C CAL2S2    SOURCE    CHAT      05/01/12    21:45:31     5004           
      SUBROUTINE CAL2S2(NAM,AM,NBM,BM,F3)                                       
      IMPLICIT INTEGER(I-N)
      IMPLICIT REAL*8 (A-H,O-Z)                                                 
      DIMENSION AM(2,*),BM(2,*)
C                                                                               
C     CORDES CROISEES                                                           
      A1B1 = ( BM(1,1)-AM(1,1) )**2 + ( BM(2,1)-AM(2,1) )**2                    
      A2B2 = ( BM(1,2)-AM(1,2) )**2 + ( BM(2,2)-AM(2,2) )**2                    
C     CORDES NON CROISEES                                                       
      A1B2 = ( BM(1,2)-AM(1,1) )**2 + ( BM(2,2)-AM(2,1) )**2                    
      A2B1 = ( BM(1,1)-AM(1,2) )**2 + ( BM(2,1)-AM(2,2) )**2                    
      A1B1 = DSQRT(A1B1)                                                        
      A2B2 = DSQRT(A2B2)                                                        
      A1B2 = DSQRT(A1B2)                                                        
      A2B1 = DSQRT(A2B1)                                                        
      F3 = ( A1B1 + A2B2 - A1B2 - A2B1 ) / 2.                                   
      RETURN                                                                    
      END