complex(kind(1.d0)) function zcot (z)
      implicit none
c march 1979 edition.  w. fullerton, c3, los alamos scientific lab.
      complex(kind(1.d0)) z
      real(kind(1.d0)) d1mach
      real(kind(1.d0)) eps, xmax, ylarge, ybig, rmin, ymin
      real(kind(1.d0)) x,y,x2,y2,sn2x,den
      integer irold,irold2
      external d1mach
      data eps, xmax, ylarge, ybig, rmin, ymin / 5*0.0d0, 1.5d0 /
c
      if (eps.ne.0.0) go to 10
      eps = d1mach(4)
      xmax = 1.0/eps
      ylarge = -0.5*log(0.5*d1mach(3))
      ybig = -0.5*log(0.5*sqrt(d1mach(3)))
      rmin = exp (max(log(d1mach(1)), -log(d1mach(2))) + 0.01)
c
 10   x = real (z)
      y = aimag (z)
      if (abs(y).gt.ylarge) go to 30
c
      x2 = 2.0*x
      y2 = 2.0*y
      if (abs(x2).gt.xmax) go to 20
      if ( abs(z).lt.rmin) call seteru (55hzcot     abs(z) is zero or so
     1 small that zcot overflows, 55, 5, 2)
c
      call entsrc (irold, 1)
      sn2x = sin(x2)
      call erroff
      den = cosh(y2) - cos(x2)
      call erroff
      call entsrc (irold2, irold)
c
      if (den.lt.x*x2*eps*eps) call seteru (74hzcot    cot is nearly sin
     1gular, x is near a multiple of pi and y is near 0, 74, 3, 2)
      if (den.lt.x*x2*eps .and. abs(x).gt.0.5) call seteru (65hzcot    a
     1nswer is lt half precision, x is near pi and y is near 0, 65, 1,1)
c
      zcot = cmplx (sn2x/den, -sinh(y2)/den, kind(1.d0))
      return
c
 20   if (abs(y).lt.ymin) call seteru (75hzcot    answer would have no p
     1recision, abs(x) is very big and abs(y) small, 75, 4, 2)
      if (abs(y).lt.ybig) call seteru (69hzcot    answer lt half precisi
     1on, abs(x) is very big and abs(y) small, 69, 2, 1)
c
      zcot = cmplx (0.0, 1.0/tanh(y2), kind(1.d0))
      return
c
 30   zcot = cmplx (0.0, sign (1.0d0, y), kind(1.d0))
      return
c
      end