# How can i know the abscissa of the maximum of a curve ?

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Mallouli Marwa le 20 Oct 2016
Hi
I have a curve Amplitude=f(frequency) and i want to know the abscissa of the maximum.
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Isn't the abscissa just the y-axis value of your function - i.e. Amplitude?
So just run your function and call
max( Amplitiude )
on the result.
John D'Errico le 20 Oct 2016
https://en.wikipedia.org/wiki/Abscissa
The y axis is the ordinate, not the abscissa.

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### Réponses (1)

John D'Errico le 20 Oct 2016
So you have a function of a single variable, and you need to know the location of the min.
If you have the function itself, then use fminbnd.
If you have only data points, thus (x,y) pairs, then use min. It returns the index of the minimum value(look at the second output argument), then use that index on the vector of x values.
If you want to find a minimum on data points, but you need an interpolated minimum, then you can use fminbnd on a spline fit. Don't expect it to be very good though.
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