How do I find a max value of a signal defined within a range?

Hello, so I have a signal with several peaks, but I am only looking for a max peak within a specific range of that signal. So instead of getting the max peak, I want the max value within a specific range of that signal.

This is the code I am using right now to find the max peak of the signal:

if true
  s = signal;
  max = find(max(s) == s);
end

The key is that I still am looking for a max value of the signal 's', but only within a range of 12 to 15 seconds of that signal.

Any help would be greatly appreciated. Thank you for taking the time to look at my problem.

Answer 1

[Image Analyst]

To find the max of the signal and what element it occurs at, you can do this:

[maxSignal, indexOfMax] = max(signal)

I don't know how many elements correspond to 12 to 15 seconds, but let's just assume here that it is 100 elements. So you can do

index1 = indexOfMax - 100;
if index1 < 1
    index1 = 1; % Don't allow negative or zero indexes.
end
index2 = indexOfMax + 100;
if index2 > length(signal)
    index2 = length(signal); % Don't allow negative or zero indexes.
end

Now you want the max in the range from index1 to index2 but obviously not the first max you found. So you can set the array before index1, and after index2, and at the first max to minus infinity. Then call max again. This will find " max value of the signal 's', but only within a range of 12 to 15 seconds" of the first max as you asked for

signal(1:index1) = -inf;  % Make a copy of signal if you want to save the original.
signal(index2:end) = -inf;
signal(indexOfMax) = -inf;
[secondMax, indexOfSecondMax] = max(signal);

An alternate method is to sort the signal but then you have to check the sorted values to see if their indexes are within 12-15 seconds of the first index.

[sortedValues, sortIndices] = sort(signal, 'descend');
maxSignal = sortedValues(1);
indexOfMax = sortIndices(1);
% Now find second, but has to be within, say, 100 elements
k = 2;
while k < length(sortIndices)
    indexesApart = sortIndices(k) - sortIndices(1);
    if abs(indexesApart) < 100
        break;
    end
    % If we get here, it's not within 12-15 seconds of the first max.
    % So increment the index and try again.
    k = k +1;
end
% Get the actual index
indexOfSecondMax = sortIndices(k)
% Get the signal value at that location.
secondMax = signal(indexOfSecondMax)

[Anonymous45]

I am not sure if I was clear enough with my explanation of what I am looking for, so let me give you more detail. I hope this doesn't make it more complained.

So this is exactly what I am trying to do I have two signals. I am taking the max peak of signal 1 ('s1') which is 3.019 Hz and then to create a range I am subtracting .05 and adding .05 to 3.019 to create a range of 2.969 Hz to 3.069 Hz. Then I want to use that range to find signal 2's peak between 2.969 Hz to 3.069 Hz. Therefore I do not truly know the number of elements within that range, I just want to find the peak for signal 2 within that range.

if true
signal = cos(2*pi*f*t).*(A.*(heaviside(t)-heaviside(t-39E-9)));
data1 = zeros(1000,1);
index1 = 0;
%Graphed signal_4
signal_4 = [cos(2*pi*f*t).*(A4.*(heaviside(t)-heaviside(t-4E-9)))]+[cos(2*pi*f*t).*(A4.*(heaviside(t-7E-9)-heaviside(t-11E-9)))];
data4 = zeros(1000,1);
index4 = 0;
      snrdB = 0;
      noise = 10^(-snrdB/20)*randn(size(signal));
      sn = noise+signal;
      y1 = fft(sn,nfft);
      m1 = abs(y1);
      er1 = (0:length(y1)-1)*(1/h)/length(y1); 
      indexmax1 = find(max(m1) == m1);
      xmax1 = er1(indexmax1);
      ymax1 = m1(indexmax1);
      index1 = index1 + 1;
      data1(index1, 1:1) = xmax1(1,1);
%Graphed signal_4
      snrdB = 0;
      noise4 = 10^(-snrdB/20)*randn(size(signal_4));
      s4n = noise4+signal_4;
      y4 = fft(s4n,nfft);
      m4 = abs(y4);
      er4 = (0:length(y4)-1)*(1/h)/length(y4);
      indexmax4 = find(max(m4) == m4);
      xmax4 = er4(indexmax4);
      ymax4 = m4(indexmax4);
      index4 = index4 + 1;
      data4(index4, 1:1) = xmax4(1,1);

end

[Image Analyst]

I'm not sure I understand. First of all, it looks like signal is a time domain signal. You have not defined your t axis or the frequency. But the frequency looks like a single number, not a range. I can't even run your code because you have not defined t and f.

http://www.mathworks.com/matlabcentral/answers/13205#answer_18099

http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

[Anonymous45]

I was trying not to give away to much of my code mostly just the skeleton of it with hopes that someone can just help me define a range and find a peak within that range. The signal is Fourier Transformed into frequency domain.