void transformation()
{
  double xmax = 5;

  TH1* h = new TH1F( "h", "Transformationsmethode", 10, 0, xmax );
  h->SetMaximum( 1 );
  h->SetStats( kFALSE );
  h->Draw();

  TH1* hdist = new TH1F( "hdist", "Histogramm fuer Zufallszahlen", 10, 0, xmax );

  TF1* f = new TF1( "f", "exp(-x)", 0, xmax );
  f->Draw("same");

  TF1* F = new TF1( "F", "1-exp(-x)", 0, xmax );
  F->SetLineColor( 4 );
  F->Draw("same");

  TLine* lx = 0;
  TLine* ly = 0;
  TH1* hsave = 0;

  for( int i = 0; i < 1000; ++ i ) {

    if( lx != 0 ) delete lx;
    if( ly != 0 ) delete ly;
    if( hsave != 0 ) delete hsave;
    
    double y = gRandom->Uniform();
    double x = -log( y );
    cout << i << "\t" << y << "\t" << x << endl;
    
    hdist->Fill( x );
    TH1* hsave = hdist->DrawNormalized( "same" );

    // correct by 1/(bin width)
    hsave->Scale( 10/xmax );

    lx = new TLine( x, 0, x, 1 );
    lx->Draw();

    ly = new TLine( 0, y, xmax, y );
    ly->Draw();

    gPad->Modified();
    gPad->Update();
    if( i < 10 ) gPad->WaitPrimitive();

  }
}