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MathGroup Archive 2002

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HELP! Strange evaluations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33578] HELP! Strange evaluations
  • From: "Lawrence A. Walker Jr." <lwalker701_remove_ at earthlink.net>
  • Date: Mon, 1 Apr 2002 02:02:12 -0500 (EST)
  • Organization: Morgan State University, COMSARE
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

For the life of me I can't figure out how to get the following to work 
correctly.  I also tried using various combinations of Hold and Evaluate 
-- but to no avail.

<< Statistics`NonlinearFit`

(* This works ok *)
goo[a_, b_] :=
   FindRoot[( Cos[a x]) == b x, {x, 0}][[1, 2]];

(* Here are some sample data *)
data = Table[{i, goo[i, .5]}, {i, 0, 1, .2}];

(* This doesn't work -- I expect b->.5 to be returned. *)
BestFitParameters /.
   NonlinearRegress[data, goo[a, b], a, {b, {0., 1.}},
      RegressionReport -> BestFitParameters]


After executing the above, I get the following error messages:

FindRoot::frnum: Function {0. b+Cos[0. a]} is not a length 1 list of 
numbers at {x} = {0.}.

NonlinearRegress::nonnum: The model is not numerical at {b->0., a->0.}. 
  Check that all model parameters are included in the parameter list...

How do I get the above to work.


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