void funktion()
{
  TF1* f1 = new TF1( "f1", "exp(-x)*x", 0, 10 );
  f1->Draw();

  TF2* f2 = new TF2( "f2", func2, -10, 10, -10, 10, 0 );
  f2->Draw( "surf" );
}

double func2( double* val, double* par )
{
  double x = val[0];
  double y = val[1];
  return sin(x)*sin(y)/(x*y);
}