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How can I find the position of a real number in a vector?

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Cantor Set
Cantor Set on 5 Mar 2020
Edited: James Tursa on 5 Mar 2020
I have a vector v:
v=[-0.9990;0.8988;2;3];
I want to find the position of -0.9990.
I used find(x==-0.9990) it does not work.
Any solutions?
Thanks

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Accepted Answer

James Tursa
James Tursa on 5 Mar 2020
Edited: James Tursa on 5 Mar 2020
Welcome to the world of floating point arithmetic. The number you are searching for cannot be represented exactly in IEEE double precision, so calculations involving it are subject to roundoff errors.
You will need to do the search with some tolerance. E.g.,
find( abs(x - (-0.9990)) < 1e-10 )
P.S. Your example actually does work if you use "v" instead of "x". I am assuming your actual v is built differently. Or maybe the typo is the entire problem.

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