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How can I get a matrix B of the indexes in a matrix A that satisfy the following —i representing index— A(i-1)>0 && A(i+1)<0?
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How can I get a matrix B of the indexes in a matrix A that satisfy the following —i representing index— A(i-1)>0 && A(i+1)<0?
Im ploting an oscillating graph, and would like to get indexes of rate of change closest to 0, in order to get the frequency.
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Star Strider
on 24 Dec 2017
‘Im ploting an oscillating graph, and would like to get indexes of rate of change closest to 0, in order to get the frequency.’
If you want to find the indices of the zero-crossings of your data, this little utility function could help:
zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0); % Returns Approximate Zero-Crossing Indices Of Argument Vector
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Roger Stafford
on 25 Dec 2017
B = find(A(1:end-2)>0 & 0>A(3:end)) + 1;
Note that the "+1" is necessary here. For example. if A(1)>0 and A(3)<0, we would want to get an index of 2 included in B, but without the "+1" 'find' would record it as an index of 1.
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