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