Re: NonlinearModelFit and assumptions on fit parameters
- To: mathgroup at smc.vnet.net
- Subject: [mg128206] Re: NonlinearModelFit and assumptions on fit parameters
- From: Frank K <fkampas at gmail.com>
- Date: Mon, 24 Sep 2012 00:32:49 -0400 (EDT)
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- Delivered-to: l-mathgroup@wolfram.com
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On Sunday, September 23, 2012 3:02:11 AM UTC-4, Niles wrote:
> Hi
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> I have a set of data (x, y) that I can succesfully fit a nonlinear function to using NonlinearModelFit:
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> data = {{1, 1}, {2, 2}, {3, 3.2}};
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> fitFuncExactNoLosses[a_, b_, x_] := a*x^2 + b + x;
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> nlm = NonlinearModelFit[data, fitFuncExactNoLosses[a, b, x],
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> {
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> {a, 1},
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> {b, 1}},
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> x]
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> However, the paramter "b" comes out negative and it *must* be positive. Is there a way to utilize assumptions such that b is constrained to be grater than zero?
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> Best,
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> Niels.
You could change b to b^2 in the fitting function and take the square root afterwards.