Problem with for loop

Question

Srikanth 2013-3-19

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/67782-problem-with-for-loop

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

My program can be broken into four parts:

1. Starting loop - asks the user what kind of filter (and window, if necessary) they want

2. work() - calculates 2 errors, and writes them onto a .txt file on disk.

3. createFilter() - creates the necessary filter, and return the vectors b and a

4. toWriteErrors() - creates a .txt file on disk to write the values of E1 and E2 to.

The main problem is in work(). The second for loop, the one that iterates 'w' from 0.1 to 0.9, is not producing values for the THIRD and SEVENTH iterations. Everywhere else it works fine. Just for those two iterations, it gives the values of E1 and E2 (the errors I am calculating) as NaN. I have no clue what is causing this. What do I do?

1. STARTING LOOP

while true
    n = input('Enter the type of filter; 0 = IIR, 1 = FIR: ')
    if n == 0
        %IIR Create
        expr = 'IIR';
        expr
        work(expr)
        break
    elseif n == 1
        %FIR Create
        type = input('Enter the windowing technique; \n0 = boxcar, 1 = hamming, 2 = hanning, 3 = kaiser: ')
        if type == 0
            %Boxcar create
            expr = 'FIR Boxcar';
            expr
            work(expr)
            break
        elseif type == 1
            %Hamming create
            expr = 'FIR Hamming';
            expr
            work(expr)
            break
        elseif type == 2
            %Hanning create
            expr = 'FIR Hanning';
            expr
            work(expr)
            break
        else
            %Kaiser create
            expr = 'FIR Kaiser';
            expr
            work(expr)
            break
        end
    else
        disp 'Unrecognized command. Please enter either 0 or 1'
    end
end

2. work()

%The Problematic function. Calculates values for E1 & E2, and writes them to disk  
function work(expr)
fid = toWriteErrors(expr);
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 %The problematic loop. 3rd & 7th iterations not working
        [b,a] = createFilter(expr,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 = 0;
        E1 = abs(J1); %First error
        fprintf(fid,'E1_%s_%s = %.4f\n',int2str(k),num2str(w,'%.1f'),E1);
        StopBand = zeros(1,length(f)-p);
        I2 = H(p+1:length(f)) - StopBand;
        J2 = mean(I2);
        E2 = 0;
        E2 = abs(J2); %Second error
        fprintf(fid,'E2_%s_%s = %.4f\n',int2str(k),num2str(w,'%.1f'),E2);
    end
end
fclose(fid);

3. createFilter()

%Create filters
function [b,a] = createFilter(expr,i,w)
switch expr
    case 'IIR'
        [b,a] = butter(i,w);
    case 'FIR Boxcar'
        b = fir1(i,w,boxcar(i+1));
        a = 1;
    case 'FIR Hamming'
        b = fir1(i,w);
        a = 1;
    case 'FIR Hanning'
        b = fir1(i,w,hanning(i+1));
        a = 1;
    case 'FIR Kaiser'
        b = fir1(i,w,kaiser(i+1));
        a = 1;
end

4. toWriteErrors()

    %Create filenames for .txt files for different filters
  function fid = toWriteErrors(expr)
  switch expr
      case 'IIR'
          filename = 'errors_iir.txt';
      case 'FIR Boxcar'
          filename = 'errors_boxcar.txt';
      case 'FIR Hamming'
          filename = 'errors_hamming.txt';
      case 'FIR Hanning'
          filename = 'errors_hanning.txt';
      case 'FIR Kaiser'
          filename = 'errors_kaiser.txt';
  end
  fid = fopen(filename,'w');

2 个评论
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Jan 2013-3-19

What does "3rd & 7th iterations not working" exactly mean? As long as we only see the failing code, how could we suggest an improvement wiuthout using a crystal ball?

Srikanth 2013-3-19

Oops. I thought I'd explained it properly. Okay here goes. I'm trying to calculate E1 and E2, basically. In the for loop that I marked with that comment, the values for all iterations except the 3rd and 7th are working just fine. That is, they're producing values (or numbers) for E1 and E2. But the 3rd (w = 0.3) and 7th (w = 0.7) were outputting "E1 = NaN, and E2 = NaN". And I couldn't figure out why those two iterations were so cruel to me. It turns out its because the values 0.3 and 0.7 are actually approximated, not precise. Well, thanks to a Mr. Walter Roberson, its all good now.

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