void lognormal()
{
  const int NMAX = 10;

  TF1* f[4] = { 0 }; 
  double mu[4] = { 0, 0, 1, 2 };
  double sigma[4] = { 0.5, 1, 1, 1 };

  for( int i = 0; i < 4; ++i ) {
    f[i] = new TF1( Form( "hlognormal%d", i ), 
		    lognormal, 1e-6, 5, 2 );
    f[i]->SetTitle( Form( "Log-Normal Probability: #mu = %3.1f, #sigma = %3.1f", mu[i], sigma[i] ) );
    f[i]->SetMaximum( 1.0 );
    f[i]->SetParameters( mu[i], sigma[i] );
    f[i]->SetNpx( 1000 );
    f[i]->Draw();
    f[i]->GetXaxis()->SetTitle( "x" );
    f[i]->GetYaxis()->SetTitle( "f(x;#mu,#sigma)" );

    gPad->SaveAs( Form( "lognormal%d.pdf", i ) );
  }
}

double lognormal( double* x, double* par )
{
  double val   = x[0];
  double mu    = par[0];
  double sigma = par[1];

  double arg = ( log( val ) - mu ) / sigma;

  return exp( -0.5*arg*arg ) / ( sqrt( 2*TMath::Pi() ) * sigma * val );
}