Integral of TSpline

ROOT
1

Dear all:

     How can I integrate the fitting result of TSpline3 ? There is no something 

 like TSpline3::Integral ?

     By the way, for interpolating a discrete data,the TSpine function is not bad. 

 But the documentation of this function is poor. For example,what are the choices

 of the "opt" argument ? I can't find it. 


  Thanks,
  Jack
2

Of which interpolation function are you talking about in TSpline? Eval? but is does not have any option.
Although I agree it would be nice to have a TSpline::Integral, you can easily build a TF1 with a C function and in this C function call TSpline::Eval

Rene

3

Dear Rene:

   Maybe I don't fully understand "TSpline" or I misunderstand what you mean.

I tried but still fail. Here is my code:

void interpolation2(void)
{
int x[10]={1,2,3,4,5,6,7,8,9};
int y[10]={1,2,3,4,5,4,3,2,1};

  TGraph *mygra=new TGraph(10,x,y);
  TSpline3 *s=new TSpline3("s",mygra);

  TF1 *formula=new TF1("formula","s->Eval(x)",1,9);

// TF1 *formula=new TF1(“formula”,“mygra->Eval(x)”,1,9); (<-- still fail)

  mygra->Draw("AC*");
  formula->Draw("same");

}

The error message is :

Error in <TFormula::Compile>:  Bad numerical expression : "s.Eval(x)"
Error in <TF1::TF1>: function: formula/s->Eval(x) has 0 parameters instead of 1

=========================================================

I need to calculate a integration whose integrand formed by timing this interpolation

result with another theoretical function(blackbody formula actually). So I need to

transform this discrete data points to a normal and usable function. Or any other

way I can do?

Thank you very much,
Jack.