Annotation of rpl/lapack/lapack/zhbevx.f, revision 1.8

1.8     ! bertrand    1: *> \brief <b> ZHBEVX computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices</b>
        !             2: *
        !             3: *  =========== DOCUMENTATION ===========
        !             4: *
        !             5: * Online html documentation available at 
        !             6: *            http://www.netlib.org/lapack/explore-html/ 
        !             7: *
        !             8: *> \htmlonly
        !             9: *> Download ZHBEVX + dependencies 
        !            10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/zhbevx.f"> 
        !            11: *> [TGZ]</a> 
        !            12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zhbevx.f"> 
        !            13: *> [ZIP]</a> 
        !            14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zhbevx.f"> 
        !            15: *> [TXT]</a>
        !            16: *> \endhtmlonly 
        !            17: *
        !            18: *  Definition:
        !            19: *  ===========
        !            20: *
        !            21: *       SUBROUTINE ZHBEVX( JOBZ, RANGE, UPLO, N, KD, AB, LDAB, Q, LDQ, VL,
        !            22: *                          VU, IL, IU, ABSTOL, M, W, Z, LDZ, WORK, RWORK,
        !            23: *                          IWORK, IFAIL, INFO )
        !            24: * 
        !            25: *       .. Scalar Arguments ..
        !            26: *       CHARACTER          JOBZ, RANGE, UPLO
        !            27: *       INTEGER            IL, INFO, IU, KD, LDAB, LDQ, LDZ, M, N
        !            28: *       DOUBLE PRECISION   ABSTOL, VL, VU
        !            29: *       ..
        !            30: *       .. Array Arguments ..
        !            31: *       INTEGER            IFAIL( * ), IWORK( * )
        !            32: *       DOUBLE PRECISION   RWORK( * ), W( * )
        !            33: *       COMPLEX*16         AB( LDAB, * ), Q( LDQ, * ), WORK( * ),
        !            34: *      $                   Z( LDZ, * )
        !            35: *       ..
        !            36: *  
        !            37: *
        !            38: *> \par Purpose:
        !            39: *  =============
        !            40: *>
        !            41: *> \verbatim
        !            42: *>
        !            43: *> ZHBEVX computes selected eigenvalues and, optionally, eigenvectors
        !            44: *> of a complex Hermitian band matrix A.  Eigenvalues and eigenvectors
        !            45: *> can be selected by specifying either a range of values or a range of
        !            46: *> indices for the desired eigenvalues.
        !            47: *> \endverbatim
        !            48: *
        !            49: *  Arguments:
        !            50: *  ==========
        !            51: *
        !            52: *> \param[in] JOBZ
        !            53: *> \verbatim
        !            54: *>          JOBZ is CHARACTER*1
        !            55: *>          = 'N':  Compute eigenvalues only;
        !            56: *>          = 'V':  Compute eigenvalues and eigenvectors.
        !            57: *> \endverbatim
        !            58: *>
        !            59: *> \param[in] RANGE
        !            60: *> \verbatim
        !            61: *>          RANGE is CHARACTER*1
        !            62: *>          = 'A': all eigenvalues will be found;
        !            63: *>          = 'V': all eigenvalues in the half-open interval (VL,VU]
        !            64: *>                 will be found;
        !            65: *>          = 'I': the IL-th through IU-th eigenvalues will be found.
        !            66: *> \endverbatim
        !            67: *>
        !            68: *> \param[in] UPLO
        !            69: *> \verbatim
        !            70: *>          UPLO is CHARACTER*1
        !            71: *>          = 'U':  Upper triangle of A is stored;
        !            72: *>          = 'L':  Lower triangle of A is stored.
        !            73: *> \endverbatim
        !            74: *>
        !            75: *> \param[in] N
        !            76: *> \verbatim
        !            77: *>          N is INTEGER
        !            78: *>          The order of the matrix A.  N >= 0.
        !            79: *> \endverbatim
        !            80: *>
        !            81: *> \param[in] KD
        !            82: *> \verbatim
        !            83: *>          KD is INTEGER
        !            84: *>          The number of superdiagonals of the matrix A if UPLO = 'U',
        !            85: *>          or the number of subdiagonals if UPLO = 'L'.  KD >= 0.
        !            86: *> \endverbatim
        !            87: *>
        !            88: *> \param[in,out] AB
        !            89: *> \verbatim
        !            90: *>          AB is COMPLEX*16 array, dimension (LDAB, N)
        !            91: *>          On entry, the upper or lower triangle of the Hermitian band
        !            92: *>          matrix A, stored in the first KD+1 rows of the array.  The
        !            93: *>          j-th column of A is stored in the j-th column of the array AB
        !            94: *>          as follows:
        !            95: *>          if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j;
        !            96: *>          if UPLO = 'L', AB(1+i-j,j)    = A(i,j) for j<=i<=min(n,j+kd).
        !            97: *>
        !            98: *>          On exit, AB is overwritten by values generated during the
        !            99: *>          reduction to tridiagonal form.
        !           100: *> \endverbatim
        !           101: *>
        !           102: *> \param[in] LDAB
        !           103: *> \verbatim
        !           104: *>          LDAB is INTEGER
        !           105: *>          The leading dimension of the array AB.  LDAB >= KD + 1.
        !           106: *> \endverbatim
        !           107: *>
        !           108: *> \param[out] Q
        !           109: *> \verbatim
        !           110: *>          Q is COMPLEX*16 array, dimension (LDQ, N)
        !           111: *>          If JOBZ = 'V', the N-by-N unitary matrix used in the
        !           112: *>                          reduction to tridiagonal form.
        !           113: *>          If JOBZ = 'N', the array Q is not referenced.
        !           114: *> \endverbatim
        !           115: *>
        !           116: *> \param[in] LDQ
        !           117: *> \verbatim
        !           118: *>          LDQ is INTEGER
        !           119: *>          The leading dimension of the array Q.  If JOBZ = 'V', then
        !           120: *>          LDQ >= max(1,N).
        !           121: *> \endverbatim
        !           122: *>
        !           123: *> \param[in] VL
        !           124: *> \verbatim
        !           125: *>          VL is DOUBLE PRECISION
        !           126: *> \endverbatim
        !           127: *>
        !           128: *> \param[in] VU
        !           129: *> \verbatim
        !           130: *>          VU is DOUBLE PRECISION
        !           131: *>          If RANGE='V', the lower and upper bounds of the interval to
        !           132: *>          be searched for eigenvalues. VL < VU.
        !           133: *>          Not referenced if RANGE = 'A' or 'I'.
        !           134: *> \endverbatim
        !           135: *>
        !           136: *> \param[in] IL
        !           137: *> \verbatim
        !           138: *>          IL is INTEGER
        !           139: *> \endverbatim
        !           140: *>
        !           141: *> \param[in] IU
        !           142: *> \verbatim
        !           143: *>          IU is INTEGER
        !           144: *>          If RANGE='I', the indices (in ascending order) of the
        !           145: *>          smallest and largest eigenvalues to be returned.
        !           146: *>          1 <= IL <= IU <= N, if N > 0; IL = 1 and IU = 0 if N = 0.
        !           147: *>          Not referenced if RANGE = 'A' or 'V'.
        !           148: *> \endverbatim
        !           149: *>
        !           150: *> \param[in] ABSTOL
        !           151: *> \verbatim
        !           152: *>          ABSTOL is DOUBLE PRECISION
        !           153: *>          The absolute error tolerance for the eigenvalues.
        !           154: *>          An approximate eigenvalue is accepted as converged
        !           155: *>          when it is determined to lie in an interval [a,b]
        !           156: *>          of width less than or equal to
        !           157: *>
        !           158: *>                  ABSTOL + EPS *   max( |a|,|b| ) ,
        !           159: *>
        !           160: *>          where EPS is the machine precision.  If ABSTOL is less than
        !           161: *>          or equal to zero, then  EPS*|T|  will be used in its place,
        !           162: *>          where |T| is the 1-norm of the tridiagonal matrix obtained
        !           163: *>          by reducing AB to tridiagonal form.
        !           164: *>
        !           165: *>          Eigenvalues will be computed most accurately when ABSTOL is
        !           166: *>          set to twice the underflow threshold 2*DLAMCH('S'), not zero.
        !           167: *>          If this routine returns with INFO>0, indicating that some
        !           168: *>          eigenvectors did not converge, try setting ABSTOL to
        !           169: *>          2*DLAMCH('S').
        !           170: *>
        !           171: *>          See "Computing Small Singular Values of Bidiagonal Matrices
        !           172: *>          with Guaranteed High Relative Accuracy," by Demmel and
        !           173: *>          Kahan, LAPACK Working Note #3.
        !           174: *> \endverbatim
        !           175: *>
        !           176: *> \param[out] M
        !           177: *> \verbatim
        !           178: *>          M is INTEGER
        !           179: *>          The total number of eigenvalues found.  0 <= M <= N.
        !           180: *>          If RANGE = 'A', M = N, and if RANGE = 'I', M = IU-IL+1.
        !           181: *> \endverbatim
        !           182: *>
        !           183: *> \param[out] W
        !           184: *> \verbatim
        !           185: *>          W is DOUBLE PRECISION array, dimension (N)
        !           186: *>          The first M elements contain the selected eigenvalues in
        !           187: *>          ascending order.
        !           188: *> \endverbatim
        !           189: *>
        !           190: *> \param[out] Z
        !           191: *> \verbatim
        !           192: *>          Z is COMPLEX*16 array, dimension (LDZ, max(1,M))
        !           193: *>          If JOBZ = 'V', then if INFO = 0, the first M columns of Z
        !           194: *>          contain the orthonormal eigenvectors of the matrix A
        !           195: *>          corresponding to the selected eigenvalues, with the i-th
        !           196: *>          column of Z holding the eigenvector associated with W(i).
        !           197: *>          If an eigenvector fails to converge, then that column of Z
        !           198: *>          contains the latest approximation to the eigenvector, and the
        !           199: *>          index of the eigenvector is returned in IFAIL.
        !           200: *>          If JOBZ = 'N', then Z is not referenced.
        !           201: *>          Note: the user must ensure that at least max(1,M) columns are
        !           202: *>          supplied in the array Z; if RANGE = 'V', the exact value of M
        !           203: *>          is not known in advance and an upper bound must be used.
        !           204: *> \endverbatim
        !           205: *>
        !           206: *> \param[in] LDZ
        !           207: *> \verbatim
        !           208: *>          LDZ is INTEGER
        !           209: *>          The leading dimension of the array Z.  LDZ >= 1, and if
        !           210: *>          JOBZ = 'V', LDZ >= max(1,N).
        !           211: *> \endverbatim
        !           212: *>
        !           213: *> \param[out] WORK
        !           214: *> \verbatim
        !           215: *>          WORK is COMPLEX*16 array, dimension (N)
        !           216: *> \endverbatim
        !           217: *>
        !           218: *> \param[out] RWORK
        !           219: *> \verbatim
        !           220: *>          RWORK is DOUBLE PRECISION array, dimension (7*N)
        !           221: *> \endverbatim
        !           222: *>
        !           223: *> \param[out] IWORK
        !           224: *> \verbatim
        !           225: *>          IWORK is INTEGER array, dimension (5*N)
        !           226: *> \endverbatim
        !           227: *>
        !           228: *> \param[out] IFAIL
        !           229: *> \verbatim
        !           230: *>          IFAIL is INTEGER array, dimension (N)
        !           231: *>          If JOBZ = 'V', then if INFO = 0, the first M elements of
        !           232: *>          IFAIL are zero.  If INFO > 0, then IFAIL contains the
        !           233: *>          indices of the eigenvectors that failed to converge.
        !           234: *>          If JOBZ = 'N', then IFAIL is not referenced.
        !           235: *> \endverbatim
        !           236: *>
        !           237: *> \param[out] INFO
        !           238: *> \verbatim
        !           239: *>          INFO is INTEGER
        !           240: *>          = 0:  successful exit
        !           241: *>          < 0:  if INFO = -i, the i-th argument had an illegal value
        !           242: *>          > 0:  if INFO = i, then i eigenvectors failed to converge.
        !           243: *>                Their indices are stored in array IFAIL.
        !           244: *> \endverbatim
        !           245: *
        !           246: *  Authors:
        !           247: *  ========
        !           248: *
        !           249: *> \author Univ. of Tennessee 
        !           250: *> \author Univ. of California Berkeley 
        !           251: *> \author Univ. of Colorado Denver 
        !           252: *> \author NAG Ltd. 
        !           253: *
        !           254: *> \date November 2011
        !           255: *
        !           256: *> \ingroup complex16OTHEReigen
        !           257: *
        !           258: *  =====================================================================
1.1       bertrand  259:       SUBROUTINE ZHBEVX( JOBZ, RANGE, UPLO, N, KD, AB, LDAB, Q, LDQ, VL,
                    260:      $                   VU, IL, IU, ABSTOL, M, W, Z, LDZ, WORK, RWORK,
                    261:      $                   IWORK, IFAIL, INFO )
                    262: *
1.8     ! bertrand  263: *  -- LAPACK driver routine (version 3.4.0) --
1.1       bertrand  264: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
                    265: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.8     ! bertrand  266: *     November 2011
1.1       bertrand  267: *
                    268: *     .. Scalar Arguments ..
                    269:       CHARACTER          JOBZ, RANGE, UPLO
                    270:       INTEGER            IL, INFO, IU, KD, LDAB, LDQ, LDZ, M, N
                    271:       DOUBLE PRECISION   ABSTOL, VL, VU
                    272: *     ..
                    273: *     .. Array Arguments ..
                    274:       INTEGER            IFAIL( * ), IWORK( * )
                    275:       DOUBLE PRECISION   RWORK( * ), W( * )
                    276:       COMPLEX*16         AB( LDAB, * ), Q( LDQ, * ), WORK( * ),
                    277:      $                   Z( LDZ, * )
                    278: *     ..
                    279: *
                    280: *  =====================================================================
                    281: *
                    282: *     .. Parameters ..
                    283:       DOUBLE PRECISION   ZERO, ONE
                    284:       PARAMETER          ( ZERO = 0.0D0, ONE = 1.0D0 )
                    285:       COMPLEX*16         CZERO, CONE
                    286:       PARAMETER          ( CZERO = ( 0.0D0, 0.0D0 ),
                    287:      $                   CONE = ( 1.0D0, 0.0D0 ) )
                    288: *     ..
                    289: *     .. Local Scalars ..
                    290:       LOGICAL            ALLEIG, INDEIG, LOWER, TEST, VALEIG, WANTZ
                    291:       CHARACTER          ORDER
                    292:       INTEGER            I, IINFO, IMAX, INDD, INDE, INDEE, INDIBL,
                    293:      $                   INDISP, INDIWK, INDRWK, INDWRK, ISCALE, ITMP1,
                    294:      $                   J, JJ, NSPLIT
                    295:       DOUBLE PRECISION   ABSTLL, ANRM, BIGNUM, EPS, RMAX, RMIN, SAFMIN,
                    296:      $                   SIGMA, SMLNUM, TMP1, VLL, VUU
                    297:       COMPLEX*16         CTMP1
                    298: *     ..
                    299: *     .. External Functions ..
                    300:       LOGICAL            LSAME
                    301:       DOUBLE PRECISION   DLAMCH, ZLANHB
                    302:       EXTERNAL           LSAME, DLAMCH, ZLANHB
                    303: *     ..
                    304: *     .. External Subroutines ..
                    305:       EXTERNAL           DCOPY, DSCAL, DSTEBZ, DSTERF, XERBLA, ZCOPY,
                    306:      $                   ZGEMV, ZHBTRD, ZLACPY, ZLASCL, ZSTEIN, ZSTEQR,
                    307:      $                   ZSWAP
                    308: *     ..
                    309: *     .. Intrinsic Functions ..
                    310:       INTRINSIC          DBLE, MAX, MIN, SQRT
                    311: *     ..
                    312: *     .. Executable Statements ..
                    313: *
                    314: *     Test the input parameters.
                    315: *
                    316:       WANTZ = LSAME( JOBZ, 'V' )
                    317:       ALLEIG = LSAME( RANGE, 'A' )
                    318:       VALEIG = LSAME( RANGE, 'V' )
                    319:       INDEIG = LSAME( RANGE, 'I' )
                    320:       LOWER = LSAME( UPLO, 'L' )
                    321: *
                    322:       INFO = 0
                    323:       IF( .NOT.( WANTZ .OR. LSAME( JOBZ, 'N' ) ) ) THEN
                    324:          INFO = -1
                    325:       ELSE IF( .NOT.( ALLEIG .OR. VALEIG .OR. INDEIG ) ) THEN
                    326:          INFO = -2
                    327:       ELSE IF( .NOT.( LOWER .OR. LSAME( UPLO, 'U' ) ) ) THEN
                    328:          INFO = -3
                    329:       ELSE IF( N.LT.0 ) THEN
                    330:          INFO = -4
                    331:       ELSE IF( KD.LT.0 ) THEN
                    332:          INFO = -5
                    333:       ELSE IF( LDAB.LT.KD+1 ) THEN
                    334:          INFO = -7
                    335:       ELSE IF( WANTZ .AND. LDQ.LT.MAX( 1, N ) ) THEN
                    336:          INFO = -9
                    337:       ELSE
                    338:          IF( VALEIG ) THEN
                    339:             IF( N.GT.0 .AND. VU.LE.VL )
                    340:      $         INFO = -11
                    341:          ELSE IF( INDEIG ) THEN
                    342:             IF( IL.LT.1 .OR. IL.GT.MAX( 1, N ) ) THEN
                    343:                INFO = -12
                    344:             ELSE IF( IU.LT.MIN( N, IL ) .OR. IU.GT.N ) THEN
                    345:                INFO = -13
                    346:             END IF
                    347:          END IF
                    348:       END IF
                    349:       IF( INFO.EQ.0 ) THEN
                    350:          IF( LDZ.LT.1 .OR. ( WANTZ .AND. LDZ.LT.N ) )
                    351:      $      INFO = -18
                    352:       END IF
                    353: *
                    354:       IF( INFO.NE.0 ) THEN
                    355:          CALL XERBLA( 'ZHBEVX', -INFO )
                    356:          RETURN
                    357:       END IF
                    358: *
                    359: *     Quick return if possible
                    360: *
                    361:       M = 0
                    362:       IF( N.EQ.0 )
                    363:      $   RETURN
                    364: *
                    365:       IF( N.EQ.1 ) THEN
                    366:          M = 1
                    367:          IF( LOWER ) THEN
                    368:             CTMP1 = AB( 1, 1 )
                    369:          ELSE
                    370:             CTMP1 = AB( KD+1, 1 )
                    371:          END IF
                    372:          TMP1 = DBLE( CTMP1 )
                    373:          IF( VALEIG ) THEN
                    374:             IF( .NOT.( VL.LT.TMP1 .AND. VU.GE.TMP1 ) )
                    375:      $         M = 0
                    376:          END IF
                    377:          IF( M.EQ.1 ) THEN
                    378:             W( 1 ) = CTMP1
                    379:             IF( WANTZ )
                    380:      $         Z( 1, 1 ) = CONE
                    381:          END IF
                    382:          RETURN
                    383:       END IF
                    384: *
                    385: *     Get machine constants.
                    386: *
                    387:       SAFMIN = DLAMCH( 'Safe minimum' )
                    388:       EPS = DLAMCH( 'Precision' )
                    389:       SMLNUM = SAFMIN / EPS
                    390:       BIGNUM = ONE / SMLNUM
                    391:       RMIN = SQRT( SMLNUM )
                    392:       RMAX = MIN( SQRT( BIGNUM ), ONE / SQRT( SQRT( SAFMIN ) ) )
                    393: *
                    394: *     Scale matrix to allowable range, if necessary.
                    395: *
                    396:       ISCALE = 0
                    397:       ABSTLL = ABSTOL
                    398:       IF( VALEIG ) THEN
                    399:          VLL = VL
                    400:          VUU = VU
                    401:       ELSE
                    402:          VLL = ZERO
                    403:          VUU = ZERO
                    404:       END IF
                    405:       ANRM = ZLANHB( 'M', UPLO, N, KD, AB, LDAB, RWORK )
                    406:       IF( ANRM.GT.ZERO .AND. ANRM.LT.RMIN ) THEN
                    407:          ISCALE = 1
                    408:          SIGMA = RMIN / ANRM
                    409:       ELSE IF( ANRM.GT.RMAX ) THEN
                    410:          ISCALE = 1
                    411:          SIGMA = RMAX / ANRM
                    412:       END IF
                    413:       IF( ISCALE.EQ.1 ) THEN
                    414:          IF( LOWER ) THEN
                    415:             CALL ZLASCL( 'B', KD, KD, ONE, SIGMA, N, N, AB, LDAB, INFO )
                    416:          ELSE
                    417:             CALL ZLASCL( 'Q', KD, KD, ONE, SIGMA, N, N, AB, LDAB, INFO )
                    418:          END IF
                    419:          IF( ABSTOL.GT.0 )
                    420:      $      ABSTLL = ABSTOL*SIGMA
                    421:          IF( VALEIG ) THEN
                    422:             VLL = VL*SIGMA
                    423:             VUU = VU*SIGMA
                    424:          END IF
                    425:       END IF
                    426: *
                    427: *     Call ZHBTRD to reduce Hermitian band matrix to tridiagonal form.
                    428: *
                    429:       INDD = 1
                    430:       INDE = INDD + N
                    431:       INDRWK = INDE + N
                    432:       INDWRK = 1
                    433:       CALL ZHBTRD( JOBZ, UPLO, N, KD, AB, LDAB, RWORK( INDD ),
                    434:      $             RWORK( INDE ), Q, LDQ, WORK( INDWRK ), IINFO )
                    435: *
                    436: *     If all eigenvalues are desired and ABSTOL is less than or equal
                    437: *     to zero, then call DSTERF or ZSTEQR.  If this fails for some
                    438: *     eigenvalue, then try DSTEBZ.
                    439: *
                    440:       TEST = .FALSE.
                    441:       IF (INDEIG) THEN
                    442:          IF (IL.EQ.1 .AND. IU.EQ.N) THEN
                    443:             TEST = .TRUE.
                    444:          END IF
                    445:       END IF
                    446:       IF ((ALLEIG .OR. TEST) .AND. (ABSTOL.LE.ZERO)) THEN
                    447:          CALL DCOPY( N, RWORK( INDD ), 1, W, 1 )
                    448:          INDEE = INDRWK + 2*N
                    449:          IF( .NOT.WANTZ ) THEN
                    450:             CALL DCOPY( N-1, RWORK( INDE ), 1, RWORK( INDEE ), 1 )
                    451:             CALL DSTERF( N, W, RWORK( INDEE ), INFO )
                    452:          ELSE
                    453:             CALL ZLACPY( 'A', N, N, Q, LDQ, Z, LDZ )
                    454:             CALL DCOPY( N-1, RWORK( INDE ), 1, RWORK( INDEE ), 1 )
                    455:             CALL ZSTEQR( JOBZ, N, W, RWORK( INDEE ), Z, LDZ,
                    456:      $                   RWORK( INDRWK ), INFO )
                    457:             IF( INFO.EQ.0 ) THEN
                    458:                DO 10 I = 1, N
                    459:                   IFAIL( I ) = 0
                    460:    10          CONTINUE
                    461:             END IF
                    462:          END IF
                    463:          IF( INFO.EQ.0 ) THEN
                    464:             M = N
                    465:             GO TO 30
                    466:          END IF
                    467:          INFO = 0
                    468:       END IF
                    469: *
                    470: *     Otherwise, call DSTEBZ and, if eigenvectors are desired, ZSTEIN.
                    471: *
                    472:       IF( WANTZ ) THEN
                    473:          ORDER = 'B'
                    474:       ELSE
                    475:          ORDER = 'E'
                    476:       END IF
                    477:       INDIBL = 1
                    478:       INDISP = INDIBL + N
                    479:       INDIWK = INDISP + N
                    480:       CALL DSTEBZ( RANGE, ORDER, N, VLL, VUU, IL, IU, ABSTLL,
                    481:      $             RWORK( INDD ), RWORK( INDE ), M, NSPLIT, W,
                    482:      $             IWORK( INDIBL ), IWORK( INDISP ), RWORK( INDRWK ),
                    483:      $             IWORK( INDIWK ), INFO )
                    484: *
                    485:       IF( WANTZ ) THEN
                    486:          CALL ZSTEIN( N, RWORK( INDD ), RWORK( INDE ), M, W,
                    487:      $                IWORK( INDIBL ), IWORK( INDISP ), Z, LDZ,
                    488:      $                RWORK( INDRWK ), IWORK( INDIWK ), IFAIL, INFO )
                    489: *
                    490: *        Apply unitary matrix used in reduction to tridiagonal
                    491: *        form to eigenvectors returned by ZSTEIN.
                    492: *
                    493:          DO 20 J = 1, M
                    494:             CALL ZCOPY( N, Z( 1, J ), 1, WORK( 1 ), 1 )
                    495:             CALL ZGEMV( 'N', N, N, CONE, Q, LDQ, WORK, 1, CZERO,
                    496:      $                  Z( 1, J ), 1 )
                    497:    20    CONTINUE
                    498:       END IF
                    499: *
                    500: *     If matrix was scaled, then rescale eigenvalues appropriately.
                    501: *
                    502:    30 CONTINUE
                    503:       IF( ISCALE.EQ.1 ) THEN
                    504:          IF( INFO.EQ.0 ) THEN
                    505:             IMAX = M
                    506:          ELSE
                    507:             IMAX = INFO - 1
                    508:          END IF
                    509:          CALL DSCAL( IMAX, ONE / SIGMA, W, 1 )
                    510:       END IF
                    511: *
                    512: *     If eigenvalues are not in order, then sort them, along with
                    513: *     eigenvectors.
                    514: *
                    515:       IF( WANTZ ) THEN
                    516:          DO 50 J = 1, M - 1
                    517:             I = 0
                    518:             TMP1 = W( J )
                    519:             DO 40 JJ = J + 1, M
                    520:                IF( W( JJ ).LT.TMP1 ) THEN
                    521:                   I = JJ
                    522:                   TMP1 = W( JJ )
                    523:                END IF
                    524:    40       CONTINUE
                    525: *
                    526:             IF( I.NE.0 ) THEN
                    527:                ITMP1 = IWORK( INDIBL+I-1 )
                    528:                W( I ) = W( J )
                    529:                IWORK( INDIBL+I-1 ) = IWORK( INDIBL+J-1 )
                    530:                W( J ) = TMP1
                    531:                IWORK( INDIBL+J-1 ) = ITMP1
                    532:                CALL ZSWAP( N, Z( 1, I ), 1, Z( 1, J ), 1 )
                    533:                IF( INFO.NE.0 ) THEN
                    534:                   ITMP1 = IFAIL( I )
                    535:                   IFAIL( I ) = IFAIL( J )
                    536:                   IFAIL( J ) = ITMP1
                    537:                END IF
                    538:             END IF
                    539:    50    CONTINUE
                    540:       END IF
                    541: *
                    542:       RETURN
                    543: *
                    544: *     End of ZHBEVX
                    545: *
                    546:       END

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