Need help with my matlab code. I\'m basically trying to find the poles of the bu

Question

Need help with my matlab code. I'm basically trying to find the poles of the butterworth low pass filter without using the butter() function.

For my a vector it has to be a=[1 sqrt(2) 1]; but instead i'm getting a=3.4142 . Can someone help me tell me why code it's not giving me the correct a vector?

Thank you

clc
clear all
w=logspace(-1,4,1000);
%p represents poles of the filter
p0=exp(1*i*pi/4);
p1=exp(1*i*3*pi/4);
p2=exp(1*i*5*pi/4);
p3=exp(1*i*7*pi/4);
%real function gets the real poles
real(p0);
real(p1);
real(p2);
real(p3);

% i used p1 and p2 because we need the poles in left hand plane which are negative

conv([1-p1],[1-p2]);
a=real(conv([1-p1],[1-p2]));%a needs to be [1 sqrt(2) 1]
b=[1];
freqs(b,a,w)

Explanation / Answer

Ans)

I have corrected the code ,the error is you missed the space when defining a vector i.e [1 -p1] instead of [1-p1]

corrected code here

==============

clc
clear all
w=logspace(-1,4,1000);
%p represents poles of the filter
p0=exp(1*1i*pi/4);
p1=exp(1*1i*3*pi/4);
p2=exp(1*1i*5*pi/4);
p3=exp(1*1i*7*pi/4);
%real function gets the real poles
real(p0);
real(p1);
real(p2);
real(p3);
% i used p1 and p2 because we need the poles in left hand plane which are negative
conv([1 -p1],[1 -p2]);
a=real(conv([1 -p1],[1 -p2]));%a needs to be [1 sqrt(2) 1]
a
b=[1];
freqs(b,a,w)

=============================

Result in command window

a =

1.0000 1.4142 1.0000

===========

I guess that is the answer you anticipated as in question

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