double precision function d9lgic (a, x, alx)
  c july 1977 edition.  w. fullerton, c3, los alamos scientific lab.
  c
  c compute the log complementary incomplete gamma function for large x
  c and for a .le. x.
  c
        double precision a, x, alx, eps, fk, p, r, s, t, xma, xpa,
       1  d1mach, dlog
        external d1mach
        data eps / 0.d0 /
  c
        if (eps.eq.0.d0) eps = 0.5d0*d1mach(3)
  c
        xpa = x + 1.0d0 - a
        xma = x - 1.d0 - a
  c
        r = 0.d0
        p = 1.d0
        s = p
        do 10 k=1,300
          fk = k
          t = fk*(a-fk)*(1.d0+r)
          r = -t/((xma+2.d0*fk)*(xpa+2.d0*fk)+t)
          p = r*p
          s = s + p
          if (dabs(p).lt.eps*s) go to 20
   10   continue
        call seteru (57hd9lgic  no convergence in 300 terms of continued f
       1raction, 57, 1, 2)
  c
   20   d9lgic = a*alx - x + dlog(s/xpa)
  c
        return
        end