complex function ccbrt (z)
  c april 1977 version.  w. fullerton, c3, los alamos scientific lab.
        complex z
        external  carg, cbrt
  c
        theta = carg(z) / 3.0
        r = cbrt (cabs(z))
  c
        ccbrt = cmplx (r*cos(theta), r*sin(theta))
  c
        return
        end