* $Id$
    
C*********************************************************************  
    
      SUBROUTINE LUJMAS_HIJING(PMH,PML)    
    
C...Purpose: to determine, approximately, the two jet masses that   
C...minimize the sum m_H|2 + m_L|2, a la Clavelli and Wyler.    
#include "lujets_hijing.inc"
#include "ludat1_hijing.inc"
#include "ludat2_hijing.inc"
      DIMENSION SM(3,3),SAX(3),PS(3,5)  
    
C...Reset.  
      NP=0  
      DO 110 J1=1,3 
      DO 100 J2=J1,3    
  100 SM(J1,J2)=0.  
      DO 110 J2=1,4 
  110 PS(J1,J2)=0.  
      PSS=0.    
    
C...Take copy of particles that are to be considered in mass analysis.  
      DO 150 I=1,N  
      IF(K(I,1).LE.0.OR.K(I,1).GT.10) GOTO 150  
      IF(MSTU(41).GE.2) THEN    
        KC=LUCOMP_HIJING(K(I,2))   
        IF(KC.EQ.0.OR.KC.EQ.12.OR.KC.EQ.14.OR.KC.EQ.16.OR.  
     &  KC.EQ.18) GOTO 150  
        IF(MSTU(41).GE.3.AND.KCHG(KC,2).EQ.0.AND.LUCHGE_HIJING(K(I,2))
     $       .EQ.0)GOTO 150    
      ENDIF 
      IF(N+NP+1.GE.MSTU(4)-MSTU(32)-5) THEN 
         CALL LUERRM_HIJING(11
     $        ,'(LUJMAS_HIJING:) no more memory left in LUJETS_HIJING')   
        PMH=-2. 
        PML=-2. 
        RETURN  
      ENDIF 
      NP=NP+1   
      DO 120 J=1,5  
  120 P(N+NP,J)=P(I,J)  
      IF(MSTU(42).EQ.0) P(N+NP,5)=0.    
      IF(MSTU(42).EQ.1.AND.K(I,2).NE.22) P(N+NP,5)=PMAS(101,1)  
      P(N+NP,4)=SQRT(P(N+NP,5)**2+P(I,1)**2+P(I,2)**2+P(I,3)**2)    
    
C...Fill information in sphericity tensor and total momentum vector.    
      DO 130 J1=1,3 
      DO 130 J2=J1,3    
  130 SM(J1,J2)=SM(J1,J2)+P(I,J1)*P(I,J2)   
      PSS=PSS+(P(I,1)**2+P(I,2)**2+P(I,3)**2)   
      DO 140 J=1,4  
  140 PS(3,J)=PS(3,J)+P(N+NP,J) 
  150 CONTINUE  
    
C...Very low multiplicities (0 or 1) not considered.    
      IF(NP.LE.1) THEN  
         CALL LUERRM_HIJING(8
     $        ,'(LUJMAS_HIJING:) too few particles for analysis')   
        PMH=-1. 
        PML=-1. 
        RETURN  
      ENDIF 
      PARU(61)=SQRT(MAX(0.,PS(3,4)**2-PS(3,1)**2-PS(3,2)**2-PS(3,3)**2))    
    
C...Find largest eigenvalue to matrix (third degree equation).  
      DO 160 J1=1,3 
      DO 160 J2=J1,3    
  160 SM(J1,J2)=SM(J1,J2)/PSS   
      SQ=(SM(1,1)*SM(2,2)+SM(1,1)*SM(3,3)+SM(2,2)*SM(3,3)-SM(1,2)**2-   
     &SM(1,3)**2-SM(2,3)**2)/3.-1./9.   
      SR=-0.5*(SQ+1./9.+SM(1,1)*SM(2,3)**2+SM(2,2)*SM(1,3)**2+SM(3,3)*  
     &SM(1,2)**2-SM(1,1)*SM(2,2)*SM(3,3))+SM(1,2)*SM(1,3)*SM(2,3)+1./27.    
      SP=COS(ACOS(MAX(MIN(SR/SQRT(-SQ**3),1.),-1.))/3.) 
      SMA=1./3.+SQRT(-SQ)*MAX(2.*SP,SQRT(3.*(1.-SP**2))-SP) 
    
C...Find largest eigenvector by solving equation system.    
      DO 170 J1=1,3 
      SM(J1,J1)=SM(J1,J1)-SMA   
      DO 170 J2=J1+1,3  
  170 SM(J2,J1)=SM(J1,J2)   
      SMAX=0.   
      DO 180 J1=1,3 
      DO 180 J2=1,3 
      IF(ABS(SM(J1,J2)).LE.SMAX) GOTO 180   
      JA=J1 
      JB=J2 
      SMAX=ABS(SM(J1,J2))   
  180 CONTINUE  
      SMAX=0.   
      DO 190 J3=JA+1,JA+2   
      J1=J3-3*((J3-1)/3)    
      RL=SM(J1,JB)/SM(JA,JB)    
      DO 190 J2=1,3 
      SM(J1,J2)=SM(J1,J2)-RL*SM(JA,J2)  
      IF(ABS(SM(J1,J2)).LE.SMAX) GOTO 190   
      JC=J1 
      SMAX=ABS(SM(J1,J2))   
  190 CONTINUE  
      JB1=JB+1-3*(JB/3) 
      JB2=JB+2-3*((JB+1)/3) 
      SAX(JB1)=-SM(JC,JB2)  
      SAX(JB2)=SM(JC,JB1)   
      SAX(JB)=-(SM(JA,JB1)*SAX(JB1)+SM(JA,JB2)*SAX(JB2))/SM(JA,JB)  
    
C...Divide particles into two initial clusters by hemisphere.   
      DO 200 I=N+1,N+NP 
      PSAX=P(I,1)*SAX(1)+P(I,2)*SAX(2)+P(I,3)*SAX(3)    
      IS=1  
      IF(PSAX.LT.0.) IS=2   
      K(I,3)=IS 
      DO 200 J=1,4  
  200 PS(IS,J)=PS(IS,J)+P(I,J)  
      PMS=(PS(1,4)**2-PS(1,1)**2-PS(1,2)**2-PS(1,3)**2)+    
     &(PS(2,4)**2-PS(2,1)**2-PS(2,2)**2-PS(2,3)**2) 
    
C...Reassign one particle at a time; find maximum decrease of m|2 sum.  
  210 PMD=0.    
      IM=0  
      DO 220 J=1,4  
  220 PS(3,J)=PS(1,J)-PS(2,J)   
      DO 230 I=N+1,N+NP 
      PPS=P(I,4)*PS(3,4)-P(I,1)*PS(3,1)-P(I,2)*PS(3,2)-P(I,3)*PS(3,3)   
      IF(K(I,3).EQ.1) PMDI=2.*(P(I,5)**2-PPS)   
      IF(K(I,3).EQ.2) PMDI=2.*(P(I,5)**2+PPS)   
      IF(PMDI.LT.PMD) THEN  
        PMD=PMDI    
        IM=I    
      ENDIF 
  230 CONTINUE  
    
C...Loop back if significant reduction in sum of m|2.   
      IF(PMD.LT.-PARU(48)*PMS) THEN 
        PMS=PMS+PMD 
        IS=K(IM,3)  
        DO 240 J=1,4    
        PS(IS,J)=PS(IS,J)-P(IM,J)   
  240   PS(3-IS,J)=PS(3-IS,J)+P(IM,J)   
        K(IM,3)=3-IS    
        GOTO 210    
      ENDIF 
    
C...Final masses and output.    
      MSTU(61)=N+1  
      MSTU(62)=NP   
      PS(1,5)=SQRT(MAX(0.,PS(1,4)**2-PS(1,1)**2-PS(1,2)**2-PS(1,3)**2)) 
      PS(2,5)=SQRT(MAX(0.,PS(2,4)**2-PS(2,1)**2-PS(2,2)**2-PS(2,3)**2)) 
      PMH=MAX(PS(1,5),PS(2,5))  
      PML=MIN(PS(1,5),PS(2,5))  
    
      RETURN    
      END