function [z,p,k] = MinesButtap(N)
% returns zeros, poles, HF gain of the normalized Butterwort filter
% of order N

% compute angles in the first quadrant, zero being excluded
if mod(N,2) == 0
    % N/2 roots in first quadrant, zero excluded
    ro = [0:(N/2 -1)];
    ro1 = ones(size(ro))*0.5;
    ro = ro + ro1;
    ro = ro .* (pi/N); % root angles strictly in first quadrant
else
    N1 = floor(N/2); % note that N/2 is not an integer
    ro = [1:N1].*(pi/N); % note that root -1 must be added at the end
end
% compute roots of the unit in the first quadrant
ro1 = exp(i*ro);
% symmetry w/r to the imaginary axis
p1 = -real(ro1)+i*imag(ro1);
% conjugate poles
p2 = conj(p1);
if mod(N,2) == 0
    p = [p1 p2];
else
    p = [p1 -1 p2];
end
z = [];
k = 1;
        

