Message: 26
Date: Sat, 04 Dec 2010 12:56:05 -0500
From: Bryan McCormick <br...@deepfoo.com>
To: use-livecode@lists.runrev.com
Subject: Finding local minima and maxima of a graph
Message-ID: <4cfa80b5.3090...@deepfoo.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I have a very large number of graphs to crunch through to find local
minima and maxima. The data is regularly spaced, which eliminated one
problem. I know too that the window value used has to be an adjustable
variable as peak and trough significance may need to be found for a
wide
range of time periods within the data set.
I had thought of using a moving average to find a slope of zero and
then
use an offset function to find the peak and trough in time.
I've used stackoverflow to have a look and apparently the problem is a
lot less trivial than I thought.
Any suggestions for fitting to a function, using the graphing
functions
in rev, etc would be most welcome.
Bryan,
If the data is "well behaved" you might try just finding out where the
derivative (slope) changes sign. For example:
function MinMax tList
put line 1 of tList into yOld
put 0 into dyOld
repeat for each line yNew in tList
put yNew - yOld into dy
put dy * dyOld into tChange
if tChange < 0 or tChange = 0 then
put yNew & cr after tExreema
end if
put ynew into yOld
put dy into dyOld
end repeat
return tExreema
end MinMax
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