Re: Getting parameters from Fit[]..

*To*: mathgroup at smc.vnet.net*Subject*: [mg27136] Re: [mg27055] Getting parameters from Fit[]..*From*: "Mark Harder" <harderm at ucs.orst.edu>*Date*: Wed, 7 Feb 2001 02:12:43 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Thank you all for responding so quickly to my request. You are correct about Regress. It does not print when terminated with a semicolon (as expected). I don't understand why this did not work for me before. -mark -----Original Message----- From: BobHanlon at aol.com <BobHanlon at aol.com> To: mathgroup at smc.vnet.net <mathgroup at smc.vnet.net> Subject: [mg27136] Re: [mg27055] Getting parameters from Fit[].. > >Needs["Statistics`LinearRegression`"]; > >data={{0.055,90},{0.091,97},{0.138,107},{0.167,124},{0.182,142},{0.211, > 150},{0.232,172},{0.248,189},{0.284,209},{0.351,253}}; > >funcs = {1, x, x^2}; > >bfp=(BestFitParameters /. > Regress[data, funcs, x, RegressionReport -> BestFitParameters]); > >bfp.funcs == Fit[data, funcs, x] > >True > >funcs = {1, x^2}; > >bfp=(BestFitParameters /. > Regress[data, funcs, x, RegressionReport -> BestFitParameters]); > >bfp.funcs == Fit[data, funcs, x] > >True > >Bob Hanlon > >In a message dated 2001/2/3 5:25:07 AM, harderm at ucs.orst.edu writes: > >>I am doing a linear fit to obtain parameters for use in a larger, >>iterative procedure (a separable linear-nonlinear data fitting >>algorithm), and I'm trying to use Fit[] to do this. Unfortunately, Fit >> >>does not return parameters by themselves, just the linear combination of >> >>my basis functions(which are much more complicated than the usual >>examples given in the documentation) weighted by the parameters. I have >> >>tried various things, like using Regress instead of Fit, but that prints >> >>out at least a written report of the parameters every time it is >>invoked, which will make for a very cluttered output when included in >>the larger problem I am trying to solve. I suppose I can find a method >> >>to isolate just the parts of the output of Fit that contain the >>parameters and process them to get the parameters, but that seems >>awkward and might introduce numerical errors. I've looked at the >>MathGroup archives and found only 1 response to this question in the >>past, which was "Sorry, dont know how to do that. why don't you use >>Regress?". >> Doesn't Mathematica provide any simple method for recovering just >>the parameter vector from a linear fit? If it doesn't, perhaps it ought >> >>to. Alternatively, is there some way to get Regress to provide the >>BestFitParameters rules without printing them out? Or, is there some >>*simple* and accurate way of getting the parameters from the Fit output >> >>as is? >>