LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ cstegr()

subroutine cstegr ( character  jobz,
character  range,
integer  n,
real, dimension( * )  d,
real, dimension( * )  e,
real  vl,
real  vu,
integer  il,
integer  iu,
real  abstol,
integer  m,
real, dimension( * )  w,
complex, dimension( ldz, * )  z,
integer  ldz,
integer, dimension( * )  isuppz,
real, dimension( * )  work,
integer  lwork,
integer, dimension( * )  iwork,
integer  liwork,
integer  info 
)

CSTEGR

Download CSTEGR + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 CSTEGR computes selected eigenvalues and, optionally, eigenvectors
 of a real symmetric tridiagonal matrix T. Any such unreduced matrix has
 a well defined set of pairwise different real eigenvalues, the corresponding
 real eigenvectors are pairwise orthogonal.

 The spectrum may be computed either completely or partially by specifying
 either an interval (VL,VU] or a range of indices IL:IU for the desired
 eigenvalues.

 CSTEGR is a compatibility wrapper around the improved CSTEMR routine.
 See SSTEMR for further details.

 One important change is that the ABSTOL parameter no longer provides any
 benefit and hence is no longer used.

 Note : CSTEGR and CSTEMR work only on machines which follow
 IEEE-754 floating-point standard in their handling of infinities and
 NaNs.  Normal execution may create these exceptional values and hence
 may abort due to a floating point exception in environments which
 do not conform to the IEEE-754 standard.
Parameters
[in]JOBZ
          JOBZ is CHARACTER*1
          = 'N':  Compute eigenvalues only;
          = 'V':  Compute eigenvalues and eigenvectors.
[in]RANGE
          RANGE is CHARACTER*1
          = 'A': all eigenvalues will be found.
          = 'V': all eigenvalues in the half-open interval (VL,VU]
                 will be found.
          = 'I': the IL-th through IU-th eigenvalues will be found.
[in]N
          N is INTEGER
          The order of the matrix.  N >= 0.
[in,out]D
          D is REAL array, dimension (N)
          On entry, the N diagonal elements of the tridiagonal matrix
          T. On exit, D is overwritten.
[in,out]E
          E is REAL array, dimension (N)
          On entry, the (N-1) subdiagonal elements of the tridiagonal
          matrix T in elements 1 to N-1 of E. E(N) need not be set on
          input, but is used internally as workspace.
          On exit, E is overwritten.
[in]VL
          VL is REAL

          If RANGE='V', the lower bound of the interval to
          be searched for eigenvalues. VL < VU.
          Not referenced if RANGE = 'A' or 'I'.
[in]VU
          VU is REAL

          If RANGE='V', the upper bound of the interval to
          be searched for eigenvalues. VL < VU.
          Not referenced if RANGE = 'A' or 'I'.
[in]IL
          IL is INTEGER

          If RANGE='I', the index of the
          smallest eigenvalue to be returned.
          1 <= IL <= IU <= N, if N > 0.
          Not referenced if RANGE = 'A' or 'V'.
[in]IU
          IU is INTEGER

          If RANGE='I', the index of the
          largest eigenvalue to be returned.
          1 <= IL <= IU <= N, if N > 0.
          Not referenced if RANGE = 'A' or 'V'.
[in]ABSTOL
          ABSTOL is REAL
          Unused.  Was the absolute error tolerance for the
          eigenvalues/eigenvectors in previous versions.
[out]M
          M is INTEGER
          The total number of eigenvalues found.  0 <= M <= N.
          If RANGE = 'A', M = N, and if RANGE = 'I', M = IU-IL+1.
[out]W
          W is REAL array, dimension (N)
          The first M elements contain the selected eigenvalues in
          ascending order.
[out]Z
          Z is COMPLEX array, dimension (LDZ, max(1,M) )
          If JOBZ = 'V', and if INFO = 0, then the first M columns of Z
          contain the orthonormal eigenvectors of the matrix T
          corresponding to the selected eigenvalues, with the i-th
          column of Z holding the eigenvector associated with W(i).
          If JOBZ = 'N', then Z is not referenced.
          Note: the user must ensure that at least max(1,M) columns are
          supplied in the array Z; if RANGE = 'V', the exact value of M
          is not known in advance and an upper bound must be used.
          Supplying N columns is always safe.
[in]LDZ
          LDZ is INTEGER
          The leading dimension of the array Z.  LDZ >= 1, and if
          JOBZ = 'V', then LDZ >= max(1,N).
[out]ISUPPZ
          ISUPPZ is INTEGER array, dimension ( 2*max(1,M) )
          The support of the eigenvectors in Z, i.e., the indices
          indicating the nonzero elements in Z. The i-th computed eigenvector
          is nonzero only in elements ISUPPZ( 2*i-1 ) through
          ISUPPZ( 2*i ). This is relevant in the case when the matrix
          is split. ISUPPZ is only accessed when JOBZ is 'V' and N > 0.
[out]WORK
          WORK is REAL array, dimension (LWORK)
          On exit, if INFO = 0, WORK(1) returns the optimal
          (and minimal) LWORK.
[in]LWORK
          LWORK is INTEGER
          The dimension of the array WORK. LWORK >= max(1,18*N)
          if JOBZ = 'V', and LWORK >= max(1,12*N) if JOBZ = 'N'.
          If LWORK = -1, then a workspace query is assumed; the routine
          only calculates the optimal size of the WORK array, returns
          this value as the first entry of the WORK array, and no error
          message related to LWORK is issued by XERBLA.
[out]IWORK
          IWORK is INTEGER array, dimension (LIWORK)
          On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.
[in]LIWORK
          LIWORK is INTEGER
          The dimension of the array IWORK.  LIWORK >= max(1,10*N)
          if the eigenvectors are desired, and LIWORK >= max(1,8*N)
          if only the eigenvalues are to be computed.
          If LIWORK = -1, then a workspace query is assumed; the
          routine only calculates the optimal size of the IWORK array,
          returns this value as the first entry of the IWORK array, and
          no error message related to LIWORK is issued by XERBLA.
[out]INFO
          INFO is INTEGER
          On exit, INFO
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value
          > 0:  if INFO = 1X, internal error in SLARRE,
                if INFO = 2X, internal error in CLARRV.
                Here, the digit X = ABS( IINFO ) < 10, where IINFO is
                the nonzero error code returned by SLARRE or
                CLARRV, respectively.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Contributors:
Inderjit Dhillon, IBM Almaden, USA
Osni Marques, LBNL/NERSC, USA
Christof Voemel, LBNL/NERSC, USA

Definition at line 262 of file cstegr.f.

265*
266* -- LAPACK computational routine --
267* -- LAPACK is a software package provided by Univ. of Tennessee, --
268* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
269*
270* .. Scalar Arguments ..
271 CHARACTER JOBZ, RANGE
272 INTEGER IL, INFO, IU, LDZ, LIWORK, LWORK, M, N
273 REAL ABSTOL, VL, VU
274* ..
275* .. Array Arguments ..
276 INTEGER ISUPPZ( * ), IWORK( * )
277 REAL D( * ), E( * ), W( * ), WORK( * )
278 COMPLEX Z( LDZ, * )
279* ..
280*
281* =====================================================================
282*
283* .. Local Scalars ..
284 LOGICAL TRYRAC
285* ..
286* .. External Subroutines ..
287 EXTERNAL cstemr
288* ..
289* .. Executable Statements ..
290 info = 0
291 tryrac = .false.
292
293 CALL cstemr( jobz, range, n, d, e, vl, vu, il, iu,
294 $ m, w, z, ldz, n, isuppz, tryrac, work, lwork,
295 $ iwork, liwork, info )
296*
297* End of CSTEGR
298*
subroutine cstemr(jobz, range, n, d, e, vl, vu, il, iu, m, w, z, ldz, nzc, isuppz, tryrac, work, lwork, iwork, liwork, info)
CSTEMR
Definition cstemr.f:339
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