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

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

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