curve fit

Posts: 64
Joined: 2015-03-18
Location: United States

Hello, I would like to fit two lines on the curve shown in attachment, however I don't know what function in Igor Curve fit to use. My x-axis is also a timewave, would that be an issue when doing a curve fit? Thanks!


Posts: 1815
Joined: 2007-06-29
Location: United States

In general, you would pick a fitting function based on the theory that you think explains the data. You say "two lines" and I presume you mean "two curves", and you are probably trying to fit the obvious segments from the left to the big jump with a cluster of green points, and then from the green points to the end.

Those curves appear to my eye to be basically exponential or possibly double exponential.

If the X values are date/time, then the X values are very large and exponentials will overflow. You would need to fit with exp_XOffset or dblexp_XOffset to avoid overflow.

Since you are fitting two segments of a single wave, you would need to re-name the waves created by the fit after the first fit to avoid having the first results overwritten by the second fit.

John Weeks
WaveMetrics, Inc.

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