Re: conditionals during nonlinear regression

*To*: mathgroup at smc.vnet.net*Subject*: [mg28421] Re: [mg28420] conditionals during nonlinear regression*From*: "Mark Harder" <harderm at ucs.orst.edu>*Date*: Wed, 18 Apr 2001 03:23:24 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Brian, Since you don't provide the error message(s) you were given or your relevant code, its a little hard to give a definite answer. It sounds like you want to provide NonlinearRegress with a numerical list in the required form, in which x1,x2,x3 *and* ds are the independent variables. However, your failure to list ds as an independent variable along x1,x2, & x3 makes me think you might not have handled the listing of the numeric values and/or the symbolic variable list correctly. When you use ds as the deciding variable in the If[], you must list it as part of the 3rd argument to NonlinearRegress, ie {x1,x2,x3,ds}. Next, you must make sure that the model function uses these exact symbols as its independent variables, otherwise, Mathematica won't "know" which column of your data matrix goes where in your model (I mention this because you didn't include x1,x2,x3 in your example function.) And, finally, your data matrix does have 1,1,1,...., 2,2,2... as the values in the 4th column doesn't it? If you have already followed these instructions, and Mathematica is still upset with you, you might have to provide us with more info, assuming no one else comes up with the solution. -mark harder harderm at ucs.orst.edu -----Original Message----- From: news.fas.harvard.edu <baker at fas.harvard.edu> To: mathgroup at smc.vnet.net Subject: [mg28421] [mg28420] conditionals during nonlinear regression >Greetings all, I'm new at this so please try to bear with me. >I'm trying to use NonlinearRegress to simultaneously fit multiple datasets, >each dataset described by some global (shared) parameter as well as local >parameters. I have one big list of the type {x1,x2,x3,ds,y}, where x1-x3 are >independent variables for each dataset, and ds indicates the dataset number. >In the old-fashioned fortran and C fitting packages I used to use, I just >used If statements to test which dataset was being fitted and setup the >function appropriately. If I try to do this with Mathematica, it yells at >me. For a basic example, if I have two datasets with ds=1 or 2, I try as the >fitting function > >If[ds==1,a1*Exp[m]+b1,a2*Exp[m]+b2] > >I can fit data just fine if I limit things to one dataset and leave out the >conditional statements. But anything more complicated doesn't work. Any >advice? > >Thanks, >-Brian >baker at crystal.harvard.edu > > > > >