function [G,XY] = getgraphStar(nnod);
% creates the graph of "ring" topology with (nnod) nodes:

al = 0:2*pi/(nnod-1):2*pi-1e-10;
XY = [cos(al),0; sin(al),0]';
b=[];
for i=1:nnod-1,b=[b,nnod];i=i+1;end
G = sparse([b],[1:nnod-1],1,nnod,nnod);
G = spones(G+G');
G = G-spdiags(diag(G),0,nnod,nnod);