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