function fr(r1, r2, r3, p1, p2, p3)
p = poly([r1*exp(i*p1) r2*exp(i*p2) r3*exp(i*p3) r1*exp(-i*p1) r2*exp(-i*p2) r3*exp(-i*p3)]);
f = ((1:100001)-1)*2*pi/100000;
ef = exp(i*f);
resp = polyval(p,ef);
figure
plot(f, 20*log10(abs(resp)))
title('frequency response of filter')
xlim([0, pi])
figure
plot(f, angle(resp))
title('phase response of filter')
xlim([0, pi])
figure
freqz(p)
end

function ir(r1,r2,r3,p1,p2,p3)
p = poly([r1*exp(i*p1) r2*exp(i*p2) r3*exp(i*p3) r1*exp(-i*p1) r2*exp(-i*p2) r3*exp(-i*p3)]);
figure
impz(p)
end

function frr(r1, r2, r3, p1, p2, p3, ndigits)
p = poly([r1*exp(i*p1) r2*exp(i*p2) r3*exp(i*p3) r1*exp(-i*p1) r2*exp(-i*p2) r3*exp(-i*p3)]);
p = round(p, ndigits);
f = ((1:100001)-1)*2*pi/100000;
ef = exp(i*f);
resp = polyval(p,ef);

figure
zplane(roots(p), [])

figure
freqz(p)
end