double fitf(Double_t *x,Double_t *par){

double fitval=(par[0]*x[0]+par[1]*x[1]+par[2]);
        return fitval;
}


void rr()
{
	const int bin=40;
TCanvas *c=new TCanvas("c","c",800,600);
c->cd();
	TH3F *h=new TH3F("h","h",bin,0,50,bin,0,50,bin,0,50);
TRandom ran;
double nn=22;
const int N=5000;
double xx[N]={0};
double yy[N]={0};
double zz[N]={0};
for(int i=0;i<5000;i++){
     h->Fill(ran.Poisson(nn),ran.Poisson(nn),ran.Poisson(10)+10);
}
cout<<N<<endl;;
TF2  *f1 = new TF2("f1",fitf,0,50,0,50,3);
f1->SetParameters(1,1,10);
f1->SetMinimum(0);
f1->SetMaximum(50);
h->Fit(f1);
f1->Draw("surf2");
h->Draw("same BOX2 Z");

}