Hr_type3 function in matlab

I am trying to design a type 3 FIR filter and generate its amplitude response from the function Hr_type3 (mentioned in Digital processing in matlab by Proakis), but getting an error of unknown function or variable.

Can any one help me on this?

I am trying to run this code.

M = 21;
alpha = (M-1)/2;
n = 0:M-1;
hd = (cos(pi*(n-alpha)))./(n-alpha);
hd(alpha+1) = 0;
w_ham = (hamming(M))';
h = hd .* w_ham;
[Hr,w,P,L] = Hr_Type3(h);

Answer 1

[Sukrut Tamhankar]

Hr_Type3() is not an in-built function in MATLAB for FIR Filter design. Hence, before directly calling this function, you need to define this function in one separate M-file and save that file with the function name (i.e. Hr_Type3.m in this case) in the same folder in which the above MATLAB script is present.

Hence, the function definition (Hr_Type3.m file) looks like below (Reference: Digital Signal Processing Using MATLAB V.4 by John G. Proakis):

function [Hr,w,c,L] = Hr_Type3(h)
    M=length(h);
    L=(M-1)/2;
    c=[2*h(L+1:-1:1)];
    n=[0:1:L];
    w=[0:1:500]'*pi/500;
    Hr=sin(w*n)*c';
end

Then, when you call this function in your script using following line of code, you will not face any error message:

[Hr,w,P,L] = Hr_Type3(h);

I hope this information helps in resolving the issue.