Rene Brun
Petar Maksimovic wrote:
>
> Hi Rooters,
>
> I would like to be able to combine TF1 objects into compound
> functions, just like one can do with the TFormula objects.
> Let me remind of you of an example that was bandied about
> this list a few months ago:
>
> Rene Brun wrote:
> > Hi Thierry,
> > I have no problems executing your macro. I have made slight changes
> > to show two functions on the same graph.
> > A similar example is given in tutorials/fillrandom.C
> > I assume you run with 2.00/13 or 2.20.
> >
> > Rene Brun
> >
> > {
> > gROOT->Reset();
> > TFormula *pomeron = new
> > TFormula("pomeron","[0]*pow((x-0.939*0.939)/1.878,[1])");
> > TFormula *f = new
> > TFormula("f","([2]*pow((x-0.939*0.939)/1.878,[3]))");
> > TF1 *total = new TF1("total","pomeron + f",1,20);
> > total->SetParameters(1,2,1.5,2.4);
> > total->Draw();
> > TF1 *one = new TF1("one","pomeron",1,20);
> > one->SetParameters(1,2,1.5);
> > one->Draw("same");
> > }
>
> What I have in mind is to be able to use TF1's associated with
> user-defined functions (a.k.a. "type C"). Since the above example works,
> and TF1 *is a* TFormula, I would naively expect that the following
> example should work as well:
>
> -------------8<--------------------------------------------
> Double_t internalFunA(Double_t *x, Double_t *par)
> {
> return x[0]*0.1 + 5.0;
> }
>
> Double_t internalFunB(Double_t *x, Double_t *par)
> {
> return x[0]*x[0]*77;
> }
>
> void test(void)
> {
> TF1 myFuncA("myA", internalFunA, 0.0, 0.4, 1); // myA is a TFormula
> TF1 myFuncB("myB", internalFunB, 0.0, 0.4, 1); // myB is a TFormula
> TF1 myFuncAB("myAB", "myA + myB", 0.0, 0.4 ); // this doesn't work
> }
> -------------8<--------------------------------------------
>
> However it fails when trying to construct myFuncAB:
>
> *ERROR 26 :
> Unknown name : "myA"
>
> Am I doing something wrong here?
>
> To summarize:
> - it would be really nice to be able to do something like this (so
> that one can build very complex fits by building functions from
> smaller -- but also non-trivial -- functions)
>
> - if TF1 is a TFormula, I would expect this to work
>
> I might be missing something, and perhaps the above behavior is
> expected. If that's so, please let me know how one can get
> around it...
>
> Thanks a lot!
>
> Petar