complex function cbeta (a, b)
  c july 1977 edition.  w. fullerton, c3, los alamos scientific lab.
        complex a, b, cexp, cgamma, clbeta
        external  cgamma, clbeta
        data xmax / 0.0 /
  c
        if (xmax.eq.0.0) call r9gaml (xmin, xmax)
  c
        if (real(a).le.0.0 .or. real(b).le.0.0) call seteru (
       1  48hcbeta   real part of both arguments must be gt 0, 48, 1, 2)
  c
        if (real(a)+real(b).lt.xmax) cbeta = cgamma(a) * (cgamma(b)/
       1  cgamma(a+b) )
        if (real(a)+real(b).lt.xmax) return
  c
        cbeta = cexp (clbeta(a, b))
  c
        return
        end