C DEGRE3    SOURCE    CHAT      05/01/12    22:41:03     5004           
      SUBROUTINE DEGRE3(AS0,AS1,AS2,XR1,XI1,XR2,XI2,XR3,XI3)                    
      IMPLICIT INTEGER(I-N)
      IMPLICIT REAL*8(A-H,O-Z)                                                  
-INC CCOPTIO                                                                    
C                                                                               
C                                                                               
C        POLYNOME DE DEGRE 3 SOUS LA FORME                                      
C        X3 + AS2*X2 + AS1*X + AS0 = 0                                          
C                                                                               
C                                                                               
C                                                                               
      TR=SQRT(3.D0)
      Q=AS1/3.D0-AS2*AS2/9.D0
      R=(AS1*AS2-3.D0*AS0)/6.D0-AS2*AS2*AS2/27.D0
      D=Q*Q*Q+R*R                                                               
C
      IF(IIMPI.EQ.9) THEN
        WRITE(6,*) 'Q  ',Q
        WRITE(6,*) 'R  ',R
        WRITE(6,*) 'D  ',D
      ENDIF
C
      IF(D) 1,2,2                                                               
   2  SD=SQRT(D)                                                                
      S1=SIGN(1.D0,R+SD)*((ABS(R+SD))**(1.D0/3.D0))
      S2=SIGN(1.D0,R-SD)*((ABS(R-SD))**(1.D0/3.D0))
      XR1=S1+S2-AS2/3.D0
      XI1=0.D0
      XR2=-(S1+S2)/2.D0-AS2/3.D0
      XI2=TR*(S1-S2)/2.D0
      XR3=XR2                                                                   
      XI3=-XI2                                                                  
      GO TO 3                                                                   
   1  SD=SQRT(-D)                                                               
      RO=(R*R-D)**(1.D0/6.D0)
      ARG=ATAN2(SD,R)/3.D0
      if (abs(arg).lt.1e-7) arg=0.d0
      SOM=RO*COS(ARG)                                                           
      DIF=RO*SIN(ARG)                                                           
      XR1=SOM*2.D0-AS2/3.D0
      XI1=0.D0
      XR2=-SOM   -AS2/3.D0-TR*DIF
      XI2=0.D0
      XR3=-SOM   -AS2/3.D0+TR*DIF
      XI3=0.D0
   3  CONTINUE                                                                  
      RETURN                                                                    
      END