how do I use a polynomial formula to extrapolate data?

jmckeone

Well-known Member
Joined
Jun 3, 2006
Messages
550
I've been able to use linear trendline formulas to extrapolate future data without an issue. In a y=mx+b scenario where y is the usage level and x is the date. However when I try to do something similar with a polynomial formula such as y = 1E-254x^56.468 the math goes to pot. Can anyone help?
 

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hatman

Well-known Member
Joined
Apr 8, 2005
Messages
2,664
That's the nature of Polynomial trendlines: they tend to diverge quickly once you move outside the data set: good for interpolation, not so good for extrapolation. What often happens in these cases is that the best fit polynomial uses a much larger exponent than the ideal curve that should approximate the data. You've got to jump pretty deep into advanced number theory to get a better prediction.
 

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