Fitting a piecewise continuous Function
- To: mathgroup at smc.vnet.net
- Subject: [mg16646] Fitting a piecewise continuous Function
- From: Jason Gill <jgill at vbimail.champlain.edu>
- Date: Fri, 19 Mar 1999 12:54:00 -0500
- Organization: IBM Microelectronics
- Sender: owner-wri-mathgroup at wolfram.com
Folks, I am trying to fit a piecewise continuous function to some data. Here is a simple example, I hope someone can help me out with. Here I have a function In[69]:= testF[t_]:=r0/;t<ti; testF[t_]:=r0+5*(t-ti)/;t>=ti; If I define values for r0 & ti, r0=5; ti=11; This function is continuous and may be plotted. In[75]:= Plot[testF[t],{t,0,15}] Graphic Not included. The question is, how can I perform a NonlinearFit using the above function to some data. Suppose I have the sample data below, how do I Fit the function to the data, with fit parameters. r0, and ti. Sample data: data1=Table[5,{i,1,10}]; data2=Table[5*i,{i,1,10}]; data=Transpose[{Range[Length[Join[data1,data2]]],Join[data1,data2]}]; I tried (after clearing the values for r0 & t) to perform a NonlinearFit In[7]:= NonlinearFit[data,testF[t],{t},{{r0,5},{ti,10}}] Out: The model is not numerical at {r0->5,ti->10,t->1}. but this does not work. What technique do I need to use to get Mathematica to perform the fit as I have described? What am I missing? Any suggestions would be welcome. Thanks, Jason