In MATLAB, find zero crossings within a threshold, given a vector of data

问题

I have written a function in MATLAB to count the number of zero crossings given a vector of signal data. If I find a zero crossing, I also check whether the absolute difference between the two vector indices involved is greater than a threshold value - this is to try to reduce the influence of signal noise.

    zc = [];
    thresh = 2;
    for i = 1:length(v)-1
        if ( (v(i)>0 && v(i+1)<0) || (v(i)<0 && v(i+1)>0) ) && abs(v(i)-v(i+1)) >= thresh
            zc = [zc; i+1];
        end
    end
    zcCount = length(zc);

I used the vector from the zero crossings function here to test it: http://hips.seas.harvard.edu/content/count-zero-crossings-matlab

    A = [-0.49840598306643,
         1.04975509964655,
        -1.67055867973620,
        -2.01437026154355,
         0.98661592496732,
        -0.06048256273708,
         1.19294080740269,
         2.68558025885591,
         0.85373360483580,
         1.00554850567375];

It seems to work fine but is there a more efficient way of achieving the same result? E.g. on the above webpage, they simply use the following line to calculate zero crossings:

    z=find(diff(v>0)~=0)+1;

Is there a way to incorporate the threshold check into something similarly efficient?

回答1:

How about

zeroCrossIndex=diff(v>0)~=0
threshholdIndex = diff(v) >= thresh;
zcCount = sum(zeroCrossIndex & threshholdIndex)

来源：https://stackoverflow.com/questions/37544446/in-matlab-find-zero-crossings-within-a-threshold-given-a-vector-of-data