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