See the documentation of classes TF1 and TFormula:
http://root.cern.ch/root/htmldoc/TF1.html
http://root.cern.ch/root/htmldoc/TFormula.html
In particular in TF1 the following paragraph:
TF1 objects can reference other TF1 objects (thanks John Odonnell)
of type A or B defined above.This excludes CINT interpreted functions
and compiled functions.
However, there is a restriction. A function cannot reference a basic
function if the basic function is a polynomial polN.
You can find a list of expressions/codes accepted in the basic functions
at:
http://root.cern.ch/root/htmldoc/TFormula.html#TFormula:Analyze
Rene Brun
On
Sat, 12 Jun 2004,
Stilianos Kesisoglou wrote:
> Hi,
>
> I've encountered a problem when I was trying to combine two TF1
> functions,
> and I am not sure if this is my mistake or is not implemented on ROOT yet.
>
> If I define:
>
> TF1 *bf = new TF1("bf","[0]+[1]*exp([2]*x)");
> TF1 *sf = new TF1("sf","[0]*exp(-0.5*(x-[1])*(x-[1])/[2]/[2])");
>
> and then:
>
> TF1 *tf = new TF1("tf","bf+sf");
>
> I get what I expect (i.e a function wich is the sum of the other
> ones).
> But if the one of the two is a user made function it fails, for
> example
> I want to use an asymmetric Gaussian for the signal:
>
> Double_t SkewGauss(Double_t *x, Double_t *pars)
> {
> here follows the definition of the function
> }
>
> then the following fails:
>
> TF1 *bf = new TF1("bf","[0]+[1]*exp([2]*x)");
> TF1 *sf = new TF1("sf",SkewGauss,4);
>
> and then:
>
> TF1 *tf = new TF1("tf","bf+sf");
>
> Is there anyway to do the above? Is there a canned SkewGauss
> function?
> (that would solve the problem).
>
> Stelios.
>
> P.S Is there any list of the canned functions that ROOT knows? I was
> looking some
> examples when I saw that ROOT knows about the "xygaus" which I
> didn't knew.
> Is there anywhere a list of all known functions?
>
>
>
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