ADAS Subroutine a8optm

       subroutine a8optm(itype,xa,oa,n,s,b0,bp0,f10,f20,f30,xk0,ifail)
c-----------------------------------------------------------------------
c
c  ********************* fortran77 subroutine a8optm *******************
c
c  purpose: to find the best approximate form parameters for neutral
c           atoms by varing the matching position. 
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)  xa()     = x-parameters for cross-section
c            (r*8)  oa       = collisions strengths for transition
c            (i*4)  n        = no of collision strengths
c            (r*8)  s        = line strength if dipole transition
c            (i*4)  ifail    = failure code  on entry (ifail=0 two point
c                              fit, ifail=-1 one point fit)
c  output: 
c            (r*8)  b0       = threshold form parameter
c            (r*8)  bp0      = matching parameter
c            (r*8)  f10      = threshold form parameter
c            (r*8)  f20      = asymptotic form parameter
c            (r*8)  f30      = asymptotic form parameter
c            (r*8)  xk0      = optimum matching x-value
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: 
c             a8slvf	adas	solves for asymptotic parms f2 and f3
c	      a8slv2	adas    solves for the parms f1,f2,f3,b
c
c  author:   Hugh Summers, University of Strathclyde ext.4196
c
c
c  version 1.1                             date:     19/07/99
c  modified: Hugh Summers
c		- first release
c
c-----------------------------------------------------------------------
      INTEGER             IFAIL,       ITYPE,       N
      REAL*8              B0,          BP0,         F10,         F20
      REAL*8              F30,         OA(N),       S,           XA(N)
      REAL*8              XK0