[ROOT] Fit function compiling problems

From: Daniel Bowerman (bowerman@SLAC.stanford.edu)
Date: Thu Feb 01 2001 - 19:50:17 MET 

Hi rooters,

I'm trying to perform a fit within a loop and then access the fit
parameters. I construct a TProfile histogram and a TF1 using my own
function. I fill the TProfile and perform the fit. The fit works perfectly
the first time round but I then get error messages such as
"Function:myfunc cannot be compiled" where myfunc is the function I've
defined. Consequently the fit doesn't work for any other passes of the loop.

The function is defined by:

Double_t myfit(Double_t *x, Double_t *par){

  Double_t xval = x[0];
  Double_t xfit = 0;
  if(xval<par[0]){
    xfit = par[2]+(par[3]*(xval+100));
  }
  if(xval>par[0]&&xval<par[1]){
    xfit = (par[2]+par[3]*(par[0]+100))+(par[4]*(xval-par[0]));
  }
  if(xval>par[1]){
    xfit =
(par[2]+par[3]*(par[0]+100))+(par[4]*(par[1]-par[0]))+par[5]*(xval-par[1]);
  }
  return xfit;
}


And the code of interest in the macro is:

for(Int_t c = 0; c<3; c++){
     TProfile *xtalfit = new TProfile("xtalfit","xtalfit",1600,
						-200,1400,200,400);
     TF1 *func = new TF1("myfunc",myfit,-100,1300,6);
     func->SetParLimits(0,550,725);
     func->SetParLimits(1,750,900);

     Int_t nbytes = 0;
     Int_t noentries = h6->GetEntries();
     for (Int_t i=0; i<noentries;i++) {
       nbytes += h6->GetEntry(i);
       if(channel==c&&(channel>chann || etc...

	//Fill the Profile histogram
	 xtalfit->Fill(xpoint,ypoint);
       }
     }

     // Perform the fit
     xtalfit->Draw();
     xtalfit->Fit("myfunc","","",-100,1300);

     // access the parameters
     param0 = func->GetParameter(0);
     param1 = func->GetParameter(1);

     // clean up - doesn't make any difference
     delete xtalfit;
     delete func;
}


Sorry if I'm missing something obvious but any help you can provide is
much appreciated.

Thanks,
Dan.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	Daniel Bowerman				|Tel: +1-650-926-2767
	Imperial College			|Fax: +1-650-926-3767
	Stanford Linear Accelerator Center	|
	M/S 59, P.O. Box 4349 			|
	Stanford, CA 94309, USA                 |bowerman@SLAC.Stanford.edu

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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