complex(kind(1.d0)) function zbeta (a, b)
      implicit none
c july 1977 edition.  w. fullerton, c3, los alamos scientific lab.
      complex(kind(1.d0)) a, b, zgamma, zlbeta
      real(kind(1.d0)) xmax,xmin
      external  zgamma, zlbeta
      data xmax / 0.0d0 /
c
      if (xmax.eq.0.0) call d9gaml (xmin, xmax)
c
      if (real(a).le.0.0 .or. real(b).le.0.0) call seteru (
     1  48hzbeta   real part of both arguments must be gt 0, 48, 1, 2)
c
      if (real(a)+real(b).lt.xmax) zbeta = zgamma(a) * (zgamma(b)/
     1  zgamma(a+b) )
      if (real(a)+real(b).lt.xmax) return
c
      zbeta = exp (zlbeta(a, b))
c
      return
      end