subroutine beskes (xnu, x, nin, bke)
  c july 1980 edition.   w. fullerton, c3, los alamos scientific lab.
        dimension bke(1)
        external  r1mach
        data alnbig / 0. /
  c
        if (alnbig.eq.0.) alnbig = alog (r1mach(2))
  c
        v = abs(xnu)
        n = iabs(nin)
  c
        if (v.ge.1.) call seteru (29hbeskes  abs(xnu) must be lt 1, 29,
       1  1, 2)
        if (x.le.0.) call seteru (17hbeskes  x is le 0, 17, 2, 2)
        if (n.eq.0) call seteru (
       1  41hbeskes  n the number in the sequence is 0, 41, 3, 2)
  c
        call r9knus (v, x, bke(1), bknu1, iswtch)
        if (n.eq.1) return
  c
        vincr = sign (1.0, float(nin))
        direct = vincr
        if (xnu.ne.0.) direct = vincr*sign(1.0,xnu)
        if (iswtch.eq.1 .and. direct.gt.0.) call seteru (
       1  47hbeskes  x so small bessel k-sub-xnu+1 overflows, 47, 4, 2)
        bke(2) = bknu1
  c
        if (direct.lt.0.) call r9knus (abs(xnu+vincr), x, bke(2), bknu1,
       1  iswtch)
        if (n.eq.2) return
  c
        vend = abs(xnu+float(nin)) - 1.0
        if (x+(vend-0.5)*alog(vend)+.27 - vend*(alog(x)+.306).gt.alnbig)
       1  call seteru (67hbeskes  x so small or abs(nu) so big that bessel
       2 k-sub-nu overflows, 67, 5, 2)
  c
        v = xnu
        do 10 i=3,n
          v = v + vincr
          bke(i) = 2.0*v*bke(i-1)/x + bke(i-2)
   10   continue
  c
        return
        end