Why is my loop not working?

Hi,

I have a code, where I am using elliptical bandpass filter and trying to filter some signals and calculate total power for them, and this should happen for cut-off frequency starting from 50 upto 5000 with a step size of 50. My code works fine if I run for each frequency seperately, but when I run inside all loops to get values all at once, I receive this problem:

>>Total_power
    2.5945

Error using ellip (line 60)
Wn must be a one or two element vector.

Error in total_power (line 19)
[b,a]=ellip(1,20,25,[a 5000]/(fs/2),'bandpass');

My code is as follows:

close all;

%Filter design
a=0;
b=10;
%x=zeros[];

for k=1:100 %%here loop runs for 100 times since a goes from 50 to 5000
    a=a+50;

[b,a]=ellip(1,20,25,[a 5000]/(fs/2),'bandpass');

% 2 
y2=audioread('2.mp3');
y_h2=filter(b,a,y2);
power2=rms(y_h2)^2;

% 3 
y3=audioread('3.mp3');
y_h3=filter(b,a,y3);
power3=rms(y_h3)^2;

%Power calculations
PowerN=((0.14*power2)+(0.14*power3))/2;

%%%%%%%%%%%
[x,fs]=audioread('fr1.mp3');
x_h=filter(b,a,x);
PowerW=rms(x_h)^2; %RMS formula

%%%%%%Figure of Merit%%%%%% 
   Total_power= PowerW/PowerN;
   disp(Total_power)

end

Please help! Thanks!

Answer 1

[Stephen23]

Look closely at the variable a:

a=0;
for ..
    a=a+50;
    [b,a]=ellip(..[a 5000]..);
    ..
end

At the start of the first iteration a = 0, to which you add 50. However you then completely replace that variable a with an entirely different one (the second output from ELLIP, which is a vector of transfer function coefficients of the filter).

After that it appears that you assume that a is still as scalar, whereas in fact you have replaced it with a vector.

[Giggs B.]

Oh wow, that was a silly mistake. It's orking fine now. Thank you so much!

[Giggs B.]

Yes, I changed the variable name and it is working as expected :)