function C=getC(N)
  if N==2
    C=[0,1;-1,-1];
  else
    Y=zeros(N,N);
    Y(1,N)=-1;
    Y(N,2)=-1;
    Y(N/2, 1)=-1;
    Y(2:N-1,2:N-1)=getC(N-2);
    C=Y;
end
