Annotation of rpl/lapack/lapack/dsygvx.f, revision 1.11

1.10      bertrand    1: *> \brief \b DSYGST
                      2: *
                      3: *  =========== DOCUMENTATION ===========
                      4: *
                      5: * Online html documentation available at 
                      6: *            http://www.netlib.org/lapack/explore-html/ 
                      7: *
                      8: *> \htmlonly
                      9: *> Download DSYGVX + dependencies 
                     10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dsygvx.f"> 
                     11: *> [TGZ]</a> 
                     12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dsygvx.f"> 
                     13: *> [ZIP]</a> 
                     14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dsygvx.f"> 
                     15: *> [TXT]</a>
                     16: *> \endhtmlonly 
                     17: *
                     18: *  Definition:
                     19: *  ===========
                     20: *
                     21: *       SUBROUTINE DSYGVX( ITYPE, JOBZ, RANGE, UPLO, N, A, LDA, B, LDB,
                     22: *                          VL, VU, IL, IU, ABSTOL, M, W, Z, LDZ, WORK,
                     23: *                          LWORK, IWORK, IFAIL, INFO )
                     24: * 
                     25: *       .. Scalar Arguments ..
                     26: *       CHARACTER          JOBZ, RANGE, UPLO
                     27: *       INTEGER            IL, INFO, ITYPE, IU, LDA, LDB, LDZ, LWORK, M, N
                     28: *       DOUBLE PRECISION   ABSTOL, VL, VU
                     29: *       ..
                     30: *       .. Array Arguments ..
                     31: *       INTEGER            IFAIL( * ), IWORK( * )
                     32: *       DOUBLE PRECISION   A( LDA, * ), B( LDB, * ), W( * ), WORK( * ),
                     33: *      $                   Z( LDZ, * )
                     34: *       ..
                     35: *  
                     36: *
                     37: *> \par Purpose:
                     38: *  =============
                     39: *>
                     40: *> \verbatim
                     41: *>
                     42: *> DSYGVX computes selected eigenvalues, and optionally, eigenvectors
                     43: *> of a real generalized symmetric-definite eigenproblem, of the form
                     44: *> A*x=(lambda)*B*x,  A*Bx=(lambda)*x,  or B*A*x=(lambda)*x.  Here A
                     45: *> and B are assumed to be symmetric and B is also positive definite.
                     46: *> Eigenvalues and eigenvectors can be selected by specifying either a
                     47: *> range of values or a range of indices for the desired eigenvalues.
                     48: *> \endverbatim
                     49: *
                     50: *  Arguments:
                     51: *  ==========
                     52: *
                     53: *> \param[in] ITYPE
                     54: *> \verbatim
                     55: *>          ITYPE is INTEGER
                     56: *>          Specifies the problem type to be solved:
                     57: *>          = 1:  A*x = (lambda)*B*x
                     58: *>          = 2:  A*B*x = (lambda)*x
                     59: *>          = 3:  B*A*x = (lambda)*x
                     60: *> \endverbatim
                     61: *>
                     62: *> \param[in] JOBZ
                     63: *> \verbatim
                     64: *>          JOBZ is CHARACTER*1
                     65: *>          = 'N':  Compute eigenvalues only;
                     66: *>          = 'V':  Compute eigenvalues and eigenvectors.
                     67: *> \endverbatim
                     68: *>
                     69: *> \param[in] RANGE
                     70: *> \verbatim
                     71: *>          RANGE is CHARACTER*1
                     72: *>          = 'A': all eigenvalues will be found.
                     73: *>          = 'V': all eigenvalues in the half-open interval (VL,VU]
                     74: *>                 will be found.
                     75: *>          = 'I': the IL-th through IU-th eigenvalues will be found.
                     76: *> \endverbatim
                     77: *>
                     78: *> \param[in] UPLO
                     79: *> \verbatim
                     80: *>          UPLO is CHARACTER*1
                     81: *>          = 'U':  Upper triangle of A and B are stored;
                     82: *>          = 'L':  Lower triangle of A and B are stored.
                     83: *> \endverbatim
                     84: *>
                     85: *> \param[in] N
                     86: *> \verbatim
                     87: *>          N is INTEGER
                     88: *>          The order of the matrix pencil (A,B).  N >= 0.
                     89: *> \endverbatim
                     90: *>
                     91: *> \param[in,out] A
                     92: *> \verbatim
                     93: *>          A is DOUBLE PRECISION array, dimension (LDA, N)
                     94: *>          On entry, the symmetric matrix A.  If UPLO = 'U', the
                     95: *>          leading N-by-N upper triangular part of A contains the
                     96: *>          upper triangular part of the matrix A.  If UPLO = 'L',
                     97: *>          the leading N-by-N lower triangular part of A contains
                     98: *>          the lower triangular part of the matrix A.
                     99: *>
                    100: *>          On exit, the lower triangle (if UPLO='L') or the upper
                    101: *>          triangle (if UPLO='U') of A, including the diagonal, is
                    102: *>          destroyed.
                    103: *> \endverbatim
                    104: *>
                    105: *> \param[in] LDA
                    106: *> \verbatim
                    107: *>          LDA is INTEGER
                    108: *>          The leading dimension of the array A.  LDA >= max(1,N).
                    109: *> \endverbatim
                    110: *>
                    111: *> \param[in,out] B
                    112: *> \verbatim
                    113: *>          B is DOUBLE PRECISION array, dimension (LDB, N)
                    114: *>          On entry, the symmetric matrix B.  If UPLO = 'U', the
                    115: *>          leading N-by-N upper triangular part of B contains the
                    116: *>          upper triangular part of the matrix B.  If UPLO = 'L',
                    117: *>          the leading N-by-N lower triangular part of B contains
                    118: *>          the lower triangular part of the matrix B.
                    119: *>
                    120: *>          On exit, if INFO <= N, the part of B containing the matrix is
                    121: *>          overwritten by the triangular factor U or L from the Cholesky
                    122: *>          factorization B = U**T*U or B = L*L**T.
                    123: *> \endverbatim
                    124: *>
                    125: *> \param[in] LDB
                    126: *> \verbatim
                    127: *>          LDB is INTEGER
                    128: *>          The leading dimension of the array B.  LDB >= max(1,N).
                    129: *> \endverbatim
                    130: *>
                    131: *> \param[in] VL
                    132: *> \verbatim
                    133: *>          VL is DOUBLE PRECISION
                    134: *> \endverbatim
                    135: *>
                    136: *> \param[in] VU
                    137: *> \verbatim
                    138: *>          VU is DOUBLE PRECISION
                    139: *>          If RANGE='V', the lower and upper bounds 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: *> \endverbatim
                    148: *>
                    149: *> \param[in] IU
                    150: *> \verbatim
                    151: *>          IU is INTEGER
                    152: *>          If RANGE='I', the indices (in ascending order) of the
                    153: *>          smallest and largest eigenvalues to be returned.
                    154: *>          1 <= IL <= IU <= N, if N > 0; IL = 1 and IU = 0 if N = 0.
                    155: *>          Not referenced if RANGE = 'A' or 'V'.
                    156: *> \endverbatim
                    157: *>
                    158: *> \param[in] ABSTOL
                    159: *> \verbatim
                    160: *>          ABSTOL is DOUBLE PRECISION
                    161: *>          The absolute error tolerance for the eigenvalues.
                    162: *>          An approximate eigenvalue is accepted as converged
                    163: *>          when it is determined to lie in an interval [a,b]
                    164: *>          of width less than or equal to
                    165: *>
                    166: *>                  ABSTOL + EPS *   max( |a|,|b| ) ,
                    167: *>
                    168: *>          where EPS is the machine precision.  If ABSTOL is less than
                    169: *>          or equal to zero, then  EPS*|T|  will be used in its place,
                    170: *>          where |T| is the 1-norm of the tridiagonal matrix obtained
                    171: *>          by reducing C to tridiagonal form, where C is the symmetric
                    172: *>          matrix of the standard symmetric problem to which the
                    173: *>          generalized problem is transformed.
                    174: *>
                    175: *>          Eigenvalues will be computed most accurately when ABSTOL is
                    176: *>          set to twice the underflow threshold 2*DLAMCH('S'), not zero.
                    177: *>          If this routine returns with INFO>0, indicating that some
                    178: *>          eigenvectors did not converge, try setting ABSTOL to
                    179: *>          2*DLAMCH('S').
                    180: *> \endverbatim
                    181: *>
                    182: *> \param[out] M
                    183: *> \verbatim
                    184: *>          M is INTEGER
                    185: *>          The total number of eigenvalues found.  0 <= M <= N.
                    186: *>          If RANGE = 'A', M = N, and if RANGE = 'I', M = IU-IL+1.
                    187: *> \endverbatim
                    188: *>
                    189: *> \param[out] W
                    190: *> \verbatim
                    191: *>          W is DOUBLE PRECISION array, dimension (N)
                    192: *>          On normal exit, the first M elements contain the selected
                    193: *>          eigenvalues in ascending order.
                    194: *> \endverbatim
                    195: *>
                    196: *> \param[out] Z
                    197: *> \verbatim
                    198: *>          Z is DOUBLE PRECISION array, dimension (LDZ, max(1,M))
                    199: *>          If JOBZ = 'N', then Z is not referenced.
                    200: *>          If JOBZ = 'V', then if INFO = 0, the first M columns of Z
                    201: *>          contain the orthonormal eigenvectors of the matrix A
                    202: *>          corresponding to the selected eigenvalues, with the i-th
                    203: *>          column of Z holding the eigenvector associated with W(i).
                    204: *>          The eigenvectors are normalized as follows:
                    205: *>          if ITYPE = 1 or 2, Z**T*B*Z = I;
                    206: *>          if ITYPE = 3, Z**T*inv(B)*Z = I.
                    207: *>
                    208: *>          If an eigenvector fails to converge, then that column of Z
                    209: *>          contains the latest approximation to the eigenvector, and the
                    210: *>          index of the eigenvector is returned in IFAIL.
                    211: *>          Note: the user must ensure that at least max(1,M) columns are
                    212: *>          supplied in the array Z; if RANGE = 'V', the exact value of M
                    213: *>          is not known in advance and an upper bound must be used.
                    214: *> \endverbatim
                    215: *>
                    216: *> \param[in] LDZ
                    217: *> \verbatim
                    218: *>          LDZ is INTEGER
                    219: *>          The leading dimension of the array Z.  LDZ >= 1, and if
                    220: *>          JOBZ = 'V', LDZ >= max(1,N).
                    221: *> \endverbatim
                    222: *>
                    223: *> \param[out] WORK
                    224: *> \verbatim
                    225: *>          WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))
                    226: *>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
                    227: *> \endverbatim
                    228: *>
                    229: *> \param[in] LWORK
                    230: *> \verbatim
                    231: *>          LWORK is INTEGER
                    232: *>          The length of the array WORK.  LWORK >= max(1,8*N).
                    233: *>          For optimal efficiency, LWORK >= (NB+3)*N,
                    234: *>          where NB is the blocksize for DSYTRD returned by ILAENV.
                    235: *>
                    236: *>          If LWORK = -1, then a workspace query is assumed; the routine
                    237: *>          only calculates the optimal size of the WORK array, returns
                    238: *>          this value as the first entry of the WORK array, and no error
                    239: *>          message related to LWORK is issued by XERBLA.
                    240: *> \endverbatim
                    241: *>
                    242: *> \param[out] IWORK
                    243: *> \verbatim
                    244: *>          IWORK is INTEGER array, dimension (5*N)
                    245: *> \endverbatim
                    246: *>
                    247: *> \param[out] IFAIL
                    248: *> \verbatim
                    249: *>          IFAIL is INTEGER array, dimension (N)
                    250: *>          If JOBZ = 'V', then if INFO = 0, the first M elements of
                    251: *>          IFAIL are zero.  If INFO > 0, then IFAIL contains the
                    252: *>          indices of the eigenvectors that failed to converge.
                    253: *>          If JOBZ = 'N', then IFAIL is not referenced.
                    254: *> \endverbatim
                    255: *>
                    256: *> \param[out] INFO
                    257: *> \verbatim
                    258: *>          INFO is INTEGER
                    259: *>          = 0:  successful exit
                    260: *>          < 0:  if INFO = -i, the i-th argument had an illegal value
                    261: *>          > 0:  DPOTRF or DSYEVX returned an error code:
                    262: *>             <= N:  if INFO = i, DSYEVX failed to converge;
                    263: *>                    i eigenvectors failed to converge.  Their indices
                    264: *>                    are stored in array IFAIL.
                    265: *>             > N:   if INFO = N + i, for 1 <= i <= N, then the leading
                    266: *>                    minor of order i of B is not positive definite.
                    267: *>                    The factorization of B could not be completed and
                    268: *>                    no eigenvalues or eigenvectors were computed.
                    269: *> \endverbatim
                    270: *
                    271: *  Authors:
                    272: *  ========
                    273: *
                    274: *> \author Univ. of Tennessee 
                    275: *> \author Univ. of California Berkeley 
                    276: *> \author Univ. of Colorado Denver 
                    277: *> \author NAG Ltd. 
                    278: *
                    279: *> \date November 2011
                    280: *
                    281: *> \ingroup doubleSYeigen
                    282: *
                    283: *> \par Contributors:
                    284: *  ==================
                    285: *>
                    286: *>     Mark Fahey, Department of Mathematics, Univ. of Kentucky, USA
                    287: *
                    288: *  =====================================================================
1.1       bertrand  289:       SUBROUTINE DSYGVX( ITYPE, JOBZ, RANGE, UPLO, N, A, LDA, B, LDB,
                    290:      $                   VL, VU, IL, IU, ABSTOL, M, W, Z, LDZ, WORK,
                    291:      $                   LWORK, IWORK, IFAIL, INFO )
                    292: *
1.10      bertrand  293: *  -- LAPACK driver routine (version 3.4.0) --
1.1       bertrand  294: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
                    295: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.10      bertrand  296: *     November 2011
1.1       bertrand  297: *
                    298: *     .. Scalar Arguments ..
                    299:       CHARACTER          JOBZ, RANGE, UPLO
                    300:       INTEGER            IL, INFO, ITYPE, IU, LDA, LDB, LDZ, LWORK, M, N
                    301:       DOUBLE PRECISION   ABSTOL, VL, VU
                    302: *     ..
                    303: *     .. Array Arguments ..
                    304:       INTEGER            IFAIL( * ), IWORK( * )
                    305:       DOUBLE PRECISION   A( LDA, * ), B( LDB, * ), W( * ), WORK( * ),
                    306:      $                   Z( LDZ, * )
                    307: *     ..
                    308: *
                    309: * =====================================================================
                    310: *
                    311: *     .. Parameters ..
                    312:       DOUBLE PRECISION   ONE
                    313:       PARAMETER          ( ONE = 1.0D+0 )
                    314: *     ..
                    315: *     .. Local Scalars ..
                    316:       LOGICAL            ALLEIG, INDEIG, LQUERY, UPPER, VALEIG, WANTZ
                    317:       CHARACTER          TRANS
                    318:       INTEGER            LWKMIN, LWKOPT, NB
                    319: *     ..
                    320: *     .. External Functions ..
                    321:       LOGICAL            LSAME
                    322:       INTEGER            ILAENV
                    323:       EXTERNAL           LSAME, ILAENV
                    324: *     ..
                    325: *     .. External Subroutines ..
                    326:       EXTERNAL           DPOTRF, DSYEVX, DSYGST, DTRMM, DTRSM, XERBLA
                    327: *     ..
                    328: *     .. Intrinsic Functions ..
                    329:       INTRINSIC          MAX, MIN
                    330: *     ..
                    331: *     .. Executable Statements ..
                    332: *
                    333: *     Test the input parameters.
                    334: *
                    335:       UPPER = LSAME( UPLO, 'U' )
                    336:       WANTZ = LSAME( JOBZ, 'V' )
                    337:       ALLEIG = LSAME( RANGE, 'A' )
                    338:       VALEIG = LSAME( RANGE, 'V' )
                    339:       INDEIG = LSAME( RANGE, 'I' )
                    340:       LQUERY = ( LWORK.EQ.-1 )
                    341: *
                    342:       INFO = 0
                    343:       IF( ITYPE.LT.1 .OR. ITYPE.GT.3 ) THEN
                    344:          INFO = -1
                    345:       ELSE IF( .NOT.( WANTZ .OR. LSAME( JOBZ, 'N' ) ) ) THEN
                    346:          INFO = -2
                    347:       ELSE IF( .NOT.( ALLEIG .OR. VALEIG .OR. INDEIG ) ) THEN
                    348:          INFO = -3
                    349:       ELSE IF( .NOT.( UPPER .OR. LSAME( UPLO, 'L' ) ) ) THEN
                    350:          INFO = -4
                    351:       ELSE IF( N.LT.0 ) THEN
                    352:          INFO = -5
                    353:       ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
                    354:          INFO = -7
                    355:       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
                    356:          INFO = -9
                    357:       ELSE
                    358:          IF( VALEIG ) THEN
                    359:             IF( N.GT.0 .AND. VU.LE.VL )
                    360:      $         INFO = -11
                    361:          ELSE IF( INDEIG ) THEN
                    362:             IF( IL.LT.1 .OR. IL.GT.MAX( 1, N ) ) THEN
                    363:                INFO = -12
                    364:             ELSE IF( IU.LT.MIN( N, IL ) .OR. IU.GT.N ) THEN
                    365:                INFO = -13
                    366:             END IF
                    367:          END IF
                    368:       END IF
                    369:       IF (INFO.EQ.0) THEN
                    370:          IF (LDZ.LT.1 .OR. (WANTZ .AND. LDZ.LT.N)) THEN
                    371:             INFO = -18
                    372:          END IF
                    373:       END IF
                    374: *
                    375:       IF( INFO.EQ.0 ) THEN
                    376:          LWKMIN = MAX( 1, 8*N )
                    377:          NB = ILAENV( 1, 'DSYTRD', UPLO, N, -1, -1, -1 )
                    378:          LWKOPT = MAX( LWKMIN, ( NB + 3 )*N )
                    379:          WORK( 1 ) = LWKOPT
                    380: *
                    381:          IF( LWORK.LT.LWKMIN .AND. .NOT.LQUERY ) THEN
                    382:             INFO = -20
                    383:          END IF
                    384:       END IF
                    385: *
                    386:       IF( INFO.NE.0 ) THEN
                    387:          CALL XERBLA( 'DSYGVX', -INFO )
                    388:          RETURN
                    389:       ELSE IF( LQUERY ) THEN
                    390:          RETURN
                    391:       END IF
                    392: *
                    393: *     Quick return if possible
                    394: *
                    395:       M = 0
                    396:       IF( N.EQ.0 ) THEN
                    397:          RETURN
                    398:       END IF
                    399: *
                    400: *     Form a Cholesky factorization of B.
                    401: *
                    402:       CALL DPOTRF( UPLO, N, B, LDB, INFO )
                    403:       IF( INFO.NE.0 ) THEN
                    404:          INFO = N + INFO
                    405:          RETURN
                    406:       END IF
                    407: *
                    408: *     Transform problem to standard eigenvalue problem and solve.
                    409: *
                    410:       CALL DSYGST( ITYPE, UPLO, N, A, LDA, B, LDB, INFO )
                    411:       CALL DSYEVX( JOBZ, RANGE, UPLO, N, A, LDA, VL, VU, IL, IU, ABSTOL,
                    412:      $             M, W, Z, LDZ, WORK, LWORK, IWORK, IFAIL, INFO )
                    413: *
                    414:       IF( WANTZ ) THEN
                    415: *
                    416: *        Backtransform eigenvectors to the original problem.
                    417: *
                    418:          IF( INFO.GT.0 )
                    419:      $      M = INFO - 1
                    420:          IF( ITYPE.EQ.1 .OR. ITYPE.EQ.2 ) THEN
                    421: *
                    422: *           For A*x=(lambda)*B*x and A*B*x=(lambda)*x;
1.9       bertrand  423: *           backtransform eigenvectors: x = inv(L)**T*y or inv(U)*y
1.1       bertrand  424: *
                    425:             IF( UPPER ) THEN
                    426:                TRANS = 'N'
                    427:             ELSE
                    428:                TRANS = 'T'
                    429:             END IF
                    430: *
                    431:             CALL DTRSM( 'Left', UPLO, TRANS, 'Non-unit', N, M, ONE, B,
                    432:      $                  LDB, Z, LDZ )
                    433: *
                    434:          ELSE IF( ITYPE.EQ.3 ) THEN
                    435: *
                    436: *           For B*A*x=(lambda)*x;
1.9       bertrand  437: *           backtransform eigenvectors: x = L*y or U**T*y
1.1       bertrand  438: *
                    439:             IF( UPPER ) THEN
                    440:                TRANS = 'T'
                    441:             ELSE
                    442:                TRANS = 'N'
                    443:             END IF
                    444: *
                    445:             CALL DTRMM( 'Left', UPLO, TRANS, 'Non-unit', N, M, ONE, B,
                    446:      $                  LDB, Z, LDZ )
                    447:          END IF
                    448:       END IF
                    449: *
                    450: *     Set WORK(1) to optimal workspace size.
                    451: *
                    452:       WORK( 1 ) = LWKOPT
                    453: *
                    454:       RETURN
                    455: *
                    456: *     End of DSYGVX
                    457: *
                    458:       END

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