# cannot use element wise operator in frequency response?

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SimTec le 24 Août 2022
Commenté : Bruno Luong le 24 Août 2022
Hi guys,
I am trying to get the requency response of the averaging FIR filter using the element wise operator, code below:
Fs=8e3; % sampling frequency
Fc=170; % cutoff frequency
alpha=1-2*pi*Fc/Fs;
nb=round(log2(1/(1-alpha))); % number of shift to the right correspending to multiplication by alpha
NbPoints=1000;
Ndec=Fs/2/1000;
Fstart=1;
i=1:Ndec*NbPoints;
freq=Fstart*10.^(i/NbPoints);
H_f=(1-alpha)*cos(pi.*freq/Fs)/sqrt(1+(alpha^2)-2*alpha*cos(2*pi.*freq/Fs));
semilogx(freq,20*log10(abs(H_f)))
the problem the H_f provides me only one output and not the vector result. how can I fix this.
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Bruno Luong le 24 Août 2022
The division "/" before sqrt is NOT elemetwise division "./".

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### Réponse acceptée

Abderrahim. B le 24 Août 2022
Fs=8e3; % sampling frequency
Fc=170; % cutoff frequency
alpha=1-2*pi*Fc/Fs;
nb=round(log2(1/(1-alpha))); % number of shift to the right correspending to multiplication by alpha
NbPoints=1000;
Ndec=Fs/2/1000;
Fstart=1;
i=1:Ndec*NbPoints;
freq=Fstart*10.^(i/NbPoints)
freq = 1×4000
1.0023 1.0046 1.0069 1.0093 1.0116 1.0139 1.0162 1.0186 1.0209 1.0233 1.0257 1.0280 1.0304 1.0328 1.0351 1.0375 1.0399 1.0423 1.0447 1.0471 1.0495 1.0520 1.0544 1.0568 1.0593 1.0617 1.0641 1.0666 1.0691 1.0715
H_f=(1-alpha)*cos(pi.*freq/Fs)./sqrt(1+(alpha^2)-2*alpha*cos(2*pi.*freq/Fs))
H_f = 1×4000
1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000
semilogx(freq,20*log10(abs(H_f)))
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