How to fit TH3 histogram

ROOT
1

Hi,
I need to fit 3D histogram with 3D function, but I can’t find
any fit method in the description of the TH3 Class.
Could you please provide me with any useful documentation.

2

see example below. Run it with
root fit3.C+

//file fit3.C
#include "TRandom3.h"
#include "TH3.h"
#include "TF3.h"
#include "TMath.h"
   
double myfunc3(double *x, double *par) {
   double xx = (x[0] - par[1])/par[2];
   double yy = (x[1] - par[3])/par[4];
   double zz = (x[2] - par[5])/par[6];
   double rx = TMath::Exp(-xx*xx);
   double ry = TMath::Exp(-yy*yy);
   double rz = TMath::Exp(-zz*zz);
   double result = par[0]*rx*ry*rz;
   return result;
}
void fit3() {
   TH3F *h3 = new TH3F("h3","test",40,-3,3,40,-3,3,40,-4,4);
   TRandom3 r;
   for (int i=0;i<100000;i++) {
      double x = r.Gaus(-0.2,0.6);
      double y = r.Gaus(0.3,0.5);
      double z = r.Gaus(0,1);
      h3->Fill(x,y,z);
   }
   TF3 *func3 = new TF3("func3",myfunc3,-3,3,-3,3,-4,4,7);
   func3->SetParameters(h3->GetMaximum(),0,0.5,0,0.5,0,0.5);
   h3->Fit(func3);
}

Rene

3

Thank you!!!