lujoin.f

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C*********************************************************************  
    
      SUBROUTINE lujoin(NJOIN,IJOIN)    
    
C...Purpose: to connect a sequence of partons with colour flow indices, 
C...as required for subsequent shower evolution (or other operations).  
      common/lujets/n,k(9000,5),p(9000,5),v(9000,5)
      SAVE /lujets/ 
      common/ludat1/mstu(200),paru(200),mstj(200),parj(200) 
      SAVE /ludat1/ 
      common/ludat2/kchg(500,3),pmas(500,4),parf(2000),vckm(4,4)    
      SAVE /ludat2/ 
      dimension ijoin(*)    
    
C...Check that partons are of right types to be connected.  
      IF(njoin.LT.2) goto 120   
      kqsum=0   
      DO 100 ijn=1,njoin    
      i=ijoin(ijn)  
      IF(i.LE.0.OR.i.GT.n) goto 120 
      IF(k(i,1).LT.1.OR.k(i,1).GT.3) goto 120   
      kc=lucomp(k(i,2)) 
      IF(kc.EQ.0) goto 120  
      kq=kchg(kc,2)*isign(1,k(i,2)) 
      IF(kq.EQ.0) goto 120  
      IF(ijn.NE.1.AND.ijn.NE.njoin.AND.kq.NE.2) goto 120    
      IF(kq.NE.2) kqsum=kqsum+kq    
  100 IF(ijn.EQ.1) kqs=kq   
      IF(kqsum.NE.0) goto 120   
    
C...Connect the partons sequentially (closing for gluon loop).  
      kcs=(9-kqs)/2 
      IF(kqs.EQ.2) kcs=int(4.5+rlu(0))  
      DO 110 ijn=1,njoin    
      i=ijoin(ijn)  
      k(i,1)=3  
      IF(ijn.NE.1) ip=ijoin(ijn-1)  
      IF(ijn.EQ.1) ip=ijoin(njoin)  
      IF(ijn.NE.njoin) in=ijoin(ijn+1)  
      IF(ijn.EQ.njoin) in=ijoin(1)  
      k(i,kcs)=mstu(5)*in   
      k(i,9-kcs)=mstu(5)*ip 
      IF(ijn.EQ.1.AND.kqs.NE.2) k(i,9-kcs)=0    
  110 IF(ijn.EQ.njoin.AND.kqs.NE.2) k(i,kcs)=0  
    
C...Error exit: no action taken.    
      RETURN    
  120 CALL luerrm(12,   
     &'(LUJOIN:) given entries can not be joined by one string')    
    
      RETURN    
      END