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From: "Linus Utopia" <linus_utopia@gmail.com>
Newsgroups: comp.soft-sys.matlab,sci.math,sci.stat.math,sci.stat.consult,sci.stat.edu
Subject: Re: How to detect turning points in curves...
Date: Thu, 12 Jul 2007 21:31:04 -0400
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Hi all,

Please be advised that my curves are not continuous -- they are discrete 
data points. When I plotted them in Matlab, they are connected and looked 
like a continous curve. So I am not sure if the second "finite difference" 
will help..., and accurately...

> How to detect turning points in curves
>
> Hi all,
>
> If you take a look at the following plot,
>
> http://img63.imageshack.us/img63/5050/gggyt1.jpg
>
> You will agree with me that there are two turning points.
>
> But is there a systematic way to let computer detect the turning points 
> automatically and programmatically?
>
> Please be advised that the second turn isn't neccessarily turning down, it 
> can also possibly go up...
>
> And in real-world applications, the turn can be more smooth and round, but 
> still, naked eyes should be able to find the turning points easily.
>
> My program has to do a classification:
>
> All the good curves should first go down, and then either make no turns; 
> or make a turn, and stay vertically flat and slightly up, going from the 
> left to the right.
>
> There should be no second turn (up or down). If there is the second turn, 
> then that's the bad curves.
>
> My program needs to decern the good curves from bad curves.
>
> I cranked a few algorithms but they don't work well. Are there systematic 
> methods of handling this?
>
> Thanks a lot!
>
>
>
>
>
>