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## Re: Finding peaks/max in a graph

 From: Joe Koski Subject: Re: Finding peaks/max in a graph Date: Mon, 05 Apr 2004 09:56:49 -0600 User-agent: Microsoft-Entourage/10.1.4.030702.0

```on 4/5/04 9:22 AM, edA-qa mort-ora-y at address@hidden wrote:

> David Bateman wrote:
>> n = 9
>> a = [1 2 3 4 5 4 3 2 1]';
>> peaks = find([a(2:n,1) - a(1:n-1,1) < 0; 1] & [1; a(1:n-1,1) - a(2:n,1) <
>> 0]);
>> that will find all indexes of the peaks in the data in a single statement
>
> If you set
>  a = [1 2 3 4 5 4 3 2 1 2 3 2 1]';
> Peaks will only find 5, not the 3 as well.  I will see if somehow,
> however, I can modify my code not to use a for-loop, rather to use a
> similar notation to above.

Another routine called extr.m that calculates both extrema and zero
crossings is at

http://perso.ens-lyon.fr/patrick.flandrin/emd.html

That routine is part of a package based on the Empirical Mode Decomposition
approach that does, in my opinion, a much better job of finding frequency
content of a signal than the classical fft approach. The fft assumes that
signals are strictly periodic and stationary, EMD does not.

Joe Koski

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