RE: parameters problem in FindFit

*To*: mathgroup at smc.vnet.net*Subject*: [mg92864] RE: [mg92855] parameters problem in FindFit*From*: "Richard Hofler" <rhofler at bus.ucf.edu>*Date*: Thu, 16 Oct 2008 05:04:04 -0400 (EDT)*References*: <200810150937.FAA11790@smc.vnet.net>

Hi, You'll probably get many similar answers. The Mathematica Documentation Center says this: FindFit[data,{expr,cons},pars,vars] finds a best fit subject to the parameter constraints cons. So, add constraints to your function. In[5]:= FindFit[lis, {a - (b x^2)/(c + x), {1.13 < a < 1.15, .0001 < b < .0004, 299 < c < 301}}, {a, b, c}, x] Out[5]= {a -> 1.14624, b -> 0.00035099, c -> 299.942} I hope this helps. Richard Hofler -----Original Message----- From: gyzhou at 139.com [mailto:gyzhou at 139.com] Sent: Wednesday, October 15, 2008 5:38 AM To: mathgroup at smc.vnet.net Subject: [mg92864] [mg92855] parameters problem in FindFit Hi, guys : I get a list like this : lis = {{12.5, 1.146}, {32, 1.145}, {50, 1.144}, {69, 1.1424}, {84.6, 1.139}} My aim is : FindFit[lis, a - (b x^2)/(c + x), {{a, 1.14}, {b, 0.0003}, {c, 300}}, x] As we can see, I want this list to be fitted using parameters a, b, c around 1.14, 0.0003, 300. However Mathematica gives { b, 10^8} and {c, 10^14} far from what I expect.I set "MaxIterations" to less times, but it doesn' t make sense. My friends didn't give the answer either, I am here for your advice. Thanks in advance.

**References**:**parameters problem in FindFit***From:*gyzhou@139.com