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f6bacaf83   cwaterkeyn   ChW 11/09: ANSI c... 
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  function dbesyn(n,x)
8d883e8a1   wdaniau   Integration of ki... 
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      use fvn_common
e1aefab23   daniau   git-svn-id: https... 
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      implicit none
      ! This function compute the rank n Bessel Y function
      ! using recurrence relation :
      ! Yn+1(x)=2n/x * Yn(x) - Yn-1(x)
      !
f6bacaf83   cwaterkeyn   ChW 11/09: ANSI c... 
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      real(dp_kind) :: dbesyn
e1aefab23   daniau   git-svn-id: https... 
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      integer :: n
f6bacaf83   cwaterkeyn   ChW 11/09: ANSI c... 
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      real(dp_kind) :: x
e1aefab23   daniau   git-svn-id: https... 
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f6bacaf83
 
 cwaterkeyn
 
ChW 11/09: ANSI c...




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      real(dp_kind),external :: dbesy0,dbesy1
      real(dp_kind) :: two_on_x,bynm1,byn,bytmp









e1aefab23
 
 daniau
 
git-svn-id: https...




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      integer :: i
  
      if (n==0) then
          dbesyn=dbesy0(x)
          return
      end if
      if (n==1) then
          dbesyn=dbesy1(x)
          return
      end if
      if (n < 0) then
          write(*,*) "Error in dbesyn, n must be >= 0"
          stop
      end if
      if (x <= 0.) then
          write(*,*) "Error in dbesyn, x must be strictly positive"
      end if
  
      two_on_x=2./x
      bynm1=dbesy0(x)
      byn=dbesy1(x)
  
      do i=1,n-1
          bytmp=two_on_x*byn*i-bynm1
          bynm1=byn
          byn=bytmp
      end do
      dbesyn=bytmp
  end function