[b a]=cheby1(n,Rp,Wn,'s') ;
FRF_dB = 20*log10(abs(h));
[f1,s0_pos,f2,s0_neg] = crossing_V7(FRF_dB2,w,-3);
W = [W(1)*cor_coeff1 W(2)*cor_coeff2];
[b a]=cheby1(n,Rp,W,'s') ;
FRF_dB2 = 20*log10(abs(h));
[f11,s0_pos,f22,s0_neg] = crossing_V7(FRF_dB2,w,-3);
semilogx(w,FRF_dB,'b',w,FRF_dB2,'r',f11,s0_pos,'dr',f22,s0_neg,'dr');
function [t0_pos,s0_pos,t0_neg,s0_neg] = crossing_V7(S,t,level,imeth)
error(nargchk(1,4,nargin));
if nargin < 2 | isempty(t)
elseif length(t) ~= length(S)
error('t and S must be of identical length!');
S1 = S(1:end-1) .* S(2:end);
if strcmp(imeth,'linear')
if abs(S(ind(ii))) > eps*abs(S(ind(ii)))
NUM = (t(ind(ii)+1) - t(ind(ii)));
DEN = (S(ind(ii)+1) - S(ind(ii)));
slope_sign(ii) = sign(slope);
t0(ii) = t0(ii) - S(ind(ii)) * slope;
ind_pos = find(sign(slope_sign)>0);
ind_neg = find(sign(slope_sign)<0);