 8;
       7 9;
       7 10;
       8 9;
       9 10;
       8 11;
       9 11;
       10 11];

nnod = size(XY,1);
G = sparse(Edg(:,1),Edg(:,2),1,nnod,nnod);
G = spones(G+G');
G = G-spdiags(diag(G),0,nnod,nnod);