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