How to make sinewives with array input and for-loop?

if true
  % code
function output = analog_filter1(input)
%
% Simulated analog filter used in Problem 1.3
%
Ts = .001;
N = 1000;
t = (0:999)*Ts;
make_an_array = [2 10 15 20 30 40 50 60 80 90 100 150 200 300 400];
f = make_an_array;
for i=1:length(t)                              
input(i)=sin(2*pi*f(1)*t(i));     
end  
[b,a] = butter(4,.02,'High');
[b1,a1] = butter(2,0.12);
input = filter(b1,a1,input);
output = filter(b,a,input);
for i=1:length(output)                              
G(i) = 20*log(output/f(1));  
end 
semilogx(f,G,'x')
xlabel('frequency in Hz')
ylabel('Gain dB')
A = max(output);
grid on
disp(A)
end

This is a brief explaination about what I am trying to find: 1. Amplitude of the output with max operator (variable A) 2. Sine wives using input frequencies in an array (variable f) and use a for-loop (input (i)) 3. Plot the 20 log of the output values against the frequency array using the semilogx. 4. I dont know about how to 'store the maximum values of the flter’s output in an array for plotting'. And then, I got error message "Subscripted assignment dimension mismatch."

Answer 1

[Himanshu]

Hi Venya,

Here is a revised version of your code.

function output = analog_filter1()
    % Simulated analog filter used in Problem 1.3
    Ts = 0.001;
    N = 1000;
    t = (0:N-1) * Ts;
    make_an_array = [2 10 15 20 30 40 50 60 80 90 100 150 200 300 400];
    f = make_an_array;
    max_values = zeros(1, length(f)); % Array to store maximum values

    for i = 1:length(f)
        input = sin(2 * pi * f(i) * t); % Generate sine wave for each frequency
        [b, a] = butter(4, 0.02, 'high');
        [b1, a1] = butter(2, 0.12);
        input = filter(b1, a1, input);
        output = filter(b, a, input);
        max_values(i) = max(output); % Store the maximum value of the output
    end

    G = 20 * log10(max_values); % Calculate 20 log of the maximum values
    semilogx(f, G, 'x');
    xlabel('Frequency in Hz');
    ylabel('Gain (dB)');
    grid on;
    disp(max_values); % Display the maximum values
end

Key Changes:

1. The input parameter has been reomved and the function now generates the input internally.
2. Generate sine waves for each frequency in the array with the help of a loop.
3. Use an array max_values to store the maximum output values for each frequency.
4. Calculate the 20 log of the maximum values and plot them using semilogx.

Explanation:

1. For each frequency in the array f, a sine wave is generated.
2. The sine wave is filtered using two Butterworth filters.
3. The maximum value of the filtered output is stored in the max_values array.
4. The 20 log of the maximum values is plotted against the frequency array using semilogx.

I have confirmed on my end that the above changed resolve the “Subscripted assignment dimension mismatch” error and correctly plot the desired graph.