function G = gridgraph(n)
n1 =  floor(sqrt(n));
n2 =  ceil(sqrt(n));

G = zeros(n);
for i=1:n1
  for j=1:n2
    % connect (i,j) to right neighbor
    G = connect(G,i,j,i,j+1,n1,n2);
    % connect (i,j) to lower neighbor
    G = connect(G,i,j,i+1,j,n1,n2);
  end
end
return


function G = connect(G,i1,j1,i2,j2,n1,n2)
if (max(i1,i2)<=n1) & (max(j1,j2)<=n2)
  ij1 = coord2ind([i1 j1],[n1 n2]);
  ij2 = coord2ind([i2 j2],[n1 n2]);  
  G(ij1,ij2) = 1;
  G(ij2,ij1) = 1;  
end
return