dgegv.f

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*> \brief <b> DGEEVX computes the eigenvalues and, optionally, the left and/or right eigenvectors for GE matrices</b>
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
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*> \endhtmlonly
*
*  Definition:
*  ===========
*
*       SUBROUTINE DGEGV( JOBVL, JOBVR, N, A, LDA, B, LDB, ALPHAR, ALPHAI,
*                         BETA, VL, LDVL, VR, LDVR, WORK, LWORK, INFO )
*
*       .. Scalar Arguments ..
*       CHARACTER          JOBVL, JOBVR
*       INTEGER            INFO, LDA, LDB, LDVL, LDVR, LWORK, N
*       ..
*       .. Array Arguments ..
*       DOUBLE PRECISION   A( LDA, * ), ALPHAI( * ), ALPHAR( * ),
*      $                   B( LDB, * ), BETA( * ), VL( LDVL, * ),
*      $                   VR( LDVR, * ), WORK( * )
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> This routine is deprecated and has been replaced by routine DGGEV.
*>
*> DGEGV computes the eigenvalues and, optionally, the left and/or right
*> eigenvectors of a real matrix pair (A,B).
*> Given two square matrices A and B,
*> the generalized nonsymmetric eigenvalue problem (GNEP) is to find the
*> eigenvalues lambda and corresponding (non-zero) eigenvectors x such
*> that
*>
*>    A*x = lambda*B*x.
*>
*> An alternate form is to find the eigenvalues mu and corresponding
*> eigenvectors y such that
*>
*>    mu*A*y = B*y.
*>
*> These two forms are equivalent with mu = 1/lambda and x = y if
*> neither lambda nor mu is zero.  In order to deal with the case that
*> lambda or mu is zero or small, two values alpha and beta are returned
*> for each eigenvalue, such that lambda = alpha/beta and
*> mu = beta/alpha.
*>
*> The vectors x and y in the above equations are right eigenvectors of
*> the matrix pair (A,B).  Vectors u and v satisfying
*>
*>    u**H*A = lambda*u**H*B  or  mu*v**H*A = v**H*B
*>
*> are left eigenvectors of (A,B).
*>
*> Note: this routine performs "full balancing" on A and B
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] JOBVL
*> \verbatim
*>          JOBVL is CHARACTER*1
*>          = 'N':  do not compute the left generalized eigenvectors;
*>          = 'V':  compute the left generalized eigenvectors (returned
*>                  in VL).
*> \endverbatim
*>
*> \param[in] JOBVR
*> \verbatim
*>          JOBVR is CHARACTER*1
*>          = 'N':  do not compute the right generalized eigenvectors;
*>          = 'V':  compute the right generalized eigenvectors (returned
*>                  in VR).
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The order of the matrices A, B, VL, and VR.  N >= 0.
*> \endverbatim
*>
*> \param[in,out] A
*> \verbatim
*>          A is DOUBLE PRECISION array, dimension (LDA, N)
*>          On entry, the matrix A.
*>          If JOBVL = 'V' or JOBVR = 'V', then on exit A
*>          contains the real Schur form of A from the generalized Schur
*>          factorization of the pair (A,B) after balancing.
*>          If no eigenvectors were computed, then only the diagonal
*>          blocks from the Schur form will be correct.  See DGGHRD and
*>          DHGEQZ for details.
*> \endverbatim
*>
*> \param[in] LDA
*> \verbatim
*>          LDA is INTEGER
*>          The leading dimension of A.  LDA >= max(1,N).
*> \endverbatim
*>
*> \param[in,out] B
*> \verbatim
*>          B is DOUBLE PRECISION array, dimension (LDB, N)
*>          On entry, the matrix B.
*>          If JOBVL = 'V' or JOBVR = 'V', then on exit B contains the
*>          upper triangular matrix obtained from B in the generalized
*>          Schur factorization of the pair (A,B) after balancing.
*>          If no eigenvectors were computed, then only those elements of
*>          B corresponding to the diagonal blocks from the Schur form of
*>          A will be correct.  See DGGHRD and DHGEQZ for details.
*> \endverbatim
*>
*> \param[in] LDB
*> \verbatim
*>          LDB is INTEGER
*>          The leading dimension of B.  LDB >= max(1,N).
*> \endverbatim
*>
*> \param[out] ALPHAR
*> \verbatim
*>          ALPHAR is DOUBLE PRECISION array, dimension (N)
*>          The real parts of each scalar alpha defining an eigenvalue of
*>          GNEP.
*> \endverbatim
*>
*> \param[out] ALPHAI
*> \verbatim
*>          ALPHAI is DOUBLE PRECISION array, dimension (N)
*>          The imaginary parts of each scalar alpha defining an
*>          eigenvalue of GNEP.  If ALPHAI(j) is zero, then the j-th
*>          eigenvalue is real; if positive, then the j-th and
*>          (j+1)-st eigenvalues are a complex conjugate pair, with
*>          ALPHAI(j+1) = -ALPHAI(j).
*> \endverbatim
*>
*> \param[out] BETA
*> \verbatim
*>          BETA is DOUBLE PRECISION array, dimension (N)
*>          The scalars beta that define the eigenvalues of GNEP.
*>
*>          Together, the quantities alpha = (ALPHAR(j),ALPHAI(j)) and
*>          beta = BETA(j) represent the j-th eigenvalue of the matrix
*>          pair (A,B), in one of the forms lambda = alpha/beta or
*>          mu = beta/alpha.  Since either lambda or mu may overflow,
*>          they should not, in general, be computed.
*> \endverbatim
*>
*> \param[out] VL
*> \verbatim
*>          VL is DOUBLE PRECISION array, dimension (LDVL,N)
*>          If JOBVL = 'V', the left eigenvectors u(j) are stored
*>          in the columns of VL, in the same order as their eigenvalues.
*>          If the j-th eigenvalue is real, then u(j) = VL(:,j).
*>          If the j-th and (j+1)-st eigenvalues form a complex conjugate
*>          pair, then
*>             u(j) = VL(:,j) + i*VL(:,j+1)
*>          and
*>            u(j+1) = VL(:,j) - i*VL(:,j+1).
*>
*>          Each eigenvector is scaled so that its largest component has
*>          abs(real part) + abs(imag. part) = 1, except for eigenvectors
*>          corresponding to an eigenvalue with alpha = beta = 0, which
*>          are set to zero.
*>          Not referenced if JOBVL = 'N'.
*> \endverbatim
*>
*> \param[in] LDVL
*> \verbatim
*>          LDVL is INTEGER
*>          The leading dimension of the matrix VL. LDVL >= 1, and
*>          if JOBVL = 'V', LDVL >= N.
*> \endverbatim
*>
*> \param[out] VR
*> \verbatim
*>          VR is DOUBLE PRECISION array, dimension (LDVR,N)
*>          If JOBVR = 'V', the right eigenvectors x(j) are stored
*>          in the columns of VR, in the same order as their eigenvalues.
*>          If the j-th eigenvalue is real, then x(j) = VR(:,j).
*>          If the j-th and (j+1)-st eigenvalues form a complex conjugate
*>          pair, then
*>            x(j) = VR(:,j) + i*VR(:,j+1)
*>          and
*>            x(j+1) = VR(:,j) - i*VR(:,j+1).
*>
*>          Each eigenvector is scaled so that its largest component has
*>          abs(real part) + abs(imag. part) = 1, except for eigenvalues
*>          corresponding to an eigenvalue with alpha = beta = 0, which
*>          are set to zero.
*>          Not referenced if JOBVR = 'N'.
*> \endverbatim
*>
*> \param[in] LDVR
*> \verbatim
*>          LDVR is INTEGER
*>          The leading dimension of the matrix VR. LDVR >= 1, and
*>          if JOBVR = 'V', LDVR >= N.
*> \endverbatim
*>
*> \param[out] WORK
*> \verbatim
*>          WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))
*>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
*> \endverbatim
*>
*> \param[in] LWORK
*> \verbatim
*>          LWORK is INTEGER
*>          The dimension of the array WORK.  LWORK >= max(1,8*N).
*>          For good performance, LWORK must generally be larger.
*>          To compute the optimal value of LWORK, call ILAENV to get
*>          blocksizes (for DGEQRF, DORMQR, and DORGQR.)  Then compute:
*>          NB  -- MAX of the blocksizes for DGEQRF, DORMQR, and DORGQR;
*>          The optimal LWORK is:
*>              2*N + MAX( 6*N, N*(NB+1) ).
*>
*>          If LWORK = -1, then a workspace query is assumed; the routine
*>          only calculates the optimal size of the WORK array, returns
*>          this value as the first entry of the WORK array, and no error
*>          message related to LWORK is issued by XERBLA.
*> \endverbatim
*>
*> \param[out] INFO
*> \verbatim
*>          INFO is INTEGER
*>          = 0:  successful exit
*>          < 0:  if INFO = -i, the i-th argument had an illegal value.
*>          = 1,...,N:
*>                The QZ iteration failed.  No eigenvectors have been
*>                calculated, but ALPHAR(j), ALPHAI(j), and BETA(j)
*>                should be correct for j=INFO+1,...,N.
*>          > N:  errors that usually indicate LAPACK problems:
*>                =N+1: error return from DGGBAL
*>                =N+2: error return from DGEQRF
*>                =N+3: error return from DORMQR
*>                =N+4: error return from DORGQR
*>                =N+5: error return from DGGHRD
*>                =N+6: error return from DHGEQZ (other than failed
*>                                                iteration)
*>                =N+7: error return from DTGEVC
*>                =N+8: error return from DGGBAK (computing VL)
*>                =N+9: error return from DGGBAK (computing VR)
*>                =N+10: error return from DLASCL (various calls)
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup doubleGEeigen
*
*> \par Further Details:
*  =====================
*>
*> \verbatim
*>
*>  Balancing
*>  ---------
*>
*>  This driver calls DGGBAL to both permute and scale rows and columns
*>  of A and B.  The permutations PL and PR are chosen so that PL*A*PR
*>  and PL*B*R will be upper triangular except for the diagonal blocks
*>  A(i:j,i:j) and B(i:j,i:j), with i and j as close together as
*>  possible.  The diagonal scaling matrices DL and DR are chosen so
*>  that the pair  DL*PL*A*PR*DR, DL*PL*B*PR*DR have elements close to
*>  one (except for the elements that start out zero.)
*>
*>  After the eigenvalues and eigenvectors of the balanced matrices
*>  have been computed, DGGBAK transforms the eigenvectors back to what
*>  they would have been (in perfect arithmetic) if they had not been
*>  balanced.
*>
*>  Contents of A and B on Exit
*>  -------- -- - --- - -- ----
*>
*>  If any eigenvectors are computed (either JOBVL='V' or JOBVR='V' or
*>  both), then on exit the arrays A and B will contain the real Schur
*>  form[*] of the "balanced" versions of A and B.  If no eigenvectors
*>  are computed, then only the diagonal blocks will be correct.
*>
*>  [*] See DHGEQZ, DGEGS, or read the book "Matrix Computations",
*>      by Golub & van Loan, pub. by Johns Hopkins U. Press.
*> \endverbatim
*>
*  =====================================================================
      SUBROUTINE dgegv( JOBVL, JOBVR, N, A, LDA, B, LDB, ALPHAR, ALPHAI,
     $                  BETA, VL, LDVL, VR, LDVR, WORK, LWORK, INFO )
*
*  -- LAPACK driver routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER          JOBVL, JOBVR
      INTEGER            INFO, LDA, LDB, LDVL, LDVR, LWORK, N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION   A( LDA, * ), ALPHAI( * ), ALPHAR( * ),
     $                   b( ldb, * ), beta( * ), vl( ldvl, * ),
     $                   vr( ldvr, * ), work( * )
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION   ZERO, ONE
      parameter( zero = 0.0d0, one = 1.0d0 )
*     ..
*     .. Local Scalars ..
      LOGICAL            ILIMIT, ILV, ILVL, ILVR, LQUERY
      CHARACTER          CHTEMP
      INTEGER            ICOLS, IHI, IINFO, IJOBVL, IJOBVR, ILEFT, ILO,
     $                   in, iright, irows, itau, iwork, jc, jr, lopt,
     $                   lwkmin, lwkopt, nb, nb1, nb2, nb3
      DOUBLE PRECISION   ABSAI, ABSAR, ABSB, ANRM, ANRM1, ANRM2, BNRM,
     $                   bnrm1, bnrm2, eps, onepls, safmax, safmin,
     $                   salfai, salfar, sbeta, scale, temp
*     ..
*     .. Local Arrays ..
      LOGICAL            LDUMMA( 1 )
*     ..
*     .. External Subroutines ..
      EXTERNAL           dgeqrf, dggbak, dggbal, dgghrd, dhgeqz, dlacpy,
     $                   dlascl, dlaset, dorgqr, dormqr, dtgevc, xerbla
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      INTEGER            ILAENV
      DOUBLE PRECISION   DLAMCH, DLANGE
      EXTERNAL           lsame, ilaenv, dlamch, dlange
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          abs, int, max
*     ..
*     .. Executable Statements ..
*
*     Decode the input arguments
*
      IF( lsame( jobvl, 'N' ) ) THEN
         ijobvl = 1
         ilvl = .false.
      ELSE IF( lsame( jobvl, 'V' ) ) THEN
         ijobvl = 2
         ilvl = .true.
      ELSE
         ijobvl = -1
         ilvl = .false.
      END IF
*
      IF( lsame( jobvr, 'N' ) ) THEN
         ijobvr = 1
         ilvr = .false.
      ELSE IF( lsame( jobvr, 'V' ) ) THEN
         ijobvr = 2
         ilvr = .true.
      ELSE
         ijobvr = -1
         ilvr = .false.
      END IF
      ilv = ilvl .OR. ilvr
*
*     Test the input arguments
*
      lwkmin = max( 8*n, 1 )
      lwkopt = lwkmin
      work( 1 ) = lwkopt
      lquery = ( lwork.EQ.-1 )
      info = 0
      IF( ijobvl.LE.0 ) THEN
         info = -1
      ELSE IF( ijobvr.LE.0 ) THEN
         info = -2
      ELSE IF( n.LT.0 ) THEN
         info = -3
      ELSE IF( lda.LT.max( 1, n ) ) THEN
         info = -5
      ELSE IF( ldb.LT.max( 1, n ) ) THEN
         info = -7
      ELSE IF( ldvl.LT.1 .OR. ( ilvl .AND. ldvl.LT.n ) ) THEN
         info = -12
      ELSE IF( ldvr.LT.1 .OR. ( ilvr .AND. ldvr.LT.n ) ) THEN
         info = -14
      ELSE IF( lwork.LT.lwkmin .AND. .NOT.lquery ) THEN
         info = -16
      END IF
*
      IF( info.EQ.0 ) THEN
         nb1 = ilaenv( 1, 'dgeqrf', ' ', N, N, -1, -1 )
         NB2 = ILAENV( 1, 'dormqr', ' ', N, N, N, -1 )
         NB3 = ILAENV( 1, 'dorgqr', ' ', N, N, N, -1 )
         NB = MAX( NB1, NB2, NB3 )
         LOPT = 2*N + MAX( 6*N, N*( NB+1 ) )
         WORK( 1 ) = LOPT
      END IF
*
.NE.      IF( INFO0 ) THEN
         CALL XERBLA( 'dgegv ', -INFO )
         RETURN
      ELSE IF( LQUERY ) THEN
         RETURN
      END IF
*
*     Quick return if possible
*
.EQ.      IF( N0 )
     $   RETURN
*
*     Get machine constants
*
      EPS = DLAMCH( 'e' )*DLAMCH( 'b' )
      SAFMIN = DLAMCH( 's' )
      SAFMIN = SAFMIN + SAFMIN
      SAFMAX = ONE / SAFMIN
      ONEPLS = ONE + ( 4*EPS )
*
*     Scale A
*
      ANRM = DLANGE( 'm', N, N, A, LDA, WORK )
      ANRM1 = ANRM
      ANRM2 = ONE
.LT.      IF( ANRMONE ) THEN
.LT.         IF( SAFMAX*ANRMONE ) THEN
            ANRM1 = SAFMIN
            ANRM2 = SAFMAX*ANRM
         END IF
      END IF
*
.GT.      IF( ANRMZERO ) THEN
         CALL DLASCL( 'g', -1, -1, ANRM, ONE, N, N, A, LDA, IINFO )
.NE.         IF( IINFO0 ) THEN
            INFO = N + 10
            RETURN
         END IF
      END IF
*
*     Scale B
*
      BNRM = DLANGE( 'm', N, N, B, LDB, WORK )
      BNRM1 = BNRM
      BNRM2 = ONE
.LT.      IF( BNRMONE ) THEN
.LT.         IF( SAFMAX*BNRMONE ) THEN
            BNRM1 = SAFMIN
            BNRM2 = SAFMAX*BNRM
         END IF
      END IF
*
.GT.      IF( BNRMZERO ) THEN
         CALL DLASCL( 'g', -1, -1, BNRM, ONE, N, N, B, LDB, IINFO )
.NE.         IF( IINFO0 ) THEN
            INFO = N + 10
            RETURN
         END IF
      END IF
*
*     Permute the matrix to make it more nearly triangular
*     Workspace layout:  (8*N words -- "work" requires 6*N words)
*        left_permutation, right_permutation, work...
*
      ILEFT = 1
      IRIGHT = N + 1
      IWORK = IRIGHT + N
      CALL DGGBAL( 'p', N, A, LDA, B, LDB, ILO, IHI, WORK( ILEFT ),
     $             WORK( IRIGHT ), WORK( IWORK ), IINFO )
.NE.      IF( IINFO0 ) THEN
         INFO = N + 1
         GO TO 120
      END IF
*
*     Reduce B to triangular form, and initialize VL and/or VR
*     Workspace layout:  ("work..." must have at least N words)
*        left_permutation, right_permutation, tau, work...
*
      IROWS = IHI + 1 - ILO
      IF( ILV ) THEN
         ICOLS = N + 1 - ILO
      ELSE
         ICOLS = IROWS
      END IF
      ITAU = IWORK
      IWORK = ITAU + IROWS
      CALL DGEQRF( IROWS, ICOLS, B( ILO, ILO ), LDB, WORK( ITAU ),
     $             WORK( IWORK ), LWORK+1-IWORK, IINFO )
.GE.      IF( IINFO0 )
     $   LWKOPT = MAX( LWKOPT, INT( WORK( IWORK ) )+IWORK-1 )
.NE.      IF( IINFO0 ) THEN
         INFO = N + 2
         GO TO 120
      END IF
*
      CALL DORMQR( 'l', 't', IROWS, ICOLS, IROWS, B( ILO, ILO ), LDB,
     $             WORK( ITAU ), A( ILO, ILO ), LDA, WORK( IWORK ),
     $             LWORK+1-IWORK, IINFO )
.GE.      IF( IINFO0 )
     $   LWKOPT = MAX( LWKOPT, INT( WORK( IWORK ) )+IWORK-1 )
.NE.      IF( IINFO0 ) THEN
         INFO = N + 3
         GO TO 120
      END IF
*
      IF( ILVL ) THEN
         CALL DLASET( 'full', N, N, ZERO, ONE, VL, LDVL )
         CALL DLACPY( 'l', IROWS-1, IROWS-1, B( ILO+1, ILO ), LDB,
     $                VL( ILO+1, ILO ), LDVL )
         CALL DORGQR( IROWS, IROWS, IROWS, VL( ILO, ILO ), LDVL,
     $                WORK( ITAU ), WORK( IWORK ), LWORK+1-IWORK,
     $                IINFO )
.GE.         IF( IINFO0 )
     $      LWKOPT = MAX( LWKOPT, INT( WORK( IWORK ) )+IWORK-1 )
.NE.         IF( IINFO0 ) THEN
            INFO = N + 4
            GO TO 120
         END IF
      END IF
*
      IF( ILVR )
     $   CALL DLASET( 'full', N, N, ZERO, ONE, VR, LDVR )
*
*     Reduce to generalized Hessenberg form
*
      IF( ILV ) THEN
*
*        Eigenvectors requested -- work on whole matrix.
*
         CALL DGGHRD( JOBVL, JOBVR, N, ILO, IHI, A, LDA, B, LDB, VL,
     $                LDVL, VR, LDVR, IINFO )
      ELSE
         CALL DGGHRD( 'n', 'n', IROWS, 1, IROWS, A( ILO, ILO ), LDA,
     $                B( ILO, ILO ), LDB, VL, LDVL, VR, LDVR, IINFO )
      END IF
.NE.      IF( IINFO0 ) THEN
         INFO = N + 5
         GO TO 120
      END IF
*
*     Perform QZ algorithm
*     Workspace layout:  ("work..." must have at least 1 word)
*        left_permutation, right_permutation, work...
*
      IWORK = ITAU
      IF( ILV ) THEN
         CHTEMP = 's'
      ELSE
         CHTEMP = 'e'
      END IF
      CALL DHGEQZ( CHTEMP, JOBVL, JOBVR, N, ILO, IHI, A, LDA, B, LDB,
     $             ALPHAR, ALPHAI, BETA, VL, LDVL, VR, LDVR,
     $             WORK( IWORK ), LWORK+1-IWORK, IINFO )
.GE.      IF( IINFO0 )
     $   LWKOPT = MAX( LWKOPT, INT( WORK( IWORK ) )+IWORK-1 )
.NE.      IF( IINFO0 ) THEN
.GT..AND..LE.         IF( IINFO0  IINFON ) THEN
            INFO = IINFO
.GT..AND..LE.         ELSE IF( IINFON  IINFO2*N ) THEN
            INFO = IINFO - N
         ELSE
            INFO = N + 6
         END IF
         GO TO 120
      END IF
*
      IF( ILV ) THEN
*
*        Compute Eigenvectors  (DTGEVC requires 6*N words of workspace)
*
         IF( ILVL ) THEN
            IF( ILVR ) THEN
               CHTEMP = 'b'
            ELSE
               CHTEMP = 'l'
            END IF
         ELSE
            CHTEMP = 'r'
         END IF
*
         CALL DTGEVC( CHTEMP, 'b', LDUMMA, N, A, LDA, B, LDB, VL, LDVL,
     $                VR, LDVR, N, IN, WORK( IWORK ), IINFO )
.NE.         IF( IINFO0 ) THEN
            INFO = N + 7
            GO TO 120
         END IF
*
*        Undo balancing on VL and VR, rescale
*
         IF( ILVL ) THEN
            CALL DGGBAK( 'p', 'l', N, ILO, IHI, WORK( ILEFT ),
     $                   WORK( IRIGHT ), N, VL, LDVL, IINFO )
.NE.            IF( IINFO0 ) THEN
               INFO = N + 8
               GO TO 120
            END IF
            DO 50 JC = 1, N
.LT.               IF( ALPHAI( JC )ZERO )
     $            GO TO 50
               TEMP = ZERO
.EQ.               IF( ALPHAI( JC )ZERO ) THEN
                  DO 10 JR = 1, N
                     TEMP = MAX( TEMP, ABS( VL( JR, JC ) ) )
   10             CONTINUE
               ELSE
                  DO 20 JR = 1, N
                     TEMP = MAX( TEMP, ABS( VL( JR, JC ) )+
     $                      ABS( VL( JR, JC+1 ) ) )
   20             CONTINUE
               END IF
.LT.               IF( TEMPSAFMIN )
     $            GO TO 50
               TEMP = ONE / TEMP
.EQ.               IF( ALPHAI( JC )ZERO ) THEN
                  DO 30 JR = 1, N
                     VL( JR, JC ) = VL( JR, JC )*TEMP
   30             CONTINUE
               ELSE
                  DO 40 JR = 1, N
                     VL( JR, JC ) = VL( JR, JC )*TEMP
                     VL( JR, JC+1 ) = VL( JR, JC+1 )*TEMP
   40             CONTINUE
               END IF
   50       CONTINUE
         END IF
         IF( ILVR ) THEN
            CALL DGGBAK( 'p', 'r', N, ILO, IHI, WORK( ILEFT ),
     $                   WORK( IRIGHT ), N, VR, LDVR, IINFO )
.NE.            IF( IINFO0 ) THEN
               INFO = N + 9
               GO TO 120
            END IF
            DO 100 JC = 1, N
.LT.               IF( ALPHAI( JC )ZERO )
     $            GO TO 100
               TEMP = ZERO
.EQ.               IF( ALPHAI( JC )ZERO ) THEN
                  DO 60 JR = 1, N
                     TEMP = MAX( TEMP, ABS( VR( JR, JC ) ) )
   60             CONTINUE
               ELSE
                  DO 70 JR = 1, N
                     TEMP = MAX( TEMP, ABS( VR( JR, JC ) )+
     $                      ABS( VR( JR, JC+1 ) ) )
   70             CONTINUE
               END IF
.LT.               IF( TEMPSAFMIN )
     $            GO TO 100
               TEMP = ONE / TEMP
.EQ.               IF( ALPHAI( JC )ZERO ) THEN
                  DO 80 JR = 1, N
                     VR( JR, JC ) = VR( JR, JC )*TEMP
   80             CONTINUE
               ELSE
                  DO 90 JR = 1, N
                     VR( JR, JC ) = VR( JR, JC )*TEMP
                     VR( JR, JC+1 ) = VR( JR, JC+1 )*TEMP
   90             CONTINUE
               END IF
  100       CONTINUE
         END IF
*
*        End of eigenvector calculation
*
      END IF
*
*     Undo scaling in alpha, beta
*
*     Note: this does not give the alpha and beta for the unscaled
*     problem.
*
*     Un-scaling is limited to avoid underflow in alpha and beta
*     if they are significant.
*
      DO 110 JC = 1, N
         ABSAR = ABS( ALPHAR( JC ) )
         ABSAI = ABS( ALPHAI( JC ) )
         ABSB = ABS( BETA( JC ) )
         SALFAR = ANRM*ALPHAR( JC )
         SALFAI = ANRM*ALPHAI( JC )
         SBETA = BNRM*BETA( JC )
         ILIMIT = .FALSE.
         SCALE = ONE
*
*        Check for significant underflow in ALPHAI
*
.LT..AND..GE.         IF( ABS( SALFAI )SAFMIN  ABSAI
     $       MAX( SAFMIN, EPS*ABSAR, EPS*ABSB ) ) THEN
            ILIMIT = .TRUE.
            SCALE = ( ONEPLS*SAFMIN / ANRM1 ) /
     $              MAX( ONEPLS*SAFMIN, ANRM2*ABSAI )
*
.EQ.         ELSE IF( SALFAIZERO ) THEN
*
*           If insignificant underflow in ALPHAI, then make the
*           conjugate eigenvalue real.
*
.LT..AND..GT.            IF( ALPHAI( JC )ZERO  JC1 ) THEN
               ALPHAI( JC-1 ) = ZERO
.GT..AND..LT.            ELSE IF( ALPHAI( JC )ZERO  JCN ) THEN
               ALPHAI( JC+1 ) = ZERO
            END IF
         END IF
*
*        Check for significant underflow in ALPHAR
*
.LT..AND..GE.         IF( ABS( SALFAR )SAFMIN  ABSAR
     $       MAX( SAFMIN, EPS*ABSAI, EPS*ABSB ) ) THEN
            ILIMIT = .TRUE.
            SCALE = MAX( SCALE, ( ONEPLS*SAFMIN / ANRM1 ) /
     $              MAX( ONEPLS*SAFMIN, ANRM2*ABSAR ) )
         END IF
*
*        Check for significant underflow in BETA
*
.LT..AND..GE.         IF( ABS( SBETA )SAFMIN  ABSB
     $       MAX( SAFMIN, EPS*ABSAR, EPS*ABSAI ) ) THEN
            ILIMIT = .TRUE.
            SCALE = MAX( SCALE, ( ONEPLS*SAFMIN / BNRM1 ) /
     $              MAX( ONEPLS*SAFMIN, BNRM2*ABSB ) )
         END IF
*
*        Check for possible overflow when limiting scaling
*
         IF( ILIMIT ) THEN
            TEMP = ( SCALE*SAFMIN )*MAX( ABS( SALFAR ), ABS( SALFAI ),
     $             ABS( SBETA ) )
.GT.            IF( TEMPONE )
     $         SCALE = SCALE / TEMP
.LT.            IF( SCALEONE )
     $         ILIMIT = .FALSE.
         END IF
*
*        Recompute un-scaled ALPHAR, ALPHAI, BETA if necessary.
*
         IF( ILIMIT ) THEN
            SALFAR = ( SCALE*ALPHAR( JC ) )*ANRM
            SALFAI = ( SCALE*ALPHAI( JC ) )*ANRM
            SBETA = ( SCALE*BETA( JC ) )*BNRM
         END IF
         ALPHAR( JC ) = SALFAR
         ALPHAI( JC ) = SALFAI
         BETA( JC ) = SBETA
  110 CONTINUE
*
  120 CONTINUE
      WORK( 1 ) = LWKOPT
*
      RETURN
*
*     End of DGEGV
*
      END