Line data    Source code

       1             : module m_DoubleFactorial
       2             : 
       3             : implicit none
       4             : 
       5             : 
       6             : contains
       7             : 
       8             :   
       9      184069 : real function DoubleFactorial( n_upper, n_lower )
      10             : ! calculates ( 2 * n_upper + 1 ) !! / ( 2 * n_lower + 1 ) !! or just ( 2 * n_upper + 1 ) !!, if n_lower is not present
      11             : 
      12             :   integer           :: n_upper
      13             :   integer, optional :: n_lower
      14             :   integer           :: i, i_lower
      15             : 
      16      184069 :   i_lower = 1
      17      184069 :   if( present(n_lower) ) i_lower = n_lower + 1
      18             : 
      19      184069 :   DoubleFactorial = 1.
      20     1025917 :   do i = i_lower, n_upper
      21     1025917 :     DoubleFactorial = DoubleFactorial * ( 2 * i + 1 )
      22             :   end do
      23             : 
      24      184069 : end function DoubleFactorial
      25             : 
      26             : 
      27             : end module m_DoubleFactorial