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MathGroup Archive 1995

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Re: Switch Axis?

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg1073] Re: Switch Axis?
  • From: rubin at msu.edu (Paul A. Rubin)
  • Date: Fri, 12 May 1995 17:21:00 -0400
  • Organization: Michigan State University

In article <3ohk87$5k2 at news0.cybernetics.net>,
   chris at canada.medchem.purdue.edu (chris) wrote:
[snip]
->I was also trying to do nonlinearfitting to the following group of data: 
->{0.5, 0.001}, {0.15, 0.005}, {0.1, 0.01}, {0.01, 0.1}, {0.001, 0.5}
->The function
->         1-1/(1+0.00065/x) 
->produces a curve (use LogPlot[1-1/(1+0.00065/x), {x, 0.001,1 }) that 
seems
->to fit the data. However, when I used NonLinearFit with this function, I
->got the message that the function does not match a real number when
->x=0.001.
->Could someone help me on these two problems? Thanks a lot!

I would guess you had a syntax error.  NonlinearFit worked ok when I used 
models with either one or two coefficients to be fitted (you didn't specify 
which coefficients were symbolic in your model):

  data = {{0.5,0.001}, {0.15, 0.005}, {0.1, 0.1}, 
          {0.01, 0.1}, {0.001, 0.5}};
  NonlinearFit[ data, 1-1/(a+b/x), x, {a, b} ]  (* fit two coeffs *)
       {a -> 1.02788, b -> 0.000938836}
  NonlinearFit[ data, 1-1/(1+b/x), x, {b} ]     (* fit one coeff *)
       {b -> 0.000981788}

Paul

**************************************************************************
* Paul A. Rubin                                  Phone: (517) 432-3509   *
* Department of Management                       Fax:   (517) 432-1111   *
* Eli Broad Graduate School of Management        Net:   RUBIN at MSU.EDU    *
* Michigan State University                                              *
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Mathematicians are like Frenchmen:  whenever you say something to them,
they translate it into their own language, and at once it is something
entirely different.                                    J. W. v. GOETHE


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