How do I store values from inside a loop?

Question

Srikanth 2013-3-19

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/67748-how-do-i-store-values-from-inside-a-loop

In my program, I'm creating a Butterworth filter and making a couple of calculations (E1 and E2 in the code). I want to store the values of E1 and E2 into a file, and be able to identify the order (i in the code), and the cutoff frequency (w in the code) of a specific value later on. If I write them into an array or a matrix, I'm afraid I won't be able to identify the values. What should I do?

order = input('Enter max order of the filter: ')
Fsam = input('Enter sampling frequency in Hertz: ')
f = 0 : 0.01 : Fsam/2;        
for i = 1:order
    for w = 0.1:0.1:0.9
        [b,a] = butter(i,w);
        H = freqz(b,a,f,Fsam);
        fc = w * Fsam / 2;
        p = find(f == fc);
        PassBand = ones(1,p);
        I1 = PassBand - H(1:p);
        J1 = mean(I1);
        E1 = abs(J1);
        StopBand = zeros(1,length(f)-p);
        I2 = H(p+1:length(f)) - StopBand;
        J2 = mean(I2);
        E2 = abs(J2);
end
end

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Answer 1

Tobias 2013-3-19

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https://ww2.mathworks.cn/matlabcentral/answers/67748-how-do-i-store-values-from-inside-a-loop#answer_79171

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Firstly, I'll pass on an advice that I was once given here on the forum. You ought to use another letter in your loop than i, k for example. I believe this is because Matlab uses i and j for imaginary numbers, so just to safe yourself the mess, make it a habit to use another letter.

To fix your problem, you can assign variables as functions, which will store it in a vector / matrix. To do this, you should change your code to the following:

Notice especially the lines: 4, 6, 13 and 17

order = input('Enter max order of the filter: ')
Fsam = input('Enter sampling frequency in Hertz: ')
f = 0 : 0.01 : Fsam/2;        
for k = 1:order
    for w = 0.1:0.1:0.9
        [b,a] = butter(k,w);
        H = freqz(b,a,f,Fsam);
        fc = w * Fsam / 2;
        p = find(f == fc);
        PassBand = ones(1,p);
        I1 = PassBand - H(1:p);
        J1 = mean(I1);
        E1(k) = abs(J1);
        StopBand = zeros(1,length(f)-p);
        I2 = H(p+1:length(f)) - StopBand;
        J2 = mean(I2);
        E2(k) = abs(J2);
end
end