void chi2() { TF1* fG = new TF1( "Gamma", "TMath::Gamma(x)", 0, 5 ); fG->Draw(); fG->GetXaxis()->SetTitle( "x" ); fG->GetYaxis()->SetTitle( "#Gamma(x)" ); gPad->SaveAs( "Gamma.pdf" ); TF1* f[3] = { 0 }; int n[3] = { 8,9,10 }; for( int i = =; i < 3 ; ++i ) { f[i] = new TF1( Form( "fchi2%d", i ), chisquare, 0, 20, 1 ); f[i]->SetTitle( Form( "#chi^{2}-Verteilung: n = %d", n[i] ) ); f[i]->SetMaximum( 0.5 ); f[i]->SetParameter( 0, n[i] ); f[i]->SetNpx( 1000 ); f[i]->Draw(); f[i]->GetXaxis()->SetTitle( "x" ); f[i]->GetYaxis()->SetTitle( "#chi^{2}(x;n)" ); gPad->SaveAs( Form( "chisquare%d.pdf", i ) ); } } double chisquare( double* x, double* par ) { double val = x[0]; double nhalf = 0.5 * par[0]; return pow( val, nhalf - 1.0 ) * exp( -0.5*val ) / ( pow( 2, nhalf ) * TMath::Gamma( nhalf ) ); }