function cosdg (x)
  c june 1977 edition.   w. fullerton, c3, los alamos scientific lab.
  c      external cos
        data raddeg / .017453292519943296e0 /
  c
        cosdg = cos (raddeg*x)
  c
        if (amod(x,90.).ne.0.) return
        n = abs(x)/90.0 + 0.5
        n = mod (n, 2)
        if (n.eq.0) cosdg = sign (1.0, cosdg)
        if (n.eq.1) cosdg = 0.0
  c
        return
        end