void graph()
{
  const int N = 10;
  float x[N] = { 1.3, 5.4, 3.2, 5.5, 8.2, 8.9, 9.0, 1.2, 0.1, 11 };
  float value[N] = { 0.5, 10.3, 3.3, 10.1, 7.0, 8.1, 9.0, 0.1, 1.0, 5.0 };
  float error[N] = { 0.3, 0.5, 0.3, 0.5, 0.3, 0.5, 0.3, 0.5, 0.3, 0.5 };

  TGraphErrors* g = new TGraphErrors( N, x, value, 0, error );
  g->SetMarkerStyle( 20 );
  g->SetMarkerSize( 1.0 );
  g->Draw( "ap" );
}