complex(kind(1.d0)) function zacos (z)

        implicit none
  c april 1977 version.  w. fullerton, c3, los alamos scientific lab.

        complex(kind(1.d0)) z, zasin
        real(kind(1.d0)) pi2

        external zasin
        data pi2 /1.5707963267 9489661923d0/
  c
        zacos = pi2 - zasin (z)
  c
        return
        end