MATLAB: How to ensure two vectors are the same size when using findpeaks

findpeakslocal maximalocal minimaMATLABpeak to peakresize vector

I am using findpeaks to determine the local minima and maxima in a given input signal. I am then calculating the peak-to-peak difference between each of these minima/maxima pairs throughout the entire signal. Shown is my current code:
signal = myvector;
[pksmax,locsmax] = findpeaks(signal);
[pksmin,locsmin] = findpeaks(-signal);
 
realpksmin = -1*pksmin;
for j = 1:size(realpksmin)
    pk2pkmaxmin(j) = abs(pksmax(j) - realpksmin(j));
end
Most of the time, 
size(pksmax) == size(pksmin)
Sometimes these two vectors differ in size very slightly. If the above statement is false, then I have an error in my loop, 
Index exceeds the number of array elements (154).
How can I ensure that 
size(pksmax) == size(pksmin)
is always true upon using findpeaks(signal)?

Best Answer

  • The number of local maxima and minima need not be same for every signal so you can’t get size of both the arrays same every time. A possible solution is to use array slicing and reduce the size of the large array to smaller one. Refer to the code below,
    commonLength = min(length(pksmax) , length(pksmin));
    pksmax_new = pksmax(1:commonLength);
    pksmin_new = pksmin(1:commonLength);
    Alternatively you can also insert zeros to the shorter array so that it’s length becomes equal to the longer one.
    • Related Question