Moyal distribution

ROOT
1

Hello everyone,

I want to define Moyal distribution as a user defined function using ROOT. Can someone help me?

I attached the function definition also one can find the definition from ,
stat.rice.edu/~dobelman/text … ndbook.pdf
Page number is 91.

Thank you very much.

Best

moyal.png1920×1080 77.9 KB

2

Something like (not tested) should work

[code]Double_t f_Moyal(Double_t *x, Double_t par) {
return 1./TMath::Sqrt(TMath::TwoPi()) * TMath::Exp(-0.5(x[0]+TMath::Exp(-x[0])));
}

Double_t g_Moyal(Double_t *x, Double_t *par) {
return 1./par[0]*f_Moyal((x[0]-par[1])/par[0]);
}

int main() {
TF1 *f = new TF1(“f”,g_Moyal,-5,10);
f->Draw();
}[/code]

3

Thank you very much. It gave me this error :confused:

Error in TFormula::Compile: Bad numerical expression : "g_Moyal"
Error in TF1::TF1: function: f/g_Moyal has 0 parameters instead of 1
Info in TCanvas::MakeDefCanvas: created default TCanvas with name c1
Warning in TCanvas::ResizePad: c1 height changed from 64000 to 10

Error in TGaxis::PaintAxis: length of axis is 0
root [1] Warning in TCanvas::ResizePad: c1 height changed from 64000 to 10

Warning in TCanvas::ResizePad: c1 height changed from 64000 to 10

Do you know why it is?

4

I guess the reason is missing parameter. I changed abit like,

int fit() {
TCanvas *c1 = new TCanvas(“c1”, “asdf”, 1800, 800);
TF1 *f = new TF1(“f”,g_Moyal,-5,10,4);
f->SetParameter(0,140.0);
f->Draw();
}

However afterwards it gave this error,
Error: Function f_Moyal((x[0]-par[1])/par[0]) is not defined in current scope fit.C:344:
*** Interpreter error recovered ***
root [1] Error: Function f_Moyal((x[0]-par[1])/par[0]) is not defined in current scope fit.C:344:
,
Error: Symbol , is not defined in current scope (tmpfile):1:
*** Interpreter error recovered ***

Hope you can help me :slight_smile:

5

Hi,


Double_t f_Moyal(Double_t *xx, Double_t *par) {
    auto x = *xx;
    auto theexp = TMath::Exp(-0.5*(x+TMath::Exp(-x)));
    return theexp / TMath::Sqrt(TMath::TwoPi());
}

Double_t g_Moyal(Double_t *x, Double_t *par) {
    double xx = (x[0]-par[0])/par[1];
    return f_Moyal(&xx, nullptr)/par[1];
}


void moyal() {
   auto f = new TF1("f",g_Moyal,-5,10,2);
   f->SetParameters(1,1);
   auto c = new TCanvas();
   f->Draw();
}

Cheers,
Danilo

6

Thank you so much for your prompt answer and help me in this matter.

Cheers