Sources Esope | Cast3M

jacob2
C JACOB2    SOURCE    FANDEUR   12/03/15    21:26:29     7312
      SUBROUTINE JACOB2(A,D,S)
C=====================================================================
C
C       DIAGONALISATION DE A      SYMETRIQUE
C   ENTREEES
C        A(3,3) = MATRICE A DIAGONALISER  A(1,3)=A(2,3)=0.
C                                         A(3,1)=A(3,2)=0.
C   SORTIES
C        D(3)   =  LES 3 VALEURS PROPRES D(1) > D(2) ET D(3)=A(3,3)
C        S(3,3) =  VECTEURS PROPRES    S(I,3)=0. 0. 1.
C
C        RECUPERATION INCA FEVRIER 85    EBERSOLT
C====================================================================
      IMPLICIT INTEGER(I-N)
      IMPLICIT REAL*8(A-H,O-Z)
C
      DIMENSION A(3,*),D(*),S(3,*)
C
C Valeur particuliere : SQRT(2.)*0.5 = 1/SQRT(2.)
      PARAMETER ( X1sr2 = 0.70710678118654752440084436210484904D0 )
C
      X1  =2.*A(1,2)
      X2  =A(1,1)-A(2,2)
      X3  =SQRT(X2*X2+X1*X1)
      D(1)=0.5*(A(1,1)+A(2,2)+X3)
      D(2)=D(1)-X3
      D(3)=A(3,3)
      S(3,1)=0.
      S(3,2)=0.
      S(1,3)=0.
      S(2,3)=0.
      S(3,3)=1.
C
      IF(X2.EQ.0.)           GOTO 70
      X4=X1/X2
      IF(ABS(X4).LT.1.E+10) GOTO 50
C
  70  CONTINUE
      X5    = X1sr2
      S(1,1)=X5
      S(2,1)=SIGN(X5,X1)
      S(1,2)=-S(2,1)
      S(2,2)=X5
      GOTO 100
C
   50 CONTINUE
      X5=1. + X4*X4
      X5=SIGN(1.D0,X2)/SQRT(X5)
      X6=(1.+X5)*.5
      X6=SQRT(X6)
      X7=(1.-X5)*.5
      X7=SIGN(1.D0,X1)*SQRT(X7)
      S(1,1)= X6
      S(2,1)= X7
      S(1,2)=-X7
      S(2,2)= X6
 100  RETURN
      END