Re: [ROOT] fitting

From: Stephen Bailey (bailey@physics.harvard.edu)
Date: Wed Jun 28 2000 - 00:10:40 MEST


Hi Kevin.

To use combinations of predefined functions, you have to
first create a function that is that combo, and then fit
using that function:

  TF1* f1 = new TF1("f1", "gaus(0)+expo(3)");
  f1->SetParameters(1, 2, 3, 4, 5);  // or some reasonable start values
  h1->Fit("f1");     //  NB: h1->Fit("gaus(0)+expo(3)") won't work

To the ROOT developers:  I know this seems to be a trivial
amount of typing to achieve combo fits, but easy and quick
fitting using different combinations of functions is something
I miss from the old PAW / MinFit days.  If syntax like

  h1->Fit("gaus(0)+expo(3)+(3*x-1)");

could be added, it would be a nice feature to have.  Perhaps
if the string isn't recognized as a function name, you could
attempt to parse it and create a temporary function (similar
to how TTree::Draw() creates a temporary histogram) and fit
using that function.

Happy fitting,

Stephen


On Tue, 27 Jun 2000, Kevin M. Rhodes wrote:

> I'm trying to fit an histogram with a simple addition of two root-defined
> functions, by doing gaus+expo.  Is there something special that I need to
> do to get this to work?
> 
> 
> Kevin Rhodes
> UW Madison
> Amanda Project
> 



This archive was generated by hypermail 2b29 : Tue Jan 02 2001 - 11:50:29 MET