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## sstev()

subroutine sstev | ( | character | jobz,
|  | integer | n,
|  | real, dimension( * ) | d,
|  | real, dimension( * ) | e,
|  | real, dimension( ldz, * ) | z,
|  | integer | ldz,
|  | real, dimension( * ) | work,
|  | integer | info )

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

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

Purpose:

      !>
      !> SSTEV computes all eigenvalues and, optionally, eigenvectors of a
      !> real symmetric tridiagonal matrix A.
      !>

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 REAL 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 REAL 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 REAL 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 REAL array, dimension (max(1,2*N-2))
      !>          If JOBZ = 'N', WORK is not referenced.
      !>

  [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.