Re: Finding peaks/max in a graph

[David Bateman]

According to edA-qa mort-ora-y <address@hidden> (on 04/05/04):
> David Bateman wrote:
> >A for-loop is not the way to go about this. Consider the code fragment
> >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.

Bzzzzzzz wrong....

octave:1> a = [1 2 3 4 5 4 3 2 1 2 3 2 1]';
octave:2> n = length(a);
octave:3> peaks = find([a(2:n,1) - a(1:n-1,1) < 0; 1] & [1; a(1:n-1,1) - 
a(2:n,1) <0])
peaks =

   5
  11

octave:4> a(peaks)
ans =

  5
  3

D.

-- 
David Bateman                                address@hidden
Motorola CRM                                 +33 1 69 35 48 04 (Ph) 
Parc Les Algorithmes, Commune de St Aubin    +33 1 69 35 77 01 (Fax) 
91193 Gif-Sur-Yvette FRANCE

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