complex(8) function zcbrt (z)
      implicit none
c april 1977 version.  w. fullerton, c3, los alamos scientific lab.
      complex(8) z
      real(8) theta,zarg,r,dcbrt
      external zarg, dcbrt
c
      theta = zarg(z) / 3.0
      r = dcbrt (abs(z))
c
      zcbrt = dcmplx (r*cos(theta), r*sin(theta))
c
      return
      end