complex(kind(1.d0)) function zatanh (z)
      implicit none
c april 1977 version.  w. fullerton, c3, los alamos scientific lab.
      complex(kind(1.d0)) z, ci, zatan
      external zatan
      data ci /(0.,1.)/
c
      zatanh = -ci*zatan(ci*z)
c
      return
      end