subroutine scaleset_m345(p,mu0)
c--- subroutine to calculate dynamic scale equal to
c--- invariant mass of particles 3, 4 and 5
      implicit none
      include 'constants.f'
      include 'process.f'
      double precision p(mxpart,4),mu0

      if((case .eq. 'Wgamma') .or.
     &   (case .eq. 'Zgamma') .or.
     &   (case .eq. 'Wgajet') .or.
     &   (case .eq. 'trigam') .or.
     &   (case .eq. 'Zgajet')) then
        mu0=(p(3,4)+p(4,4)+p(5,4))**2-(p(3,1)+p(4,1)+p(5,1))**2
     &     -(p(3,2)+p(4,2)+p(5,2))**2-(p(3,3)+p(4,3)+p(5,3))**2       
        mu0=dsqrt(dabs(mu0))
      else
        write(6,*) 'dynamicscale m(345) not supported for this process.'
        stop
      endif
      
      return
      end