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Find the linear portion of a curve 
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#1
Jul1911, 02:30 PM

P: 363

Hi,
So I have a set of experimental data and I would like to find the slope of the linear portion of the data. For example, say I have set of points, the first few points are not linear, then there is a chunk of data in the middle that is linear, and then the last several points are very nonlinear. I would like to find the slope of this linear portion in the middle but the location and length of the linear portion will be different for each experiment. I could easily do this by just manually removing the nonlinear portions of the curve but I would like for the computer to be able to do this automatically. Does anyone have any suggestions on the best way to do this? Thanks 


#2
Jul1911, 04:08 PM

HW Helper
P: 925

Tricky business I would think. What the human brain can easily do isn't necessarily so easy to replicate with a computer program.
http://ieeexplore.ieee.org/stamp/sta...umber=05716374 http://en.wikipedia.org/wiki/Robust_regression http://www.mendeley.com/research/emp...relimination/ http://pubs.acs.org/doi/abs/10.1021/ed082p1472.2 


#3
Jul1911, 08:01 PM

P: 4,663

Will the curve fitting program mentioned in post #8 in http://www.physicsforums.com/showthread.php?t=364600 work?
Diffferentiate the result for the slope. Bob S 


#4
Jul2111, 09:07 AM

P: 536

Find the linear portion of a curve
You calculate the derivative for every points you have. This will give you the slope for every point. If the slope is the same as the next one, then you have a straight line between those 2 points. Any place where you have a straight line, the second derivative will be equal to zero (which means «no change in slope»).



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