double precision function dcosdg (x)
  c june 1977 edition.   w. fullerton, c3, los alamos scientific lab.
        double precision x, raddeg, dcos
  c      external dcos
        data raddeg / 0.0174532925 1994329576 9236907684 886 d0 /
  c
        dcosdg = dcos (raddeg*x)
  c
        if (dmod(x,90.d0).ne.0.d0) return
        n = dabs(x)/90.d0 + 0.5d0
        n = mod (n, 2)
        if (n.eq.0) dcosdg = dsign (1.0d0, dcosdg)
        if (n.eq.1) dcosdg = 0.0d0
  c
        return
        end