complex function clbeta (a, b)
c july 1977 edition.  w. fullerton, c3, los alamos scientific lab.
c a preliminary version that is portable, but not accurate enough.
      complex a, b, clngam
      external clngam
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
      clbeta = clngam(a) + clngam(b) - clngam(a+b)
c
      return
      end