function r9gmic (a, x, alx)
c july 1977 edition.  w. fullerton, c3, los alamos scientific lab.
c
c compute the complementary incomplete gamma function for a near
c a negative integer and for small x.
c
      external alngam, alog, exp, r1mach
      data euler / .5772156649 015329 e0 /
      data eps, bot / 2*0.0 /
c
      if (eps.eq.0.0) eps = 0.5*r1mach(3)
      if (bot.eq.0.0) bot = alog(r1mach(1))
c
      if (a.gt.0.0) call seteru (
     1  41hr9gmic  a must be near a negative integer, 41, 2, 2)
      if (x.le.0.0) call seteru (25hr9gmic  x must be gt zero, 25, 3, 2)
c
      ma = a - 0.5
      fm = -ma
      m = -ma
c
      te = 1.0
      t = 1.0
      s = t
      do 20 k=1,200
        fkp1 = k + 1
        te = -x*te/(fm+fkp1)
        t = te/fkp1
        s = s + t
        if (abs(t).lt.eps*s) go to 30
 20   continue
      call seteru (57hr9gmic  no convergence in 200 terms of continued f
     1raction, 57, 4, 2)
c
 30   r9gmic = -alx - euler + x*s/(fm+1.0)
      if (m.eq.0) return
c
      if (m.eq.1) r9gmic = -r9gmic - 1.0 + 1.0/x
      if (m.eq.1) return
c
      te = fm
      t = 1.0
      s = t
      mm1 = m - 1
      do 40 k=1,mm1
        fk = k
        te = -x*te/fk
        t = te/(fm-fk)
        s = s + t
        if (abs(t).lt.eps*abs(s)) go to 50
 40   continue
c
 50   do 60 k=1,m
        r9gmic = r9gmic + 1.0/float(k)
 60   continue
c
      sgng = 1.0
      if (mod(m,2).eq.1) sgng = -1.0
      alng = alog(r9gmic) - alngam(fm+1.0)
c
      r9gmic = 0.0
      if (alng.gt.bot) r9gmic = sgng*exp(alng)
      if (s.ne.0.0) r9gmic = r9gmic + sign (exp(-fm*alx+alog(abs(s)/fm))
     1  , s)
c
      if (r9gmic.eq.0.0 .and. s.eq.0.0) call seteru (
     1  25hr9gmic  result underflows, 25, 1, 0)
      return
c
      end