subroutine dbskes (xnu, x, nin, bke)
c july 1980 edition.   w. fullerton, c3, los alamos scientific lab.
      double precision xnu, x, bke(1), bknu1, v, vincr, vend, alnbig,
     1  d1mach, dlog
      external d1mach, dlog
      data alnbig / 0.d0 /
c
      if (alnbig.eq.0.d0) alnbig = dlog (d1mach(2))
c
      v = dabs(xnu)
      n = iabs(nin)
c
      if (v.ge.1.d0) call seteru (29hdbskes  abs(xnu) must be lt 1, 29,
     1  1, 2)
      if (x.le.0.d0) call seteru (17hdbskes  x is le 0, 17, 2, 2)
      if (n.eq.0) call seteru (
     1  41hdbskes  n the number in the sequence is 0, 41, 3, 2)
c
      call d9knus (v, x, bke(1), bknu1, iswtch)
      if (n.eq.1) return
c
      vincr = sign (1.0, float(nin))
      direct = vincr
      if (xnu.ne.0.d0) direct = vincr*dsign(1.d0, xnu)
      if (iswtch.eq.1 .and. direct.gt.0.) call seteru (
     1  47hdbskes  x so small bessel k-sub-xnu+1 overflows, 47, 4, 2)
      bke(2) = bknu1
c
      if (direct.lt.0.) call d9knus (dabs(xnu+vincr), x, bke(2), bknu1,
     1  iswtch)
      if (n.eq.2) return
c
      vend = dabs (xnu+dble(float(nin))) - 1.0d0
      if (x + (vend-.5d0)*dlog(vend)+0.27d0-vend*(dlog(x)+.306d0)
     1  .gt.alnbig) call seteru (
     2               67hdbskes  x so small or abs(nu) so big that bessel
     3 k-sub-nu overflows, 67, 5, 2)
c
      v = xnu
      do 10 i=3,n
        v = v + vincr
        bke(i) = 2.0d0*v*bke(i-1)/x + bke(i-2)
 10   continue
c
      return
      end