Re: Getting parameters from Fit[]..

*To*: mathgroup at smc.vnet.net*Subject*: [mg27108] Re: Getting parameters from Fit[]..*From*: "Paul Lutus" <nospam at nosite.com>*Date*: Sun, 4 Feb 2001 02:58:35 -0500 (EST)*References*: <95gkss$8do@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

"Mark Harder" <harderm at ucs.orst.edu> wrote in message news:95gkss$8do at smc.vnet.net... > > 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? There are many ways to isolate specific parts of the output of a function such as Fit[]. Perhaps you could post an example of your specific problem. Using this example, one of us can show how to obtain a subset of the output. And your use of the expression "parameters" is open to interpretation. Perhaps this example will show you how to acquire specific values: In[126]:= data = Table[Random[]+x+5,{x,0,10}] Out[126]= {5.42144,6.9507,7.81605,8.58055,9.52052,10.4903,11.862,12.8759,13.2112,14.04 31,15.2096} In[166]:= fd = Fit[data, {1,x} ,x] (* m x + b form *) Out[166]= 4.84769 + 0.949344 x In[167]:= {b,m}= {fd[[1]],fd[[2,1]]} Out[167]= {4.84769,0.949344} -- Paul Lutus www.arachnoid.com