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MathGroup Archive 2004

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NonlinearFit works not so good

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49566] NonlinearFit works not so good
  • From: Daohua Song <ds2081 at columbia.edu>
  • Date: Fri, 23 Jul 2004 06:00:40 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Dear group,
      I find the NonlinearFit give an answer far away from the truth; Here 
is an example:
     Plot[100 Sin[3 x+1]+2,{x,0,5}];
data=Cases[Graphics[%],Line[x___]?x,Infinity];
<<Statistics`NonlinearFit`
NonlinearFit[data//First,A Sin[B x+C]+D,{x},{A,B,C,D}];
Plot[%,{x,0,5}]
ListPlot[data//First]

     If i chop the +2 from above, it works fine. but The whole thing gives 
bad fit again if you change {x,0,5}->{x,0,10}
     So NonlinearFit also is not stable!
     I hope it should be improved
Daohua


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