LAPACK 3.3.1
Linear Algebra PACKage

cheevd.f

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00001       SUBROUTINE CHEEVD( JOBZ, UPLO, N, A, LDA, W, WORK, LWORK, RWORK,
00002      $                   LRWORK, IWORK, LIWORK, INFO )
00003 *
00004 *  -- LAPACK driver routine (version 3.2) --
00005 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00006 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00007 *     November 2006
00008 *
00009 *     .. Scalar Arguments ..
00010       CHARACTER          JOBZ, UPLO
00011       INTEGER            INFO, LDA, LIWORK, LRWORK, LWORK, N
00012 *     ..
00013 *     .. Array Arguments ..
00014       INTEGER            IWORK( * )
00015       REAL               RWORK( * ), W( * )
00016       COMPLEX            A( LDA, * ), WORK( * )
00017 *     ..
00018 *
00019 *  Purpose
00020 *  =======
00021 *
00022 *  CHEEVD computes all eigenvalues and, optionally, eigenvectors of a
00023 *  complex Hermitian matrix A.  If eigenvectors are desired, it uses a
00024 *  divide and conquer algorithm.
00025 *
00026 *  The divide and conquer algorithm makes very mild assumptions about
00027 *  floating point arithmetic. It will work on machines with a guard
00028 *  digit in add/subtract, or on those binary machines without guard
00029 *  digits which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or
00030 *  Cray-2. It could conceivably fail on hexadecimal or decimal machines
00031 *  without guard digits, but we know of none.
00032 *
00033 *  Arguments
00034 *  =========
00035 *
00036 *  JOBZ    (input) CHARACTER*1
00037 *          = 'N':  Compute eigenvalues only;
00038 *          = 'V':  Compute eigenvalues and eigenvectors.
00039 *
00040 *  UPLO    (input) CHARACTER*1
00041 *          = 'U':  Upper triangle of A is stored;
00042 *          = 'L':  Lower triangle of A is stored.
00043 *
00044 *  N       (input) INTEGER
00045 *          The order of the matrix A.  N >= 0.
00046 *
00047 *  A       (input/output) COMPLEX array, dimension (LDA, N)
00048 *          On entry, the Hermitian matrix A.  If UPLO = 'U', the
00049 *          leading N-by-N upper triangular part of A contains the
00050 *          upper triangular part of the matrix A.  If UPLO = 'L',
00051 *          the leading N-by-N lower triangular part of A contains
00052 *          the lower triangular part of the matrix A.
00053 *          On exit, if JOBZ = 'V', then if INFO = 0, A contains the
00054 *          orthonormal eigenvectors of the matrix A.
00055 *          If JOBZ = 'N', then on exit the lower triangle (if UPLO='L')
00056 *          or the upper triangle (if UPLO='U') of A, including the
00057 *          diagonal, is destroyed.
00058 *
00059 *  LDA     (input) INTEGER
00060 *          The leading dimension of the array A.  LDA >= max(1,N).
00061 *
00062 *  W       (output) REAL array, dimension (N)
00063 *          If INFO = 0, the eigenvalues in ascending order.
00064 *
00065 *  WORK    (workspace/output) COMPLEX array, dimension (MAX(1,LWORK))
00066 *          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
00067 *
00068 *  LWORK   (input) INTEGER
00069 *          The length of the array WORK.
00070 *          If N <= 1,                LWORK must be at least 1.
00071 *          If JOBZ  = 'N' and N > 1, LWORK must be at least N + 1.
00072 *          If JOBZ  = 'V' and N > 1, LWORK must be at least 2*N + N**2.
00073 *
00074 *          If LWORK = -1, then a workspace query is assumed; the routine
00075 *          only calculates the optimal sizes of the WORK, RWORK and
00076 *          IWORK arrays, returns these values as the first entries of
00077 *          the WORK, RWORK and IWORK arrays, and no error message
00078 *          related to LWORK or LRWORK or LIWORK is issued by XERBLA.
00079 *
00080 *  RWORK   (workspace/output) REAL array,
00081 *                                         dimension (LRWORK)
00082 *          On exit, if INFO = 0, RWORK(1) returns the optimal LRWORK.
00083 *
00084 *  LRWORK  (input) INTEGER
00085 *          The dimension of the array RWORK.
00086 *          If N <= 1,                LRWORK must be at least 1.
00087 *          If JOBZ  = 'N' and N > 1, LRWORK must be at least N.
00088 *          If JOBZ  = 'V' and N > 1, LRWORK must be at least
00089 *                         1 + 5*N + 2*N**2.
00090 *
00091 *          If LRWORK = -1, then a workspace query is assumed; the
00092 *          routine only calculates the optimal sizes of the WORK, RWORK
00093 *          and IWORK arrays, returns these values as the first entries
00094 *          of the WORK, RWORK and IWORK arrays, and no error message
00095 *          related to LWORK or LRWORK or LIWORK is issued by XERBLA.
00096 *
00097 *  IWORK   (workspace/output) INTEGER array, dimension (MAX(1,LIWORK))
00098 *          On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.
00099 *
00100 *  LIWORK  (input) INTEGER
00101 *          The dimension of the array IWORK.
00102 *          If N <= 1,                LIWORK must be at least 1.
00103 *          If JOBZ  = 'N' and N > 1, LIWORK must be at least 1.
00104 *          If JOBZ  = 'V' and N > 1, LIWORK must be at least 3 + 5*N.
00105 *
00106 *          If LIWORK = -1, then a workspace query is assumed; the
00107 *          routine only calculates the optimal sizes of the WORK, RWORK
00108 *          and IWORK arrays, returns these values as the first entries
00109 *          of the WORK, RWORK and IWORK arrays, and no error message
00110 *          related to LWORK or LRWORK or LIWORK is issued by XERBLA.
00111 *
00112 *  INFO    (output) INTEGER
00113 *          = 0:  successful exit
00114 *          < 0:  if INFO = -i, the i-th argument had an illegal value
00115 *          > 0:  if INFO = i and JOBZ = 'N', then the algorithm failed
00116 *                to converge; i off-diagonal elements of an intermediate
00117 *                tridiagonal form did not converge to zero;
00118 *                if INFO = i and JOBZ = 'V', then the algorithm failed
00119 *                to compute an eigenvalue while working on the submatrix
00120 *                lying in rows and columns INFO/(N+1) through
00121 *                mod(INFO,N+1).
00122 *
00123 *  Further Details
00124 *  ===============
00125 *
00126 *  Based on contributions by
00127 *     Jeff Rutter, Computer Science Division, University of California
00128 *     at Berkeley, USA
00129 *
00130 *  Modified description of INFO. Sven, 16 Feb 05.
00131 *  =====================================================================
00132 *
00133 *     .. Parameters ..
00134       REAL               ZERO, ONE
00135       PARAMETER          ( ZERO = 0.0E0, ONE = 1.0E0 )
00136       COMPLEX            CONE
00137       PARAMETER          ( CONE = ( 1.0E0, 0.0E0 ) )
00138 *     ..
00139 *     .. Local Scalars ..
00140       LOGICAL            LOWER, LQUERY, WANTZ
00141       INTEGER            IINFO, IMAX, INDE, INDRWK, INDTAU, INDWK2,
00142      $                   INDWRK, ISCALE, LIOPT, LIWMIN, LLRWK, LLWORK,
00143      $                   LLWRK2, LOPT, LROPT, LRWMIN, LWMIN
00144       REAL               ANRM, BIGNUM, EPS, RMAX, RMIN, SAFMIN, SIGMA,
00145      $                   SMLNUM
00146 *     ..
00147 *     .. External Functions ..
00148       LOGICAL            LSAME
00149       INTEGER            ILAENV
00150       REAL               CLANHE, SLAMCH
00151       EXTERNAL           ILAENV, LSAME, CLANHE, SLAMCH
00152 *     ..
00153 *     .. External Subroutines ..
00154       EXTERNAL           CHETRD, CLACPY, CLASCL, CSTEDC, CUNMTR, SSCAL,
00155      $                   SSTERF, XERBLA
00156 *     ..
00157 *     .. Intrinsic Functions ..
00158       INTRINSIC          MAX, SQRT
00159 *     ..
00160 *     .. Executable Statements ..
00161 *
00162 *     Test the input parameters.
00163 *
00164       WANTZ = LSAME( JOBZ, 'V' )
00165       LOWER = LSAME( UPLO, 'L' )
00166       LQUERY = ( LWORK.EQ.-1 .OR. LRWORK.EQ.-1 .OR. LIWORK.EQ.-1 )
00167 *
00168       INFO = 0
00169       IF( .NOT.( WANTZ .OR. LSAME( JOBZ, 'N' ) ) ) THEN
00170          INFO = -1
00171       ELSE IF( .NOT.( LOWER .OR. LSAME( UPLO, 'U' ) ) ) THEN
00172          INFO = -2
00173       ELSE IF( N.LT.0 ) THEN
00174          INFO = -3
00175       ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
00176          INFO = -5
00177       END IF
00178 *
00179       IF( INFO.EQ.0 ) THEN
00180          IF( N.LE.1 ) THEN
00181             LWMIN = 1
00182             LRWMIN = 1
00183             LIWMIN = 1
00184             LOPT = LWMIN
00185             LROPT = LRWMIN
00186             LIOPT = LIWMIN
00187          ELSE
00188             IF( WANTZ ) THEN
00189                LWMIN = 2*N + N*N
00190                LRWMIN = 1 + 5*N + 2*N**2
00191                LIWMIN = 3 + 5*N
00192             ELSE
00193                LWMIN = N + 1
00194                LRWMIN = N
00195                LIWMIN = 1
00196             END IF
00197             LOPT = MAX( LWMIN, N +
00198      $                  ILAENV( 1, 'CHETRD', UPLO, N, -1, -1, -1 ) )
00199             LROPT = LRWMIN
00200             LIOPT = LIWMIN
00201          END IF
00202          WORK( 1 ) = LOPT
00203          RWORK( 1 ) = LROPT
00204          IWORK( 1 ) = LIOPT
00205 *
00206          IF( LWORK.LT.LWMIN .AND. .NOT.LQUERY ) THEN
00207             INFO = -8
00208          ELSE IF( LRWORK.LT.LRWMIN .AND. .NOT.LQUERY ) THEN
00209             INFO = -10
00210          ELSE IF( LIWORK.LT.LIWMIN .AND. .NOT.LQUERY ) THEN
00211             INFO = -12
00212          END IF
00213       END IF
00214 *
00215       IF( INFO.NE.0 ) THEN
00216          CALL XERBLA( 'CHEEVD', -INFO )
00217          RETURN 
00218       ELSE IF( LQUERY ) THEN
00219          RETURN
00220       END IF
00221 *
00222 *     Quick return if possible
00223 *
00224       IF( N.EQ.0 )
00225      $   RETURN
00226 *
00227       IF( N.EQ.1 ) THEN
00228          W( 1 ) = A( 1, 1 )
00229          IF( WANTZ )
00230      $      A( 1, 1 ) = CONE
00231          RETURN
00232       END IF
00233 *
00234 *     Get machine constants.
00235 *
00236       SAFMIN = SLAMCH( 'Safe minimum' )
00237       EPS = SLAMCH( 'Precision' )
00238       SMLNUM = SAFMIN / EPS
00239       BIGNUM = ONE / SMLNUM
00240       RMIN = SQRT( SMLNUM )
00241       RMAX = SQRT( BIGNUM )
00242 *
00243 *     Scale matrix to allowable range, if necessary.
00244 *
00245       ANRM = CLANHE( 'M', UPLO, N, A, LDA, RWORK )
00246       ISCALE = 0
00247       IF( ANRM.GT.ZERO .AND. ANRM.LT.RMIN ) THEN
00248          ISCALE = 1
00249          SIGMA = RMIN / ANRM
00250       ELSE IF( ANRM.GT.RMAX ) THEN
00251          ISCALE = 1
00252          SIGMA = RMAX / ANRM
00253       END IF
00254       IF( ISCALE.EQ.1 )
00255      $   CALL CLASCL( UPLO, 0, 0, ONE, SIGMA, N, N, A, LDA, INFO )
00256 *
00257 *     Call CHETRD to reduce Hermitian matrix to tridiagonal form.
00258 *
00259       INDE = 1
00260       INDTAU = 1
00261       INDWRK = INDTAU + N
00262       INDRWK = INDE + N
00263       INDWK2 = INDWRK + N*N
00264       LLWORK = LWORK - INDWRK + 1
00265       LLWRK2 = LWORK - INDWK2 + 1
00266       LLRWK = LRWORK - INDRWK + 1
00267       CALL CHETRD( UPLO, N, A, LDA, W, RWORK( INDE ), WORK( INDTAU ),
00268      $             WORK( INDWRK ), LLWORK, IINFO )
00269 *
00270 *     For eigenvalues only, call SSTERF.  For eigenvectors, first call
00271 *     CSTEDC to generate the eigenvector matrix, WORK(INDWRK), of the
00272 *     tridiagonal matrix, then call CUNMTR to multiply it to the
00273 *     Householder transformations represented as Householder vectors in
00274 *     A.
00275 *
00276       IF( .NOT.WANTZ ) THEN
00277          CALL SSTERF( N, W, RWORK( INDE ), INFO )
00278       ELSE
00279          CALL CSTEDC( 'I', N, W, RWORK( INDE ), WORK( INDWRK ), N,
00280      $                WORK( INDWK2 ), LLWRK2, RWORK( INDRWK ), LLRWK,
00281      $                IWORK, LIWORK, INFO )
00282          CALL CUNMTR( 'L', UPLO, 'N', N, N, A, LDA, WORK( INDTAU ),
00283      $                WORK( INDWRK ), N, WORK( INDWK2 ), LLWRK2, IINFO )
00284          CALL CLACPY( 'A', N, N, WORK( INDWRK ), N, A, LDA )
00285       END IF
00286 *
00287 *     If matrix was scaled, then rescale eigenvalues appropriately.
00288 *
00289       IF( ISCALE.EQ.1 ) THEN
00290          IF( INFO.EQ.0 ) THEN
00291             IMAX = N
00292          ELSE
00293             IMAX = INFO - 1
00294          END IF
00295          CALL SSCAL( IMAX, ONE / SIGMA, W, 1 )
00296       END IF
00297 *
00298       WORK( 1 ) = LOPT
00299       RWORK( 1 ) = LROPT
00300       IWORK( 1 ) = LIOPT
00301 *
00302       RETURN
00303 *
00304 *     End of CHEEVD
00305 *
00306       END
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