File:  [local] / rpl / lapack / lapack / dstevr.f
Revision 1.19: download - view: text, annotated - select for diffs - revision graph
Mon Aug 7 08:39:07 2023 UTC (9 months, 1 week ago) by bertrand
Branches: MAIN
CVS tags: rpl-4_1_35, rpl-4_1_34, HEAD
Première mise à jour de lapack et blas.

    1: *> \brief <b> DSTEVR 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 DSTEVR + dependencies
   10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dstevr.f">
   11: *> [TGZ]</a>
   12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dstevr.f">
   13: *> [ZIP]</a>
   14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dstevr.f">
   15: *> [TXT]</a>
   16: *> \endhtmlonly
   17: *
   18: *  Definition:
   19: *  ===========
   20: *
   21: *       SUBROUTINE DSTEVR( JOBZ, RANGE, N, D, E, VL, VU, IL, IU, ABSTOL,
   22: *                          M, W, Z, LDZ, ISUPPZ, WORK, LWORK, IWORK,
   23: *                          LIWORK, INFO )
   24: *
   25: *       .. Scalar Arguments ..
   26: *       CHARACTER          JOBZ, RANGE
   27: *       INTEGER            IL, INFO, IU, LDZ, LIWORK, LWORK, M, N
   28: *       DOUBLE PRECISION   ABSTOL, VL, VU
   29: *       ..
   30: *       .. Array Arguments ..
   31: *       INTEGER            ISUPPZ( * ), IWORK( * )
   32: *       DOUBLE PRECISION   D( * ), E( * ), W( * ), WORK( * ), Z( LDZ, * )
   33: *       ..
   34: *
   35: *
   36: *> \par Purpose:
   37: *  =============
   38: *>
   39: *> \verbatim
   40: *>
   41: *> DSTEVR computes selected eigenvalues and, optionally, eigenvectors
   42: *> of a real symmetric tridiagonal matrix T.  Eigenvalues and
   43: *> eigenvectors can be selected by specifying either a range of values
   44: *> or a range of indices for the desired eigenvalues.
   45: *>
   46: *> Whenever possible, DSTEVR calls DSTEMR to compute the
   47: *> eigenspectrum using Relatively Robust Representations.  DSTEMR
   48: *> computes eigenvalues by the dqds algorithm, while orthogonal
   49: *> eigenvectors are computed from various "good" L D L^T representations
   50: *> (also known as Relatively Robust Representations). Gram-Schmidt
   51: *> orthogonalization is avoided as far as possible. More specifically,
   52: *> the various steps of the algorithm are as follows. For the i-th
   53: *> unreduced block of T,
   54: *>    (a) Compute T - sigma_i = L_i D_i L_i^T, such that L_i D_i L_i^T
   55: *>         is a relatively robust representation,
   56: *>    (b) Compute the eigenvalues, lambda_j, of L_i D_i L_i^T to high
   57: *>        relative accuracy by the dqds algorithm,
   58: *>    (c) If there is a cluster of close eigenvalues, "choose" sigma_i
   59: *>        close to the cluster, and go to step (a),
   60: *>    (d) Given the approximate eigenvalue lambda_j of L_i D_i L_i^T,
   61: *>        compute the corresponding eigenvector by forming a
   62: *>        rank-revealing twisted factorization.
   63: *> The desired accuracy of the output can be specified by the input
   64: *> parameter ABSTOL.
   65: *>
   66: *> For more details, see "A new O(n^2) algorithm for the symmetric
   67: *> tridiagonal eigenvalue/eigenvector problem", by Inderjit Dhillon,
   68: *> Computer Science Division Technical Report No. UCB//CSD-97-971,
   69: *> UC Berkeley, May 1997.
   70: *>
   71: *>
   72: *> Note 1 : DSTEVR calls DSTEMR when the full spectrum is requested
   73: *> on machines which conform to the ieee-754 floating point standard.
   74: *> DSTEVR calls DSTEBZ and DSTEIN on non-ieee machines and
   75: *> when partial spectrum requests are made.
   76: *>
   77: *> Normal execution of DSTEMR may create NaNs and infinities and
   78: *> hence may abort due to a floating point exception in environments
   79: *> which do not handle NaNs and infinities in the ieee standard default
   80: *> manner.
   81: *> \endverbatim
   82: *
   83: *  Arguments:
   84: *  ==========
   85: *
   86: *> \param[in] JOBZ
   87: *> \verbatim
   88: *>          JOBZ is CHARACTER*1
   89: *>          = 'N':  Compute eigenvalues only;
   90: *>          = 'V':  Compute eigenvalues and eigenvectors.
   91: *> \endverbatim
   92: *>
   93: *> \param[in] RANGE
   94: *> \verbatim
   95: *>          RANGE is CHARACTER*1
   96: *>          = 'A': all eigenvalues will be found.
   97: *>          = 'V': all eigenvalues in the half-open interval (VL,VU]
   98: *>                 will be found.
   99: *>          = 'I': the IL-th through IU-th eigenvalues will be found.
  100: *>          For RANGE = 'V' or 'I' and IU - IL < N - 1, DSTEBZ and
  101: *>          DSTEIN are called
  102: *> \endverbatim
  103: *>
  104: *> \param[in] N
  105: *> \verbatim
  106: *>          N is INTEGER
  107: *>          The order of the matrix.  N >= 0.
  108: *> \endverbatim
  109: *>
  110: *> \param[in,out] D
  111: *> \verbatim
  112: *>          D is DOUBLE PRECISION array, dimension (N)
  113: *>          On entry, the n diagonal elements of the tridiagonal matrix
  114: *>          A.
  115: *>          On exit, D may be multiplied by a constant factor chosen
  116: *>          to avoid over/underflow in computing the eigenvalues.
  117: *> \endverbatim
  118: *>
  119: *> \param[in,out] E
  120: *> \verbatim
  121: *>          E is DOUBLE PRECISION array, dimension (max(1,N-1))
  122: *>          On entry, the (n-1) subdiagonal elements of the tridiagonal
  123: *>          matrix A in elements 1 to N-1 of E.
  124: *>          On exit, E may be multiplied by a constant factor chosen
  125: *>          to avoid over/underflow in computing the eigenvalues.
  126: *> \endverbatim
  127: *>
  128: *> \param[in] VL
  129: *> \verbatim
  130: *>          VL is DOUBLE PRECISION
  131: *>          If RANGE='V', the lower bound 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] VU
  137: *> \verbatim
  138: *>          VU is DOUBLE PRECISION
  139: *>          If RANGE='V', the upper bound of the interval to
  140: *>          be searched for eigenvalues. VL < VU.
  141: *>          Not referenced if RANGE = 'A' or 'I'.
  142: *> \endverbatim
  143: *>
  144: *> \param[in] IL
  145: *> \verbatim
  146: *>          IL is INTEGER
  147: *>          If RANGE='I', the index of the
  148: *>          smallest eigenvalue to be returned.
  149: *>          1 <= IL <= IU <= N, if N > 0; IL = 1 and IU = 0 if N = 0.
  150: *>          Not referenced if RANGE = 'A' or 'V'.
  151: *> \endverbatim
  152: *>
  153: *> \param[in] IU
  154: *> \verbatim
  155: *>          IU is INTEGER
  156: *>          If RANGE='I', the index of the
  157: *>          largest eigenvalue to be returned.
  158: *>          1 <= IL <= IU <= N, if N > 0; IL = 1 and IU = 0 if N = 0.
  159: *>          Not referenced if RANGE = 'A' or 'V'.
  160: *> \endverbatim
  161: *>
  162: *> \param[in] ABSTOL
  163: *> \verbatim
  164: *>          ABSTOL is DOUBLE PRECISION
  165: *>          The absolute error tolerance for the eigenvalues.
  166: *>          An approximate eigenvalue is accepted as converged
  167: *>          when it is determined to lie in an interval [a,b]
  168: *>          of width less than or equal to
  169: *>
  170: *>                  ABSTOL + EPS *   max( |a|,|b| ) ,
  171: *>
  172: *>          where EPS is the machine precision.  If ABSTOL is less than
  173: *>          or equal to zero, then  EPS*|T|  will be used in its place,
  174: *>          where |T| is the 1-norm of the tridiagonal matrix obtained
  175: *>          by reducing A to tridiagonal form.
  176: *>
  177: *>          See "Computing Small Singular Values of Bidiagonal Matrices
  178: *>          with Guaranteed High Relative Accuracy," by Demmel and
  179: *>          Kahan, LAPACK Working Note #3.
  180: *>
  181: *>          If high relative accuracy is important, set ABSTOL to
  182: *>          DLAMCH( 'Safe minimum' ).  Doing so will guarantee that
  183: *>          eigenvalues are computed to high relative accuracy when
  184: *>          possible in future releases.  The current code does not
  185: *>          make any guarantees about high relative accuracy, but
  186: *>          future releases will. See J. Barlow and J. Demmel,
  187: *>          "Computing Accurate Eigensystems of Scaled Diagonally
  188: *>          Dominant Matrices", LAPACK Working Note #7, for a discussion
  189: *>          of which matrices define their eigenvalues to high relative
  190: *>          accuracy.
  191: *> \endverbatim
  192: *>
  193: *> \param[out] M
  194: *> \verbatim
  195: *>          M is INTEGER
  196: *>          The total number of eigenvalues found.  0 <= M <= N.
  197: *>          If RANGE = 'A', M = N, and if RANGE = 'I', M = IU-IL+1.
  198: *> \endverbatim
  199: *>
  200: *> \param[out] W
  201: *> \verbatim
  202: *>          W is DOUBLE PRECISION array, dimension (N)
  203: *>          The first M elements contain the selected eigenvalues in
  204: *>          ascending order.
  205: *> \endverbatim
  206: *>
  207: *> \param[out] Z
  208: *> \verbatim
  209: *>          Z is DOUBLE PRECISION array, dimension (LDZ, max(1,M) )
  210: *>          If JOBZ = 'V', then if INFO = 0, the first M columns of Z
  211: *>          contain the orthonormal eigenvectors of the matrix A
  212: *>          corresponding to the selected eigenvalues, with the i-th
  213: *>          column of Z holding the eigenvector associated with W(i).
  214: *>          Note: the user must ensure that at least max(1,M) columns are
  215: *>          supplied in the array Z; if RANGE = 'V', the exact value of M
  216: *>          is not known in advance and an upper bound must be used.
  217: *> \endverbatim
  218: *>
  219: *> \param[in] LDZ
  220: *> \verbatim
  221: *>          LDZ is INTEGER
  222: *>          The leading dimension of the array Z.  LDZ >= 1, and if
  223: *>          JOBZ = 'V', LDZ >= max(1,N).
  224: *> \endverbatim
  225: *>
  226: *> \param[out] ISUPPZ
  227: *> \verbatim
  228: *>          ISUPPZ is INTEGER array, dimension ( 2*max(1,M) )
  229: *>          The support of the eigenvectors in Z, i.e., the indices
  230: *>          indicating the nonzero elements in Z. The i-th eigenvector
  231: *>          is nonzero only in elements ISUPPZ( 2*i-1 ) through
  232: *>          ISUPPZ( 2*i ).
  233: *>          Implemented only for RANGE = 'A' or 'I' and IU - IL = N - 1
  234: *> \endverbatim
  235: *>
  236: *> \param[out] WORK
  237: *> \verbatim
  238: *>          WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))
  239: *>          On exit, if INFO = 0, WORK(1) returns the optimal (and
  240: *>          minimal) LWORK.
  241: *> \endverbatim
  242: *>
  243: *> \param[in] LWORK
  244: *> \verbatim
  245: *>          LWORK is INTEGER
  246: *>          The dimension of the array WORK.  LWORK >= max(1,20*N).
  247: *>
  248: *>          If LWORK = -1, then a workspace query is assumed; the routine
  249: *>          only calculates the optimal sizes of the WORK and IWORK
  250: *>          arrays, returns these values as the first entries of the WORK
  251: *>          and IWORK arrays, and no error message related to LWORK or
  252: *>          LIWORK is issued by XERBLA.
  253: *> \endverbatim
  254: *>
  255: *> \param[out] IWORK
  256: *> \verbatim
  257: *>          IWORK is INTEGER array, dimension (MAX(1,LIWORK))
  258: *>          On exit, if INFO = 0, IWORK(1) returns the optimal (and
  259: *>          minimal) LIWORK.
  260: *> \endverbatim
  261: *>
  262: *> \param[in] LIWORK
  263: *> \verbatim
  264: *>          LIWORK is INTEGER
  265: *>          The dimension of the array IWORK.  LIWORK >= max(1,10*N).
  266: *>
  267: *>          If LIWORK = -1, then a workspace query is assumed; the
  268: *>          routine only calculates the optimal sizes of the WORK and
  269: *>          IWORK arrays, returns these values as the first entries of
  270: *>          the WORK and IWORK arrays, and no error message related to
  271: *>          LWORK or LIWORK is issued by XERBLA.
  272: *> \endverbatim
  273: *>
  274: *> \param[out] INFO
  275: *> \verbatim
  276: *>          INFO is INTEGER
  277: *>          = 0:  successful exit
  278: *>          < 0:  if INFO = -i, the i-th argument had an illegal value
  279: *>          > 0:  Internal error
  280: *> \endverbatim
  281: *
  282: *  Authors:
  283: *  ========
  284: *
  285: *> \author Univ. of Tennessee
  286: *> \author Univ. of California Berkeley
  287: *> \author Univ. of Colorado Denver
  288: *> \author NAG Ltd.
  289: *
  290: *> \ingroup doubleOTHEReigen
  291: *
  292: *> \par Contributors:
  293: *  ==================
  294: *>
  295: *>     Inderjit Dhillon, IBM Almaden, USA \n
  296: *>     Osni Marques, LBNL/NERSC, USA \n
  297: *>     Ken Stanley, Computer Science Division, University of
  298: *>       California at Berkeley, USA \n
  299: *>
  300: *  =====================================================================
  301:       SUBROUTINE DSTEVR( JOBZ, RANGE, N, D, E, VL, VU, IL, IU, ABSTOL,
  302:      $                   M, W, Z, LDZ, ISUPPZ, WORK, LWORK, IWORK,
  303:      $                   LIWORK, INFO )
  304: *
  305: *  -- LAPACK driver routine --
  306: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
  307: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  308: *
  309: *     .. Scalar Arguments ..
  310:       CHARACTER          JOBZ, RANGE
  311:       INTEGER            IL, INFO, IU, LDZ, LIWORK, LWORK, M, N
  312:       DOUBLE PRECISION   ABSTOL, VL, VU
  313: *     ..
  314: *     .. Array Arguments ..
  315:       INTEGER            ISUPPZ( * ), IWORK( * )
  316:       DOUBLE PRECISION   D( * ), E( * ), W( * ), WORK( * ), Z( LDZ, * )
  317: *     ..
  318: *
  319: *  =====================================================================
  320: *
  321: *     .. Parameters ..
  322:       DOUBLE PRECISION   ZERO, ONE, TWO
  323:       PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0, TWO = 2.0D+0 )
  324: *     ..
  325: *     .. Local Scalars ..
  326:       LOGICAL            ALLEIG, INDEIG, TEST, LQUERY, VALEIG, WANTZ,
  327:      $                   TRYRAC
  328:       CHARACTER          ORDER
  329:       INTEGER            I, IEEEOK, IMAX, INDIBL, INDIFL, INDISP,
  330:      $                   INDIWO, ISCALE, ITMP1, J, JJ, LIWMIN, LWMIN,
  331:      $                   NSPLIT
  332:       DOUBLE PRECISION   BIGNUM, EPS, RMAX, RMIN, SAFMIN, SIGMA, SMLNUM,
  333:      $                   TMP1, TNRM, VLL, VUU
  334: *     ..
  335: *     .. External Functions ..
  336:       LOGICAL            LSAME
  337:       INTEGER            ILAENV
  338:       DOUBLE PRECISION   DLAMCH, DLANST
  339:       EXTERNAL           LSAME, ILAENV, DLAMCH, DLANST
  340: *     ..
  341: *     .. External Subroutines ..
  342:       EXTERNAL           DCOPY, DSCAL, DSTEBZ, DSTEMR, DSTEIN, DSTERF,
  343:      $                   DSWAP, XERBLA
  344: *     ..
  345: *     .. Intrinsic Functions ..
  346:       INTRINSIC          MAX, MIN, SQRT
  347: *     ..
  348: *     .. Executable Statements ..
  349: *
  350: *
  351: *     Test the input parameters.
  352: *
  353:       IEEEOK = ILAENV( 10, 'DSTEVR', 'N', 1, 2, 3, 4 )
  354: *
  355:       WANTZ = LSAME( JOBZ, 'V' )
  356:       ALLEIG = LSAME( RANGE, 'A' )
  357:       VALEIG = LSAME( RANGE, 'V' )
  358:       INDEIG = LSAME( RANGE, 'I' )
  359: *
  360:       LQUERY = ( ( LWORK.EQ.-1 ) .OR. ( LIWORK.EQ.-1 ) )
  361:       LWMIN = MAX( 1, 20*N )
  362:       LIWMIN = MAX( 1, 10*N )
  363: *
  364: *
  365:       INFO = 0
  366:       IF( .NOT.( WANTZ .OR. LSAME( JOBZ, 'N' ) ) ) THEN
  367:          INFO = -1
  368:       ELSE IF( .NOT.( ALLEIG .OR. VALEIG .OR. INDEIG ) ) THEN
  369:          INFO = -2
  370:       ELSE IF( N.LT.0 ) THEN
  371:          INFO = -3
  372:       ELSE
  373:          IF( VALEIG ) THEN
  374:             IF( N.GT.0 .AND. VU.LE.VL )
  375:      $         INFO = -7
  376:          ELSE IF( INDEIG ) THEN
  377:             IF( IL.LT.1 .OR. IL.GT.MAX( 1, N ) ) THEN
  378:                INFO = -8
  379:             ELSE IF( IU.LT.MIN( N, IL ) .OR. IU.GT.N ) THEN
  380:                INFO = -9
  381:             END IF
  382:          END IF
  383:       END IF
  384:       IF( INFO.EQ.0 ) THEN
  385:          IF( LDZ.LT.1 .OR. ( WANTZ .AND. LDZ.LT.N ) ) THEN
  386:             INFO = -14
  387:          END IF
  388:       END IF
  389: *
  390:       IF( INFO.EQ.0 ) THEN
  391:          WORK( 1 ) = LWMIN
  392:          IWORK( 1 ) = LIWMIN
  393: *
  394:          IF( LWORK.LT.LWMIN .AND. .NOT.LQUERY ) THEN
  395:             INFO = -17
  396:          ELSE IF( LIWORK.LT.LIWMIN .AND. .NOT.LQUERY ) THEN
  397:             INFO = -19
  398:          END IF
  399:       END IF
  400: *
  401:       IF( INFO.NE.0 ) THEN
  402:          CALL XERBLA( 'DSTEVR', -INFO )
  403:          RETURN
  404:       ELSE IF( LQUERY ) THEN
  405:          RETURN
  406:       END IF
  407: *
  408: *     Quick return if possible
  409: *
  410:       M = 0
  411:       IF( N.EQ.0 )
  412:      $   RETURN
  413: *
  414:       IF( N.EQ.1 ) THEN
  415:          IF( ALLEIG .OR. INDEIG ) THEN
  416:             M = 1
  417:             W( 1 ) = D( 1 )
  418:          ELSE
  419:             IF( VL.LT.D( 1 ) .AND. VU.GE.D( 1 ) ) THEN
  420:                M = 1
  421:                W( 1 ) = D( 1 )
  422:             END IF
  423:          END IF
  424:          IF( WANTZ )
  425:      $      Z( 1, 1 ) = ONE
  426:          RETURN
  427:       END IF
  428: *
  429: *     Get machine constants.
  430: *
  431:       SAFMIN = DLAMCH( 'Safe minimum' )
  432:       EPS = DLAMCH( 'Precision' )
  433:       SMLNUM = SAFMIN / EPS
  434:       BIGNUM = ONE / SMLNUM
  435:       RMIN = SQRT( SMLNUM )
  436:       RMAX = MIN( SQRT( BIGNUM ), ONE / SQRT( SQRT( SAFMIN ) ) )
  437: *
  438: *
  439: *     Scale matrix to allowable range, if necessary.
  440: *
  441:       ISCALE = 0
  442:       IF( VALEIG ) THEN
  443:          VLL = VL
  444:          VUU = VU
  445:       END IF
  446: *
  447:       TNRM = DLANST( 'M', N, D, E )
  448:       IF( TNRM.GT.ZERO .AND. TNRM.LT.RMIN ) THEN
  449:          ISCALE = 1
  450:          SIGMA = RMIN / TNRM
  451:       ELSE IF( TNRM.GT.RMAX ) THEN
  452:          ISCALE = 1
  453:          SIGMA = RMAX / TNRM
  454:       END IF
  455:       IF( ISCALE.EQ.1 ) THEN
  456:          CALL DSCAL( N, SIGMA, D, 1 )
  457:          CALL DSCAL( N-1, SIGMA, E( 1 ), 1 )
  458:          IF( VALEIG ) THEN
  459:             VLL = VL*SIGMA
  460:             VUU = VU*SIGMA
  461:          END IF
  462:       END IF
  463: 
  464: *     Initialize indices into workspaces.  Note: These indices are used only
  465: *     if DSTERF or DSTEMR fail.
  466: 
  467: *     IWORK(INDIBL:INDIBL+M-1) corresponds to IBLOCK in DSTEBZ and
  468: *     stores the block indices of each of the M<=N eigenvalues.
  469:       INDIBL = 1
  470: *     IWORK(INDISP:INDISP+NSPLIT-1) corresponds to ISPLIT in DSTEBZ and
  471: *     stores the starting and finishing indices of each block.
  472:       INDISP = INDIBL + N
  473: *     IWORK(INDIFL:INDIFL+N-1) stores the indices of eigenvectors
  474: *     that corresponding to eigenvectors that fail to converge in
  475: *     DSTEIN.  This information is discarded; if any fail, the driver
  476: *     returns INFO > 0.
  477:       INDIFL = INDISP + N
  478: *     INDIWO is the offset of the remaining integer workspace.
  479:       INDIWO = INDISP + N
  480: *
  481: *     If all eigenvalues are desired, then
  482: *     call DSTERF or DSTEMR.  If this fails for some eigenvalue, then
  483: *     try DSTEBZ.
  484: *
  485: *
  486:       TEST = .FALSE.
  487:       IF( INDEIG ) THEN
  488:          IF( IL.EQ.1 .AND. IU.EQ.N ) THEN
  489:             TEST = .TRUE.
  490:          END IF
  491:       END IF
  492:       IF( ( ALLEIG .OR. TEST ) .AND. IEEEOK.EQ.1 ) THEN
  493:          CALL DCOPY( N-1, E( 1 ), 1, WORK( 1 ), 1 )
  494:          IF( .NOT.WANTZ ) THEN
  495:             CALL DCOPY( N, D, 1, W, 1 )
  496:             CALL DSTERF( N, W, WORK, INFO )
  497:          ELSE
  498:             CALL DCOPY( N, D, 1, WORK( N+1 ), 1 )
  499:             IF (ABSTOL .LE. TWO*N*EPS) THEN
  500:                TRYRAC = .TRUE.
  501:             ELSE
  502:                TRYRAC = .FALSE.
  503:             END IF
  504:             CALL DSTEMR( JOBZ, 'A', N, WORK( N+1 ), WORK, VL, VU, IL,
  505:      $                   IU, M, W, Z, LDZ, N, ISUPPZ, TRYRAC,
  506:      $                   WORK( 2*N+1 ), LWORK-2*N, IWORK, LIWORK, INFO )
  507: *
  508:          END IF
  509:          IF( INFO.EQ.0 ) THEN
  510:             M = N
  511:             GO TO 10
  512:          END IF
  513:          INFO = 0
  514:       END IF
  515: *
  516: *     Otherwise, call DSTEBZ and, if eigenvectors are desired, DSTEIN.
  517: *
  518:       IF( WANTZ ) THEN
  519:          ORDER = 'B'
  520:       ELSE
  521:          ORDER = 'E'
  522:       END IF
  523: 
  524:       CALL DSTEBZ( RANGE, ORDER, N, VLL, VUU, IL, IU, ABSTOL, D, E, M,
  525:      $             NSPLIT, W, IWORK( INDIBL ), IWORK( INDISP ), WORK,
  526:      $             IWORK( INDIWO ), INFO )
  527: *
  528:       IF( WANTZ ) THEN
  529:          CALL DSTEIN( N, D, E, M, W, IWORK( INDIBL ), IWORK( INDISP ),
  530:      $                Z, LDZ, WORK, IWORK( INDIWO ), IWORK( INDIFL ),
  531:      $                INFO )
  532:       END IF
  533: *
  534: *     If matrix was scaled, then rescale eigenvalues appropriately.
  535: *
  536:    10 CONTINUE
  537:       IF( ISCALE.EQ.1 ) THEN
  538:          IF( INFO.EQ.0 ) THEN
  539:             IMAX = M
  540:          ELSE
  541:             IMAX = INFO - 1
  542:          END IF
  543:          CALL DSCAL( IMAX, ONE / SIGMA, W, 1 )
  544:       END IF
  545: *
  546: *     If eigenvalues are not in order, then sort them, along with
  547: *     eigenvectors.
  548: *
  549:       IF( WANTZ ) THEN
  550:          DO 30 J = 1, M - 1
  551:             I = 0
  552:             TMP1 = W( J )
  553:             DO 20 JJ = J + 1, M
  554:                IF( W( JJ ).LT.TMP1 ) THEN
  555:                   I = JJ
  556:                   TMP1 = W( JJ )
  557:                END IF
  558:    20       CONTINUE
  559: *
  560:             IF( I.NE.0 ) THEN
  561:                ITMP1 = IWORK( I )
  562:                W( I ) = W( J )
  563:                IWORK( I ) = IWORK( J )
  564:                W( J ) = TMP1
  565:                IWORK( J ) = ITMP1
  566:                CALL DSWAP( N, Z( 1, I ), 1, Z( 1, J ), 1 )
  567:             END IF
  568:    30    CONTINUE
  569:       END IF
  570: *
  571: *      Causes problems with tests 19 & 20:
  572: *      IF (wantz .and. INDEIG ) Z( 1,1) = Z(1,1) / 1.002 + .002
  573: *
  574: *
  575:       WORK( 1 ) = LWMIN
  576:       IWORK( 1 ) = LIWMIN
  577:       RETURN
  578: *
  579: *     End of DSTEVR
  580: *
  581:       END

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