delfra.f

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!                   ***************
                    FUNCTION delfra
!                   ***************
!
     &( ss    )
!
!***********************************************************************
! TOMAWAC   V6P1                                   14/06/2011
!***********************************************************************
!
!brief    COMPUTES THE COEFFICIENT THAT NORMALISES THE DIRECTIONAL
!+                SPREADING FUNCTION IN COS **2.S (TETA-TETA0).
!code
!+                               GAMMA( SS + 0.5)
!+        DELFRA(SS) = SQRT(PI)  ----------------
!+                               GAMMA( SS + 1. )
!
!history  M. BENOIT
!+        15/11/95
!+        V1P0
!+   CREATED
!
!history  M. BENOIT
!+        07/11/96
!+        V1P2
!+   MODIFIED
!
!history  N.DURAND (HRW), S.E.BOURBAN (HRW)
!+        13/07/2010
!+        V6P0
!+   Translation of French comments within the FORTRAN sources into
!+   English comments
!
!history  N.DURAND (HRW), S.E.BOURBAN (HRW)
!+        21/08/2010
!+        V6P0
!+   Creation of DOXYGEN tags for automated documentation and
!+   cross-referencing of the FORTRAN sources
!
!history  G.MATTAROLO (EDF - LNHE)
!+        15/06/2011
!+        V6P1
!+   Translation of French names of the variables in argument
!
!~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!| DEUPI          |-->| 2.PI
!| SS             |-->| EXPONENT OF THE DIRECTIONAL SPREADING FUNCTION
!~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!
      USE interface_tomawac, ex_delfra => delfra
      USE declarations_tomawac, ONLY : deupi
      IMPLICIT NONE
!
!.....VARIABLES IN ARGUMENT
!     """""""""""""""""""""
      DOUBLE PRECISION DELFRA, SS
!
!.....EXTERNAL FUNCTIONS
!     """"""""""""""""""
!      DOUBLE PRECISION GAMMLN
!      EXTERNAL         GAMMLN
!
!
      delfra=sqrt(deupi/2.d0)
     &      *exp(gammln(ss+0.5d0,deupi)-gammln(ss+1.d0,deupi))
!
      RETURN
      END