1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
|
! Copyright (C) 2002-2005 J. K. Dewhurst, S. Sharma and C. Ambrosch-Draxl.
! This file is distributed under the terms of the GNU Lesser General Public
! License. See the file COPYING for license details.
!BOP
! !ROUTINE: factr
! !INTERFACE:
real(8) function factr(n,d)
! !INPUT/OUTPUT PARAMETERS:
! n : numerator (in,integer)
! d : denominator (in,integer)
! !DESCRIPTION:
! Returns the ratio $n!/d!$ for $n,d\ge 0$. Performs no under- or overflow
! checking.
!
! !REVISION HISTORY:
! Created October 2002 (JKD)
!EOP
!BOC
implicit none
! arguments
integer, intent(in) :: n,d
! local variables
integer i
! external functions
real(8), external :: factn
if (d == 1) then
factr=factn(n)
return
end if
if ((n < 0).or.(d < 0)) then
factr=0.d0
return
end if
if (n < d) then
factr=dble(n+1)
do i=n+2,d
factr=factr*dble(i)
end do
factr=1.d0/factr
else if (n == d) then
factr=1.d0
else
factr=dble(d+1)
do i=d+2,n
factr=factr*dble(i)
end do
end if
end function
!EOC
|
