find x intercepts numerically

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Elizabeth Ramsey
Elizabeth Ramsey 2020-5-25
评论： Elizabeth Ramsey 2020-5-25
I'm trying to find a quick way of returning the index of all the places where an [x,y] data set crosses the x axis.
I've tried: zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0)
But it isn't returning all the zeros and also always returns the last value in my dataset as a zero even though it isn't. I'm testing with a third order polynomial and can only get my code to work if it have only one root.
Thanks!

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Ameer Hamza
Ameer Hamza 2020-5-25
编辑：Ameer Hamza 2020-5-25
Try this
f = @(x) find(diff(sign(x)));
Example
>> x = [1 2 -1 -2 -1 2 3 1 -2 -3 -2 1];
>> f(x)
ans =
2 5 8 11

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