findextrema.m

Finds minima and maxima of data.

Description

FINDEXTREMA - finds minima and maxima of data
 
  If 'y' is the data the function finds the maximas 'ma' and minimas 'mi'.
  The x-position of the extrema are interpolated.
 
  Usage: [ma,mi]=findextrema(y);
 
  Example:
     x=-10:0.1:10; y=sin(x);
     [ma,mi]=findextrema(y);
     plot(y); hold on; plot(ma,y(round(ma)),'ro'); plot(mi,y(round(mi)),'gs'); hold off;

• MATLAB release: MATLAB 6.0 (R12)

[Jerry Wolf]

This looks like a very useful function, and the feature of interpolated x-positions is cute. Unfortunately, in the 2nd case I tried it on, I found that it misses some extrema and misplaces others. See this example:

y=[-196.7906 -188.8165 -196.5088 -193.5867 -194.6516 -190.3382...
-186.7008 -199.9656 -192.8946 -187.4440 -186.5194 -183.2169...
-201.4095 -198.7111 -189.9841 -195.6190 -189.6214 -188.5710...
-190.1472 -197.9514 -185.7049];
[ma,mi]=findextrema(y);
figure; plot(y); hold on; plot(ma,y(round(ma)),'ro');plot(mi,y(round(mi)),'gs'); hold off

[robert haberman]

This doesn't work for data exhibiting numerous strong maxima and minima.