{
gStyle->SetOptFit(1);
TCanvas* c1 = new TCanvas("c1","c1",800,600);
c1->Divide(2,2);

TH1F* hist = new TH1F("hist","hist",1000,300,500);
TF1* func = new TF1("func","[2]*TMath::Gaus(x,[0],[1])+[3]*x+[4]");
func->SetParNames("mean","sigma","area","slope","offset");
func->SetParameters(400.,10.,1000.,-10,5000);
hist->FillRandom("func",1000000);
TH1F* hist2 = (TH1F*) hist->Clone("hist2");

func->SetParameters(420.,50.,100.,-1,3000);
c1->cd(1);
hist->Fit(func);

TH1F* hist1 = (TH1F*) hist->Clone("hist1");
hist1->Draw();
TH1F* hist3 = (TH1F*) hist->Clone("hist3");

func->SetParameters(420.,50.,100.,-1,3000);
c1->cd(2);
hist->Fit(func);

func->SetParameters(420.,50.,100.,-1,3000);
c1->cd(3);
hist2->Fit(func);

func->SetParameters(420.,50.,100.,-1,3000);
c1->cd(4);
hist3->Fit(func);
}