Rene, Fons,
consider this piece of macro
Double_t expo (Double_t *xx, Double_t *){return TMath::Exp(-(*xx));}
void fca() {
gROOT->Reset();
TF1 *fun = new TF1("expo",expo,0,2,0);
fun->Draw();
//c1->Update();
TH1F *hist = fun->GetHistogram();
hist->Draw("same");
}
If you do
.L fca.C
and then type the content of the macro everything works as expected. If
you execute the macro it does not work. If you uncomment the update it
works.
The reason is simple. The fHistogram is created and filled by the Paint
method of TF1. This is called either at every return at the keyboard or by
the Update function of the canvas. But the behaviour is quite unexpected.
Somehow one would expect simple commands to behave the same way in a macro
or typed in...
Thanks to M.Kowalski for spotting this.
Ciao,
Federico Carminati
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|| Federico Carminati || Tel.: +41.22.767.4959 ||
|| CERN-EP || Fax.: +41.22.767.9075 ||
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