zero crossing and inflection point

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Osita Onyejekwe 2016-11-1

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https://ww2.mathworks.cn/matlabcentral/answers/310148-zero-crossing-and-inflection-point

回答： John D'Errico 2016-11-1

can someone please in detail explain to me what this simple line of coding is doing in order to calculate zero crossing. I thought you needed the second derivative of the function to do this. Thank you

zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0);

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Answer 1

John D'Errico 2016-11-1

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Why would you possibly need the second derivative to locate a zero crossing?

All this does is look for consecutive elements of a vector that have different signs.

If you really want to see what it does, read the help for circshift. My re-writing existing help will be a waste of time. Given that, what property do two numbers have if they have different signs? Answer: the product will ALWAYS be negative. So all that line does is look for consecutive elements with opposite signs. (Zero will do too.)