complex(8) function zlbeta (a, b)
        implicit none
  c july 1977 edition.  w. fullerton, c3, los alamos scientific lab.
  c a preliminary version that is portable, but not accurate enough.
        complex(8) a, b, zlngam
        external zlngam
  c
        if (real(a).le.0.0 .or. real(b).le.0.0) call seteru (
       1  48hclbeta  real part of both arguments must be gt 0, 48, 1, 2)
  c
        zlbeta = zlngam(a) + zlngam(b) - zlngam(a+b)
  c
        return
        end