subroutine kin2_v(w,q,m3,m_t,an_eta,E3)

c     this is a program to r* + A ---> meson + A kinametics  
      
c   
c     Liping Gan, Sept 2000

c input: w,q,m3,m_t,an_eta
c output: E3

      
	




       double precision w,q, an_eta,pi
      
      


      double precision m2,m3,m4,m_t,E3,E4,P3
      double precision cal,cbe,cona,conb,conc
     

    


        data pi/3.14159d0/

              
  	m4=m_t
        m2=m_t
        
        cal=(m3*m3+2.0d0*w*m2+w**2-q**2)/(2.0d0*(w+m2))
             
        cbe=q/(w+m2)
        cona=1.0d0-(cbe*dcos(an_eta))**2
        conb=-(2.0d0)*cal*cbe*dcos(an_eta)
        conc=m3*m3-cal**2
        
        P3=(-conb+dsqrt(conb**2-4.0d0*cona*conc))/(2.0d0*cona)
       

        
        E3=dsqrt(P3*P3+m3*m3)
        E4=m2+w-E3
c        if(E4.le.m4)go to 10
c        P4=sqrt(E4*E4-m4*m4)
        
        return
          end