makeringlatticeCIJ.m
3209cc2b0b1dmaster

makeringlatticeCIJ.m
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			function [CIJ] = makeringlatticeCIJ(N,K)
			%MAKERINGLATTICECIJ Synthetic lattice network
			%
			% CIJ = makeringlatticeCIJ(N,K);
			%
			% This function generates a directed lattice network with toroidal
			% boundary counditions (i.e. with ring-like "wrapping around").
			%
			% Inputs: N, number of vertices
			% K, number of edges
			%
			% Outputs: CIJ, connection matrix
			%
			% Note: The lattice is made by placing connections as close as possible
			% to the main diagonal, with wrapping around. No connections are made
			% on the main diagonal. In/Outdegree is kept approx. constant at K/N.
			%
			%
			% Olaf Sporns, Indiana University, 2005/2007

			% initialize
			CIJ = zeros(N);
			CIJ1 = ones(N);
			KK = 0;
			cnt = 0;
			seq = 1:N-1;
			seq2 = N-1:-1:1;

			% fill in
			while (KK<K)
			cnt = cnt + 1;
			dCIJ = triu(CIJ1,seq(cnt))-triu(CIJ1,seq(cnt)+1);
			dCIJ2 = triu(CIJ1,seq2(cnt))-triu(CIJ1,seq2(cnt)+1);
			dCIJ = dCIJ+dCIJ'+dCIJ2+dCIJ2';
			CIJ = CIJ + dCIJ;
			KK = sum(sum(CIJ));
			end;

			% remove excess connections
			overby = KK-K;
			if(overby>0)
			[i,j] = find(dCIJ);
			rp = randperm(length(i));
			for ii=1:overby
			CIJ(i(rp(ii)),j(rp(ii))) = 0;
			end;
			end;