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POpeaks and troughs in MATLAB (but with corresponding definition of a peak and trough)
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copied!<p>I want to look for peaks and troughs in a given vector of data, with the following definition.</p> <p>A "peak" is a local maximum at least x% higher than the preceding trough, and a "trough" is a local minimum at least x% lower than the preceding peak. x here is referred to as a cutoff. In the paper I am writing, the cutoff is referred to as the standard deviation of the data.</p> <p>I thought of writing a function that enables me to find a peak and a trough. The function that I wrote was this. I will call this from the main data.</p> <pre><code>function [vectpeak,vecttrough]=peaktrough(cutoff,x,lastobs,t) % This function gives you two outputs: a vector of ones and zeros that locate PEAKS and % a vector of ones and zeros that locate TROUGHS. % To be able to get a vector of peaks and troughs, we have to give % four inputs. % CUTOFF: This is what Chang and Osler [1999] use to identify if a data % point is a peak or a trough. A PEAK is defined as "a local maximum that is % x percent higher than the preceding trough." (Chang and Osler, 1999) % and a TROUGH is defined as "a local minimum that is x percent lower % than the preceding peak." This is a scalar. % VECTOR: This is the vector of data that will be used for the purposes of % the identification. % LASTOBS: This is the last observation of the data. % t: This specifies the time. % Pre-allocations. vectpeak=zeros(lastobs,1); % This is the vector of peaks. vecttrough=zeros(lastobs,1); % This is the vector of troughs. % Computing for the troughid's and peakid's. temptroughid=troughid(cutoff,x,lastobs,t); temppeakid=peakid(cutoff,x,lastobs,t); % Determining whether a function is a peak or a trough. while t<lastobs t=t+1; if x(t)>=temptroughid(t); vecttrough(t)=1; vectpeak(t)=0; maximum=x(t); elseif x(t)<=temppeakid(t); vecttrough(t)=0; vectpeak(t)=1; minimum=x(t); else vecttrough(t)=0; vectpeak(t)=0; end end function findtrough=troughid(cutoff,y,lastobs,t) % This function computes for the TROUGHID which will be used in % determining whether we have a trough or a peak. % Initializations. findtrough=zeros(lastobs,1); tempmin=zeros(lastobs,1); minimum=y(1); % This is how the function works. while t<lastobs; t=t+1; if y(t)<minimum; tempmin(t)=y(t); minimum=y(t); else tempmin(t)=minimum; end findtrough(t)=tempmin(t)*(1+cutoff); end end function findpeak=peakid(cutoff,y,lastobs,t) % This function computes for the PEAKID which will be used in % determining whether we have a peak. % Initializations. findpeak=zeros(lastobs,1); tempmax=zeros(lastobs,1); maximum=y(1); % This is how the function works. while t<lastobs; t=t+1; if y(t)>maximum; tempmax(t)=y(t); maximum=y(t); else tempmax(t)=maximum; end findpeak(t)=tempmax(t)*(1-cutoff); end end end </code></pre> <p>The problem that I am getting is that I am getting weird results. For instance, I get a vector where all are peaks, and none are troughs, which does not make sense, since if I use the <code>findpeaks</code> command of MATLAB, I am able to identify peaks and troughs, and they are not successive. </p> <p>Is there a way where I could tweak my code, or if not, to use findpeaks or its algorithm to find the peaks and troughs based on my definition? </p>

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