complex(kind(1.d0)) function ztanh (z)
c april 1977 version.  w. fullerton, c3, los alamos scientific lab.
      complex(kind(1.d0)) z, ci, ztan
      external ztan
      data ci /(0.,1.)/
c
      ztanh = -ci*ztan(ci*z)
c
      return
      end