LAPACK 3.3.1
Linear Algebra PACKage

ssbgvx.f

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00001       SUBROUTINE SSBGVX( JOBZ, RANGE, UPLO, N, KA, KB, AB, LDAB, BB,
00002      $                   LDBB, Q, LDQ, VL, VU, IL, IU, ABSTOL, M, W, Z,
00003      $                   LDZ, WORK, IWORK, IFAIL, INFO )
00004 *
00005 *  -- LAPACK driver routine (version 3.2) --
00006 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00007 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00008 *     November 2006
00009 *
00010 *     .. Scalar Arguments ..
00011       CHARACTER          JOBZ, RANGE, UPLO
00012       INTEGER            IL, INFO, IU, KA, KB, LDAB, LDBB, LDQ, LDZ, M,
00013      $                   N
00014       REAL               ABSTOL, VL, VU
00015 *     ..
00016 *     .. Array Arguments ..
00017       INTEGER            IFAIL( * ), IWORK( * )
00018       REAL               AB( LDAB, * ), BB( LDBB, * ), Q( LDQ, * ),
00019      $                   W( * ), WORK( * ), Z( LDZ, * )
00020 *     ..
00021 *
00022 *  Purpose
00023 *  =======
00024 *
00025 *  SSBGVX computes selected eigenvalues, and optionally, eigenvectors
00026 *  of a real generalized symmetric-definite banded eigenproblem, of
00027 *  the form A*x=(lambda)*B*x.  Here A and B are assumed to be symmetric
00028 *  and banded, and B is also positive definite.  Eigenvalues and
00029 *  eigenvectors can be selected by specifying either all eigenvalues,
00030 *  a range of values or a range of indices for the desired eigenvalues.
00031 *
00032 *  Arguments
00033 *  =========
00034 *
00035 *  JOBZ    (input) CHARACTER*1
00036 *          = 'N':  Compute eigenvalues only;
00037 *          = 'V':  Compute eigenvalues and eigenvectors.
00038 *
00039 *  RANGE   (input) CHARACTER*1
00040 *          = 'A': all eigenvalues will be found.
00041 *          = 'V': all eigenvalues in the half-open interval (VL,VU]
00042 *                 will be found.
00043 *          = 'I': the IL-th through IU-th eigenvalues will be found.
00044 *
00045 *  UPLO    (input) CHARACTER*1
00046 *          = 'U':  Upper triangles of A and B are stored;
00047 *          = 'L':  Lower triangles of A and B are stored.
00048 *
00049 *  N       (input) INTEGER
00050 *          The order of the matrices A and B.  N >= 0.
00051 *
00052 *  KA      (input) INTEGER
00053 *          The number of superdiagonals of the matrix A if UPLO = 'U',
00054 *          or the number of subdiagonals if UPLO = 'L'.  KA >= 0.
00055 *
00056 *  KB      (input) INTEGER
00057 *          The number of superdiagonals of the matrix B if UPLO = 'U',
00058 *          or the number of subdiagonals if UPLO = 'L'.  KB >= 0.
00059 *
00060 *  AB      (input/output) REAL array, dimension (LDAB, N)
00061 *          On entry, the upper or lower triangle of the symmetric band
00062 *          matrix A, stored in the first ka+1 rows of the array.  The
00063 *          j-th column of A is stored in the j-th column of the array AB
00064 *          as follows:
00065 *          if UPLO = 'U', AB(ka+1+i-j,j) = A(i,j) for max(1,j-ka)<=i<=j;
00066 *          if UPLO = 'L', AB(1+i-j,j)    = A(i,j) for j<=i<=min(n,j+ka).
00067 *
00068 *          On exit, the contents of AB are destroyed.
00069 *
00070 *  LDAB    (input) INTEGER
00071 *          The leading dimension of the array AB.  LDAB >= KA+1.
00072 *
00073 *  BB      (input/output) REAL array, dimension (LDBB, N)
00074 *          On entry, the upper or lower triangle of the symmetric band
00075 *          matrix B, stored in the first kb+1 rows of the array.  The
00076 *          j-th column of B is stored in the j-th column of the array BB
00077 *          as follows:
00078 *          if UPLO = 'U', BB(ka+1+i-j,j) = B(i,j) for max(1,j-kb)<=i<=j;
00079 *          if UPLO = 'L', BB(1+i-j,j)    = B(i,j) for j<=i<=min(n,j+kb).
00080 *
00081 *          On exit, the factor S from the split Cholesky factorization
00082 *          B = S**T*S, as returned by SPBSTF.
00083 *
00084 *  LDBB    (input) INTEGER
00085 *          The leading dimension of the array BB.  LDBB >= KB+1.
00086 *
00087 *  Q       (output) REAL array, dimension (LDQ, N)
00088 *          If JOBZ = 'V', the n-by-n matrix used in the reduction of
00089 *          A*x = (lambda)*B*x to standard form, i.e. C*x = (lambda)*x,
00090 *          and consequently C to tridiagonal form.
00091 *          If JOBZ = 'N', the array Q is not referenced.
00092 *
00093 *  LDQ     (input) INTEGER
00094 *          The leading dimension of the array Q.  If JOBZ = 'N',
00095 *          LDQ >= 1. If JOBZ = 'V', LDQ >= max(1,N).
00096 *
00097 *  VL      (input) REAL
00098 *  VU      (input) REAL
00099 *          If RANGE='V', the lower and upper bounds of the interval to
00100 *          be searched for eigenvalues. VL < VU.
00101 *          Not referenced if RANGE = 'A' or 'I'.
00102 *
00103 *  IL      (input) INTEGER
00104 *  IU      (input) INTEGER
00105 *          If RANGE='I', the indices (in ascending order) of the
00106 *          smallest and largest eigenvalues to be returned.
00107 *          1 <= IL <= IU <= N, if N > 0; IL = 1 and IU = 0 if N = 0.
00108 *          Not referenced if RANGE = 'A' or 'V'.
00109 *
00110 *  ABSTOL  (input) REAL
00111 *          The absolute error tolerance for the eigenvalues.
00112 *          An approximate eigenvalue is accepted as converged
00113 *          when it is determined to lie in an interval [a,b]
00114 *          of width less than or equal to
00115 *
00116 *                  ABSTOL + EPS *   max( |a|,|b| ) ,
00117 *
00118 *          where EPS is the machine precision.  If ABSTOL is less than
00119 *          or equal to zero, then  EPS*|T|  will be used in its place,
00120 *          where |T| is the 1-norm of the tridiagonal matrix obtained
00121 *          by reducing A to tridiagonal form.
00122 *
00123 *          Eigenvalues will be computed most accurately when ABSTOL is
00124 *          set to twice the underflow threshold 2*SLAMCH('S'), not zero.
00125 *          If this routine returns with INFO>0, indicating that some
00126 *          eigenvectors did not converge, try setting ABSTOL to
00127 *          2*SLAMCH('S').
00128 *
00129 *  M       (output) INTEGER
00130 *          The total number of eigenvalues found.  0 <= M <= N.
00131 *          If RANGE = 'A', M = N, and if RANGE = 'I', M = IU-IL+1.
00132 *
00133 *  W       (output) REAL array, dimension (N)
00134 *          If INFO = 0, the eigenvalues in ascending order.
00135 *
00136 *  Z       (output) REAL array, dimension (LDZ, N)
00137 *          If JOBZ = 'V', then if INFO = 0, Z contains the matrix Z of
00138 *          eigenvectors, with the i-th column of Z holding the
00139 *          eigenvector associated with W(i).  The eigenvectors are
00140 *          normalized so Z**T*B*Z = I.
00141 *          If JOBZ = 'N', then Z is not referenced.
00142 *
00143 *  LDZ     (input) INTEGER
00144 *          The leading dimension of the array Z.  LDZ >= 1, and if
00145 *          JOBZ = 'V', LDZ >= max(1,N).
00146 *
00147 *  WORK    (workspace/output) REAL array, dimension (7N)
00148 *
00149 *  IWORK   (workspace/output) INTEGER array, dimension (5N)
00150 *
00151 *  IFAIL   (output) INTEGER array, dimension (M)
00152 *          If JOBZ = 'V', then if INFO = 0, the first M elements of
00153 *          IFAIL are zero.  If INFO > 0, then IFAIL contains the
00154 *          indices of the eigenvalues that failed to converge.
00155 *          If JOBZ = 'N', then IFAIL is not referenced.
00156 *
00157 *  INFO    (output) INTEGER
00158 *          = 0 : successful exit
00159 *          < 0 : if INFO = -i, the i-th argument had an illegal value
00160 *          <= N: if INFO = i, then i eigenvectors failed to converge.
00161 *                  Their indices are stored in IFAIL.
00162 *          > N : SPBSTF returned an error code; i.e.,
00163 *                if INFO = N + i, for 1 <= i <= N, then the leading
00164 *                minor of order i of B is not positive definite.
00165 *                The factorization of B could not be completed and
00166 *                no eigenvalues or eigenvectors were computed.
00167 *
00168 *  Further Details
00169 *  ===============
00170 *
00171 *  Based on contributions by
00172 *     Mark Fahey, Department of Mathematics, Univ. of Kentucky, USA
00173 *
00174 *  =====================================================================
00175 *
00176 *     .. Parameters ..
00177       REAL               ZERO, ONE
00178       PARAMETER          ( ZERO = 0.0E+0, ONE = 1.0E+0 )
00179 *     ..
00180 *     .. Local Scalars ..
00181       LOGICAL            ALLEIG, INDEIG, TEST, UPPER, VALEIG, WANTZ
00182       CHARACTER          ORDER, VECT
00183       INTEGER            I, IINFO, INDD, INDE, INDEE, INDIBL, INDISP,
00184      $                   INDIWO, INDWRK, ITMP1, J, JJ, NSPLIT
00185       REAL               TMP1
00186 *     ..
00187 *     .. External Functions ..
00188       LOGICAL            LSAME
00189       EXTERNAL           LSAME
00190 *     ..
00191 *     .. External Subroutines ..
00192       EXTERNAL           SCOPY, SGEMV, SLACPY, SPBSTF, SSBGST, SSBTRD,
00193      $                   SSTEBZ, SSTEIN, SSTEQR, SSTERF, SSWAP, XERBLA
00194 *     ..
00195 *     .. Intrinsic Functions ..
00196       INTRINSIC          MIN
00197 *     ..
00198 *     .. Executable Statements ..
00199 *
00200 *     Test the input parameters.
00201 *
00202       WANTZ = LSAME( JOBZ, 'V' )
00203       UPPER = LSAME( UPLO, 'U' )
00204       ALLEIG = LSAME( RANGE, 'A' )
00205       VALEIG = LSAME( RANGE, 'V' )
00206       INDEIG = LSAME( RANGE, 'I' )
00207 *
00208       INFO = 0
00209       IF( .NOT.( WANTZ .OR. LSAME( JOBZ, 'N' ) ) ) THEN
00210          INFO = -1
00211       ELSE IF( .NOT.( ALLEIG .OR. VALEIG .OR. INDEIG ) ) THEN
00212          INFO = -2
00213       ELSE IF( .NOT.( UPPER .OR. LSAME( UPLO, 'L' ) ) ) THEN
00214          INFO = -3
00215       ELSE IF( N.LT.0 ) THEN
00216          INFO = -4
00217       ELSE IF( KA.LT.0 ) THEN
00218          INFO = -5
00219       ELSE IF( KB.LT.0 .OR. KB.GT.KA ) THEN
00220          INFO = -6
00221       ELSE IF( LDAB.LT.KA+1 ) THEN
00222          INFO = -8
00223       ELSE IF( LDBB.LT.KB+1 ) THEN
00224          INFO = -10
00225       ELSE IF( LDQ.LT.1 .OR. ( WANTZ .AND. LDQ.LT.N ) ) THEN
00226          INFO = -12
00227       ELSE
00228          IF( VALEIG ) THEN
00229             IF( N.GT.0 .AND. VU.LE.VL )
00230      $         INFO = -14
00231          ELSE IF( INDEIG ) THEN
00232             IF( IL.LT.1 .OR. IL.GT.MAX( 1, N ) ) THEN
00233                INFO = -15
00234             ELSE IF ( IU.LT.MIN( N, IL ) .OR. IU.GT.N ) THEN
00235                INFO = -16
00236             END IF
00237          END IF
00238       END IF
00239       IF( INFO.EQ.0) THEN
00240          IF( LDZ.LT.1 .OR. ( WANTZ .AND. LDZ.LT.N ) ) THEN
00241             INFO = -21
00242          END IF
00243       END IF
00244 *
00245       IF( INFO.NE.0 ) THEN
00246          CALL XERBLA( 'SSBGVX', -INFO )
00247          RETURN
00248       END IF
00249 *
00250 *     Quick return if possible
00251 *
00252       M = 0
00253       IF( N.EQ.0 )
00254      $   RETURN
00255 *
00256 *     Form a split Cholesky factorization of B.
00257 *
00258       CALL SPBSTF( UPLO, N, KB, BB, LDBB, INFO )
00259       IF( INFO.NE.0 ) THEN
00260          INFO = N + INFO
00261          RETURN
00262       END IF
00263 *
00264 *     Transform problem to standard eigenvalue problem.
00265 *
00266       CALL SSBGST( JOBZ, UPLO, N, KA, KB, AB, LDAB, BB, LDBB, Q, LDQ,
00267      $             WORK, IINFO )
00268 *
00269 *     Reduce symmetric band matrix to tridiagonal form.
00270 *
00271       INDD = 1
00272       INDE = INDD + N
00273       INDWRK = INDE + N
00274       IF( WANTZ ) THEN
00275          VECT = 'U'
00276       ELSE
00277          VECT = 'N'
00278       END IF
00279       CALL SSBTRD( VECT, UPLO, N, KA, AB, LDAB, WORK( INDD ),
00280      $             WORK( INDE ), Q, LDQ, WORK( INDWRK ), IINFO )
00281 *
00282 *     If all eigenvalues are desired and ABSTOL is less than or equal
00283 *     to zero, then call SSTERF or SSTEQR.  If this fails for some
00284 *     eigenvalue, then try SSTEBZ.
00285 *
00286       TEST = .FALSE.
00287       IF( INDEIG ) THEN
00288          IF( IL.EQ.1 .AND. IU.EQ.N ) THEN
00289             TEST = .TRUE.
00290          END IF
00291       END IF
00292       IF( ( ALLEIG .OR. TEST ) .AND. ( ABSTOL.LE.ZERO ) ) THEN
00293          CALL SCOPY( N, WORK( INDD ), 1, W, 1 )
00294          INDEE = INDWRK + 2*N
00295          CALL SCOPY( N-1, WORK( INDE ), 1, WORK( INDEE ), 1 )
00296          IF( .NOT.WANTZ ) THEN
00297             CALL SSTERF( N, W, WORK( INDEE ), INFO )
00298          ELSE
00299             CALL SLACPY( 'A', N, N, Q, LDQ, Z, LDZ )
00300             CALL SSTEQR( JOBZ, N, W, WORK( INDEE ), Z, LDZ,
00301      $                   WORK( INDWRK ), INFO )
00302             IF( INFO.EQ.0 ) THEN
00303                DO 10 I = 1, N
00304                   IFAIL( I ) = 0
00305    10          CONTINUE
00306             END IF
00307          END IF
00308          IF( INFO.EQ.0 ) THEN
00309             M = N
00310             GO TO 30
00311          END IF
00312          INFO = 0
00313       END IF
00314 *
00315 *     Otherwise, call SSTEBZ and, if eigenvectors are desired,
00316 *     call SSTEIN.
00317 *
00318       IF( WANTZ ) THEN
00319          ORDER = 'B'
00320       ELSE
00321          ORDER = 'E'
00322       END IF
00323       INDIBL = 1
00324       INDISP = INDIBL + N
00325       INDIWO = INDISP + N
00326       CALL SSTEBZ( RANGE, ORDER, N, VL, VU, IL, IU, ABSTOL,
00327      $             WORK( INDD ), WORK( INDE ), M, NSPLIT, W,
00328      $             IWORK( INDIBL ), IWORK( INDISP ), WORK( INDWRK ),
00329      $             IWORK( INDIWO ), INFO )
00330 *
00331       IF( WANTZ ) THEN
00332          CALL SSTEIN( N, WORK( INDD ), WORK( INDE ), M, W,
00333      $                IWORK( INDIBL ), IWORK( INDISP ), Z, LDZ,
00334      $                WORK( INDWRK ), IWORK( INDIWO ), IFAIL, INFO )
00335 *
00336 *        Apply transformation matrix used in reduction to tridiagonal
00337 *        form to eigenvectors returned by SSTEIN.
00338 *
00339          DO 20 J = 1, M
00340             CALL SCOPY( N, Z( 1, J ), 1, WORK( 1 ), 1 )
00341             CALL SGEMV( 'N', N, N, ONE, Q, LDQ, WORK, 1, ZERO,
00342      $                  Z( 1, J ), 1 )
00343    20    CONTINUE
00344       END IF
00345 *
00346    30 CONTINUE
00347 *
00348 *     If eigenvalues are not in order, then sort them, along with
00349 *     eigenvectors.
00350 *
00351       IF( WANTZ ) THEN
00352          DO 50 J = 1, M - 1
00353             I = 0
00354             TMP1 = W( J )
00355             DO 40 JJ = J + 1, M
00356                IF( W( JJ ).LT.TMP1 ) THEN
00357                   I = JJ
00358                   TMP1 = W( JJ )
00359                END IF
00360    40       CONTINUE
00361 *
00362             IF( I.NE.0 ) THEN
00363                ITMP1 = IWORK( INDIBL+I-1 )
00364                W( I ) = W( J )
00365                IWORK( INDIBL+I-1 ) = IWORK( INDIBL+J-1 )
00366                W( J ) = TMP1
00367                IWORK( INDIBL+J-1 ) = ITMP1
00368                CALL SSWAP( N, Z( 1, I ), 1, Z( 1, J ), 1 )
00369                IF( INFO.NE.0 ) THEN
00370                   ITMP1 = IFAIL( I )
00371                   IFAIL( I ) = IFAIL( J )
00372                   IFAIL( J ) = ITMP1
00373                END IF
00374             END IF
00375    50    CONTINUE
00376       END IF
00377 *
00378       RETURN
00379 *
00380 *     End of SSBGVX
00381 *
00382       END
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