function [CIJ] = makelatticeCIJ(N,K)

% inputs:
%           N        number of vertices
%           K        number of edges
% outputs:
%           CIJ      connection matrix
%
% makes one lattice CIJ matrix, with size = N,K. The lattice is made by
% placing connections as close as possible to the main diagonal, without
% wrapping around, so it is NOT a ring. 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;

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