Re: Evaluateing functions with TF1::EvalPar

Rene Brun (Rene.Brun@cern.ch)
Fri, 06 Mar 1998 09:07:05 +0100

I have modified the body of your macro below.
You were using TF1::EvalPar. This function requires a prior
initialisation of the parameters via TF1::InitArgs before calling it
in the case where the function is an interpreted function.
This feature is unfortunately not documented. I have put the info
in the new version of EvalPar. Thanks for reporting this anomaly.

Rene Brun

> {
gROOT->Reset();
gStyle->SetOptFit(1);
gStyle->SetStatX(0.45);
gStyle->SetStatY(0.85);

TCanvas* c1 = new TCanvas("c1","Ntuple Plots",1); // create canvas
c1->SetFillColor(kWhite);

TFile* f1 = new TFile("cjj_g10.root","READ");
TH1F* hi1 = new TH1F("hi1","Angular Resolution: Gamma Energy = 10 MeV
",80,-1.0,1.0);
hi1->SetXTitle("Cos`q#");
// h509->Draw("Angres>>hi1","Egen>4&&Rfitt<600","goff");
h503->Draw("(Ue*Uf+Ve*Vf+We*Wf)>>hi1","Rfit<600","goff");
c1->SetLogy(1);
TF1* expExp = new TF1("expExp",expExp,-1,1,4);
expExp->SetParameters(9.2,0.2,5.7,17000);
expExp->SetParNames("1st slope","2nd Amp","2nd slope","scale fac");
Double_t x;
Double_t y;
printf("Hello\n");
for( Int_t i=0 ; i<80 ; i++) {
x = -0.9875+i*0.025;
y = expExp->Eval(x);
printf("%d\t%f\t%f\t%f\n",i,hi1->GetBinContent(i),x[0],y);
}
expExp->Draw();
/* expExp->SetParLimits(0,9.2,9.3);
expExp->SetParLimits(1,0.2,0.21);
expExp->SetParLimits(2,5.7,5.8);
expExp->SetParLimits(3,17000.0,17100.0);

TPostScript ps("cjj_g10.eps",114);
hi1->Fit("expExp","RB");
// expExp->Draw();
// hi1->Draw("same");
c1->Update();
ps.Close();
*/

}

>Chris Jillings wrote:
> Hi,
> The follwing macro fails to calculate
> y = expExp->EvalPar(x,a);
>
> At the prompt I type
> .L expExp.C
> .x cjj_g10.C
>
> All values printed to screen for y are 0. Everything is printed
> correctly. Any ideas? Also, is it possible to subtract a function from a
> histgram to get the residuals of a fit, say. This feature would be very
> nice if it is not currently in place.
>
> I am running 1.03/09 on a linux box.
>
> Thanks,
>
> Chris
>
> The complete macro follows
>
> {
> gROOT->Reset();
> gStyle->SetOptFit(1);
> gStyle->SetStatX(0.45);
> gStyle->SetStatY(0.85);
>
> TCanvas* c1 = new TCanvas("c1","Ntuple Plots",1); // create canvas
> c1->SetFillColor(kWhite);
>
> TFile* f1 = new TFile("cjj_g10.root","READ");
> TH1F* hi1 = new TH1F("hi1","Angular Resolution: Gamma Energy = 10 MeV ",80,-1.0,1.0);
> hi1->SetXTitle("Cos`q#");
> // h509->Draw("Angres>>hi1","Egen>4&&Rfitt<600","goff");
> h503->Draw("(Ue*Uf+Ve*Vf+We*Wf)>>hi1","Rfit<600","goff");
> c1->SetLogy(1);
> TF1* expExp = new TF1("expExp",expExp,-1,1,4);
> expExp->SetParameters(9.2,0.2,5.7,17000);
> expExp->SetParNames("1st slope","2nd Amp","2nd slope","scale fac");
> Double_t x[1];
> Double_t a[4];
> a[0] = 9.2;
> a[1] = 0.2;
> a[2] = 5.7;
> a[3] = 17000.0;
> Double_t y;
> printf("Hello\n");
> for( Int_t i=0 ; i<80 ; i++) {
> x[0] = -0.9875+i*0.025;
> y = expExp->EvalPar(x,a);
> printf("%d\t%f\t%f\t%f\n",i,hi1->GetBinContent(i),x[0],y);
> }
> expExp->Draw();
> /* expExp->SetParLimits(0,9.2,9.3);
> expExp->SetParLimits(1,0.2,0.21);
> expExp->SetParLimits(2,5.7,5.8);
> expExp->SetParLimits(3,17000.0,17100.0);
>
> TPostScript ps("cjj_g10.eps",114);
> hi1->Fit("expExp","RB");
> // expExp->Draw();
> // hi1->Draw("same");
> c1->Update();
> ps.Close();
> */
>
> }
>
> The function expExp is ...
>
> Double_t expExp(Double_t* x, Double_t* par) {
> Double_t expPart1 = exp(par[0]*(x[0]-1));
> Double_t expPart2 = exp(par[2]*(x[0]-1));
>
> return (par[3]* (expPart1 + par[1]*expPart2));
>