I am trying to find the valley in a sequence of numbers of around 2000 length. It is a plot of the sequence of numbers

Always prominently there will be two peaks. But the value and location might change. I need to find the valley, defined as the lowest point between the two peak values.

I tried using the following code:

% sums = list of positive integers generated from an analysis
inverted_sums = double(max(sums) - sums); % inverting the sequnce
[~,locs] = findpeaks(inverted_sums) % finding the peaks

But the above code returns many valleys with even a small difference, including the correct one. How do I solve it?


The following code will find the lowest point between two prominent peaks.

%Smoothing the data
movAvgFiltOrder = 8;
b = filter(ones(1,movAvgFiltOrder)/movAvgFiltOrder,1,sums); 

% finding peaks from the smoothed curve
[vals,pos] = findpeaks(b);
idx = find(vals>mean([min(vals),max(vals)])); % removing peaks which are below the average, 
%this is helpfull if some lower amplitude peaks are caught at sides of the prominent peaks.

peak_pos1 = pos(idx(1)); % farthest prominent peak on one side of valley
peak_pos2 = pos(idx(end)); % farthest prominent peak on other side of valley

% correcting the peak positions for filter delay (Coarse tuning)
peak_pos1 = peak_pos1 -  movAvgFiltOrder/2;
peak_pos2 = peak_pos2 -  movAvgFiltOrder/2;

% Looking for any other peaks nearby (Fine Tuning)
tuning_range = min(movAvgFiltOrder,floor(abs((peak_pos2-peak_pos1-1)/2)));
p1 = peak_pos1-tuning_range:peak_pos1+tuning_range;
p2 = peak_pos2-tuning_range:peak_pos2+tuning_range;
[~,r1] = max(sums(p1));
[~,r2] = max(sums(p2));
peak_pos1 = p1(r1);
peak_pos2 = p2(r2);

% Identifying valley
valley = sums(peak_pos1:peak_pos2);

% finding minimum point in valley
[min_val,pos_min_val] = min(valley);
valley_amplitude = min_val; % amplitude of minimum point
valley_position  = peak_pos1+pos_min_val-1; % finding the valley point in the entire array

This valley_position will give the poisition of the lowest point between major peaks.

  • $\begingroup$ It worked very beautifully for me.. Thank you.. please replace the 'a' with 'sums' in valley = a(peak_pos1:peak_pos2); $\endgroup$
    – Prashant
    Jun 9 '18 at 5:03
  • $\begingroup$ Hi @prashanth.. if you found answer useful, please upvote the answer. $\endgroup$
    – srk_cb
    Jun 10 '18 at 1:37

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