Re: Nonlinear Fit Problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg7285] Re: Nonlinear Fit Problem*From*: junkin <junkin at augustus0.physics.unc.edu>*Date*: Thu, 22 May 1997 09:19:31 -0400 (EDT)*Organization*: Duke University, Durham, NC, USA*Sender*: owner-wri-mathgroup at wolfram.com

I have included a simple example below just to demonstrate the problems that I have encountered with the NonlinearFit routine (in the Statistics'NonlinearFit' package). As you can clearly see, the addition of a constant gives an erronious fit. Is there a patch available, or is this a feature that I do not understand? I am using Mathmatica version 3.0.0.0. Thank you, David Junkin In[82]:= data7={{1,1},{2,2.1},{3,3.1},{4,4.3},{5,5.4}} datafit=NonlinearFit[data7, (a + 1) - 1/6 b x + 1/120 c x^2 ,{x}, {a,b,c}] datafit2=NonlinearFit[data7, a - 1/6 b x 1/120 c x^2 ,{x}, {a,b,c}] Out[82]= {{1,1},{2,2.1},{3,3.1},{4,4.3},{5,5.4}} Out[83]= 0.9800 + 1.014285 x + 0.01428 x^2 Out[84]= -0.01991.01428 x + 0.01428 x^2