Re: conditionals during nonlinear regression

*To*: mathgroup at smc.vnet.net*Subject*: [mg28426] Re: [mg28420] conditionals during nonlinear regression*From*: BobHanlon at aol.com*Date*: Wed, 18 Apr 2001 03:23:29 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Make ds a parameter of the model model = (2-ds)*(a1*Exp[m]+b1)+(ds-1)*(a2*Exp[m]+b2); model /. {{ds -> 1}, {ds -> 2}} {E^m*a1 + b1, E^m*a2 + b2} model = (2-ds)*(3-ds)*(a1*Exp[m]+b1)/ 2+(ds-1)*(3-ds)*(a2*Exp[m]+b2) + (ds-1)*(ds-2)*(a3*Exp[m]+b3)/2; model /. {{ds -> 1}, {ds -> 2}, {ds -> 3}} {E^m*a1 + b1, E^m*a2 + b2, E^m*a3 + b3} Bob Hanlon In a message dated 2001/4/17 1:48:08 AM, baker at fas.harvard.edu writes: >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? >