zstedc.f(3)

NAME
zstedc.f

SYNOPSIS

  Functions/Subroutines
subroutine zstedc (COMPZ, N, D, E, Z, LDZ, WORK, LWORK, RWORK, LRWORK, IWORK, LIWORK, INFO)
ZSTEDC

Function/Subroutine Documentation

  subroutine zstedc (character COMPZ, integer N, double precision, dimension( * ) D, double precision, dimension( * ) E, complex*16, dimension( ldz, * ) Z, integer LDZ, complex*16, dimension( * ) WORK, integer LWORK, double precision, dimension( * ) RWORK, integer LRWORK, integer, dimension( * ) IWORK, integer LIWORK, integer INFO)

ZSTEDC

Purpose:

     ZSTEDC computes all eigenvalues and, optionally, eigenvectors of a
     symmetric tridiagonal matrix using the divide and conquer method.
     The eigenvectors of a full or band complex Hermitian matrix can also
     be found if ZHETRD or ZHPTRD or ZHBTRD has been used to reduce this
     matrix to tridiagonal form.
     This code makes very mild assumptions about floating point
     arithmetic. It will work on machines with a guard digit in
     add/subtract, or on those binary machines without guard digits
     which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or Cray-2.
     It could conceivably fail on hexadecimal or decimal machines
     without guard digits, but we know of none.  See DLAED3 for details.

Parameters:
    COMPZ

              COMPZ is CHARACTER*1
              = 'N':  Compute eigenvalues only.
              = 'I':  Compute eigenvectors of tridiagonal matrix also.
              = 'V':  Compute eigenvectors of original Hermitian matrix
                      also.  On entry, Z contains the unitary matrix used
                      to reduce the original matrix to tridiagonal form.

    N

              N is INTEGER
              The dimension of the symmetric tridiagonal matrix.  N >= 0.

    D

              D is DOUBLE PRECISION array, dimension (N)
              On entry, the diagonal elements of the tridiagonal matrix.
              On exit, if INFO = 0, the eigenvalues in ascending order.

    E

              E is DOUBLE PRECISION array, dimension (N-1)
              On entry, the subdiagonal elements of the tridiagonal matrix.
              On exit, E has been destroyed.

    Z

              Z is COMPLEX*16 array, dimension (LDZ,N)
              On entry, if COMPZ = 'V', then Z contains the unitary
              matrix used in the reduction to tridiagonal form.
              On exit, if INFO = 0, then if COMPZ = 'V', Z contains the
              orthonormal eigenvectors of the original Hermitian matrix,
              and if COMPZ = 'I', Z contains the orthonormal eigenvectors
              of the symmetric tridiagonal matrix.
              If  COMPZ = 'N', then Z is not referenced.

    LDZ

              LDZ is INTEGER
              The leading dimension of the array Z.  LDZ >= 1.
              If eigenvectors are desired, then LDZ >= max(1,N).

    WORK

              WORK is COMPLEX*16 array, dimension (MAX(1,LWORK))
              On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

    LWORK

              LWORK is INTEGER
              The dimension of the array WORK.
              If COMPZ = 'N' or 'I', or N <= 1, LWORK must be at least 1.
              If COMPZ = 'V' and N > 1, LWORK must be at least N*N.
              Note that for COMPZ = 'V', then if N is less than or
              equal to the minimum divide size, usually 25, then LWORK need
              only be 1.
              If LWORK = -1, then a workspace query is assumed; the routine
              only calculates the optimal sizes of the WORK, RWORK and
              IWORK arrays, returns these values as the first entries of
              the WORK, RWORK and IWORK arrays, and no error message
              related to LWORK or LRWORK or LIWORK is issued by XERBLA.

    RWORK

              RWORK is DOUBLE PRECISION array, dimension (MAX(1,LRWORK))
              On exit, if INFO = 0, RWORK(1) returns the optimal LRWORK.

    LRWORK

              LRWORK is INTEGER
              The dimension of the array RWORK.
              If COMPZ = 'N' or N <= 1, LRWORK must be at least 1.
              If COMPZ = 'V' and N > 1, LRWORK must be at least
                             1 + 3*N + 2*N*lg N + 4*N**2 ,
                             where lg( N ) = smallest integer k such
                             that 2**k >= N.
              If COMPZ = 'I' and N > 1, LRWORK must be at least
                             1 + 4*N + 2*N**2 .
              Note that for COMPZ = 'I' or 'V', then if N is less than or
              equal to the minimum divide size, usually 25, then LRWORK
              need only be max(1,2*(N-1)).
              If LRWORK = -1, then a workspace query is assumed; the
              routine only calculates the optimal sizes of the WORK, RWORK
              and IWORK arrays, returns these values as the first entries
              of the WORK, RWORK and IWORK arrays, and no error message
              related to LWORK or LRWORK or LIWORK is issued by XERBLA.

    IWORK

              IWORK is INTEGER array, dimension (MAX(1,LIWORK))
              On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.

    LIWORK

              LIWORK is INTEGER
              The dimension of the array IWORK.
              If COMPZ = 'N' or N <= 1, LIWORK must be at least 1.
              If COMPZ = 'V' or N > 1,  LIWORK must be at least
                                        6 + 6*N + 5*N*lg N.
              If COMPZ = 'I' or N > 1,  LIWORK must be at least
                                        3 + 5*N .
              Note that for COMPZ = 'I' or 'V', then if N is less than or
              equal to the minimum divide size, usually 25, then LIWORK
              need only be 1.
              If LIWORK = -1, then a workspace query is assumed; the
              routine only calculates the optimal sizes of the WORK, RWORK
              and IWORK arrays, returns these values as the first entries
              of the WORK, RWORK and IWORK arrays, and no error message
              related to LWORK or LRWORK or LIWORK is issued by XERBLA.

    INFO

              INFO is INTEGER
              = 0:  successful exit.
              < 0:  if INFO = -i, the i-th argument had an illegal value.
              > 0:  The algorithm failed to compute an eigenvalue while
                    working on the submatrix lying in rows and columns
                    INFO/(N+1) through mod(INFO,N+1).

Author:
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Date:
    June 2017

Contributors:
    Jeff Rutter, Computer Science Division, University of California at Berkeley, USA

Definition at line 214 of file zstedc.f.

Author

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