ADAS Subroutine a8slvf

       subroutine a8slvf(itype,xk,sigk,xn,sign,s,f2,f3,ifail)
c-----------------------------------------------------------------------
c
c  ********************* fortran77 subroutine a8slvf *******************
c
c  purpose: to find the approximate form parameters f2 and f3 for 
c           neutrals
c
c  calling program:  adas108.for
c
c  input:
c            (i*4)  itype    = type of transition (1=dipole,2=non-dipole
c                              non-spin change, 3=spin change, 4=null)
c            (r*8)  xk       = x-parameter at matching point k
c            (r*8)  sigk     = collisions strength at matching point k
c            (r*8)  xn       = x-parameter at last energy point n
c            (r*8)  sign     = collisions strength at last energy pt. n 
c            (r*8)  s        = line strength for type 1 case 
c            (i*4)  ifail    = failure code  on entry (ifail=0 two point
c                              fit, ifail=-1 one point fit)
c  output: 
c            (r*8)  f2       = asymptotic form parameter
c            (r*8)  f3       = asymptotic form parameter
c            (i*4)  ifail    = failure code  on exit 
c                             (ifail=0 successful two point fit
c                              ifail=1 converted to one point fit)
c 
c
c  routines: none
c
c  author:   Hugh Summers, University of Strathclyde ext.4196
c
c
c  version 1.1                             date:     15/06/99
c  modified: Hugh Summers
c		- first release
c
c-----------------------------------------------------------------------
      INTEGER             IFAIL,       ITYPE
      REAL*8              F2,          F3,          S,           SIGK
      REAL*8              SIGN,        XK,          XN