dstedc.f(3)

NAME
dstedc.f -

SYNOPSIS

  Functions/Subroutines
subroutine dstedc (COMPZ, N, D, E, Z, LDZ, WORK, LWORK, IWORK, LIWORK, INFO)
DSTEDC

Function/Subroutine Documentation

  subroutine dstedc (characterCOMPZ, integerN, double precision, dimension( * )D, double precision, dimension( * )E, double precision, dimension( ldz, * )Z, integerLDZ, double precision, dimension( * )WORK, integerLWORK, integer, dimension( * )IWORK, integerLIWORK, integerINFO)

Purpose:

     DSTEDC computes all eigenvalues and, optionally, eigenvectors of a
     symmetric tridiagonal matrix using the divide and conquer method.
     The eigenvectors of a full or band real symmetric matrix can also be
     found if DSYTRD or DSPTRD or DSBTRD 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 dense symmetric
                      matrix also.  On entry, Z contains the orthogonal
                      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 DOUBLE PRECISION array, dimension (LDZ,N)
              On entry, if COMPZ = 'V', then Z contains the orthogonal
              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 symmetric 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 DOUBLE PRECISION array,
                                             dimension (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 N <= 1 then LWORK must be at least 1.
              If COMPZ = 'V' and N > 1 then LWORK 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 then LWORK must be at least
                             ( 1 + 4*N + 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 LWORK need
              only be max(1,2*(N-1)).
              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.

    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 then LIWORK must be at least 1.
              If COMPZ = 'V' and N > 1 then LIWORK must be at least
                             ( 6 + 6*N + 5*N*lg N ).
              If COMPZ = 'I' and N > 1 then 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 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.

    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:
    November 2015

Contributors:
    Jeff Rutter, Computer Science Division, University of California at Berkeley, USA
     Modified by Francoise Tisseur, University of Tennessee

Definition at line 189 of file dstedc.f.

Author

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