Problem with polyfit and polyval

Kshitij Singh answered . 2025-07-03 22:19:50

 
D = load('Philippe Amp.mat');
Freq = D.Amp(:,1);                                              % Hz Frequency Vector
Vi = D.Amp(:,3);
Vo = D.Amp(:,4);
H = Vo./Vi;                                                     % Amplitude Transfer Function
Phase = D.Amp(:,4);
W = Freq/max(Freq)*pi;                                          % Radian Frequency Vector

figure(1)                                                       % Look At The Data
subplot(2,1,1)
plot(Freq,Vi,  Freq,Vo)
grid
subplot(2,1,2)
plot(Freq, Phase)
grid

figure(2)
subplot(2,1,1)
plot(Freq, 20*log10(H))
ylabel('Magnitude (dB)')
grid
axis([xlim    -40  0])
subplot(2,1,2)
plot(Freq, Phase)
ylabel('Phase (degrees)')
grid

Hc = H .* exp(1i*pi*Phase/180);                                 % Create Complex Frequency Response
Hc(1) = interp1(Freq(2:end),Hc(2:end), 0, 'spline','extrap');   % Replace Initial ‘NaN’ Value

OrdNum = 3;
OrdDen = 5;
[b,a] = invfreqz(Hc, W, OrdNum, OrdDen);                        % Transfer Function Coefficients

figure(3)
freqz(b, a, 4096)                                               % Bode Plot

figure(4)
impz(b, a)                                                      % Impulse Response

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