Sources Esope | Cast3M

degre3
C DEGRE3    SOURCE    CB215821  18/09/21    21:15:33     9930           
      SUBROUTINE DEGRE3(AS0,AS1,AS2,XR1,XI1,XR2,XI2,XR3,XI3)
 
      IMPLICIT INTEGER(I-N)
      IMPLICIT REAL*8(A-H,O-Z)
 
 
-INC PPARAM
-INC CCOPTIO
C
C        POLYNOME DE DEGRE 3 SOUS LA FORME
C        X3 + AS2*X2 + AS1*X + AS0 = 0
C
      TR   = SQRT(3.D0)
      AS2S3= AS2 /3.D0
 
 
      Q = AS1/3.D0 - AS2S3**2
      R =(AS1*AS2)/6.D0-AS0/2.D0 - AS2S3**3
      D = Q**3 + R**2
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-AS2S3
      XI1=  0.D0
      XR2=-(S1+S2)/2.D0-AS2S3
      XI2=  TR*(S1-S2)/2.D0
      XR3=  XR2
      XI3= -XI2
      RETURN
 
   1  SD=SQRT(-D)
      RO=(R**2-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-AS2S3
      XI1=0.D0
      XR2=-SOM   -AS2S3 - TR*DIF
      XI2=0.D0
      XR3=-SOM   -AS2S3 + TR*DIF
      XI3=0.D0
 
      RETURN
      END