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parameters problem in FindFit

• To: mathgroup at smc.vnet.net
• Subject: [mg92855] parameters problem in FindFit
• From: gyzhou at 139.com
• Date: Wed, 15 Oct 2008 05:37:53 -0400 (EDT)

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.

• Follow-Ups:
  • RE: parameters problem in FindFit
    • From: "Richard Hofler" <rhofler@bus.ucf.edu>