function integr = integrale_formula( f , ab , n , formula )
  n = 2 * floor( n / 2 ) ;
  x = linspace( ab(1) , ab(2) , n+1 ) ;
  dx = x(2) - x(1) ;
  f_x = f( x ) ;
  switch formula
    case 1 % Trapezi
      estremi = f_x(1) + f_x(end) ;
      interni = 2 * sum( f_x(2:end-1) ) ;
      integr  = (dx/2) * ( estremi + interni ) ;
    case 2 % Simpson
      estremi = f_x(1) + f_x(end) ;
      interni_pari    = 4 * sum( f_x(2:2:end-1) ) ;
      interni_dispari = 2 * sum( f_x(3:2:end-2) ) ;
      integr  = (dx/3) * ( estremi + interni_pari + interni_dispari ) ; 
  end
end