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## dstevd()

subroutine dstevd | ( | character | jobz,
|  | integer | n,
|  | double precision, dimension( * ) | d,
|  | double precision, dimension( * ) | e,
|  | double precision, dimension( ldz, * ) | z,
|  | integer | ldz,
|  | double precision, dimension( * ) | work,
|  | integer | lwork,
|  | integer, dimension( * ) | iwork,
|  | integer | liwork,
|  | integer | info )

DSTEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices

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

Purpose:

      !>
      !> DSTEVD computes all eigenvalues and, optionally, eigenvectors of a
      !> real symmetric tridiagonal matrix. If eigenvectors are desired, it
      !> uses a divide and conquer algorithm.
      !>
      !>

Parameters

  [in]

  JOBZ

      !>          JOBZ is CHARACTER*1
      !>          = 'N':  Compute eigenvalues only;
      !>          = 'V':  Compute eigenvalues and eigenvectors.
      !>

  [in]

  N

      !>          N is INTEGER
      !>          The order of the matrix.  N >= 0.
      !>

  [in,out]

  D

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

  [in,out]

  E

      !>          E is DOUBLE PRECISION array, dimension (N-1)
      !>          On entry, the (n-1) subdiagonal elements of the tridiagonal
      !>          matrix A, stored in elements 1 to N-1 of E.
      !>          On exit, the contents of E are destroyed.
      !>

  [out]

  Z

      !>          Z is DOUBLE PRECISION array, dimension (LDZ, N)
      !>          If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal
      !>          eigenvectors of the matrix A, with the i-th column of Z
      !>          holding the eigenvector associated with D(i).
      !>          If JOBZ = 'N', then Z is not referenced.
      !>

  [in]

  LDZ

      !>          LDZ is INTEGER
      !>          The leading dimension of the array Z.  LDZ >= 1, and if
      !>          JOBZ = 'V', LDZ >= max(1,N).
      !>

  [out]

  WORK

      !>          WORK is DOUBLE PRECISION array,
      !>                                         dimension (LWORK)
      !>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
      !>

  [in]

  LWORK

      !>          LWORK is INTEGER
      !>          The dimension of the array WORK.
      !>          If JOBZ  = 'N' or N <= 1 then LWORK must be at least 1.
      !>          If JOBZ  = 'V' and N > 1 then LWORK must be at least
      !>                         ( 1 + 4*N + N**2 ).
      !>
      !>          If LWORK = -1, then a workspace query is assumed; the routine
      !>          only calculates the optimal sizes of the WORK and IWORK
      !>          arrays, returns these values as the first entries of the WORK
      !>          and IWORK arrays, and no error message related to LWORK or
      !>          LIWORK is issued by XERBLA.
      !>

  [out]

  IWORK

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

  [in]

  LIWORK

      !>          LIWORK is INTEGER
      !>          The dimension of the array IWORK.
      !>          If JOBZ  = 'N' or N <= 1 then LIWORK must be at least 1.
      !>          If JOBZ  = 'V' and N > 1 then LIWORK must be at least 3+5*N.
      !>
      !>          If LIWORK = -1, then a workspace query is assumed; the
      !>          routine only calculates the optimal sizes of the WORK and
      !>          IWORK arrays, returns these values as the first entries of
      !>          the WORK and IWORK arrays, and no error message related to
      !>          LWORK or LIWORK is issued by XERBLA.
      !>

  [out]

  INFO

      !>          INFO is INTEGER
      !>          = 0:  successful exit
      !>          < 0:  if INFO = -i, the i-th argument had an illegal value
      !>          > 0:  if INFO = i, the algorithm failed to converge; i
      !>                off-diagonal elements of E did not converge to zero.
      !>

Author
  Univ. of Tennessee
  Univ. of California Berkeley
  Univ. of Colorado Denver
  NAG Ltd.