Loading...
Searching...
No Matches

## zsteqr()

subroutine zsteqr | ( | character | compz,
|  | integer | n,
|  | double precision, dimension( * ) | d,
|  | double precision, dimension( * ) | e,
|  | complex*16, dimension( ldz, * ) | z,
|  | integer | ldz,
|  | double precision, dimension( * ) | work,
|  | integer | info )

ZSTEQR

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

Purpose:

      !>
      !> ZSTEQR computes all eigenvalues and, optionally, eigenvectors of a
      !> symmetric tridiagonal matrix using the implicit QL or QR 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.
      !>

Parameters

  [in]

  COMPZ

      !>          COMPZ is CHARACTER*1
      !>          = 'N':  Compute eigenvalues only.
      !>          = 'V':  Compute eigenvalues and eigenvectors of the original
      !>                  Hermitian matrix.  On entry, Z must contain the
      !>                  unitary matrix used to reduce the original matrix
      !>                  to tridiagonal form.
      !>          = 'I':  Compute eigenvalues and eigenvectors of the
      !>                  tridiagonal matrix.  Z is initialized to the identity
      !>                  matrix.
      !>

  [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 diagonal elements of the tridiagonal matrix.
      !>          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.
      !>          On exit, E has been destroyed.
      !>

  [in,out]

  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.
      !>

  [in]

  LDZ

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

  [out]

  WORK

      !>          WORK is DOUBLE PRECISION array, dimension (max(1,2*N-2))
      !>          If COMPZ = 'N', then 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:  the algorithm has failed to find all the eigenvalues in
      !>                a total of 30*N iterations; if INFO = i, then i
      !>                elements of E have not converged to zero; on exit, D
      !>                and E contain the elements of a symmetric tridiagonal
      !>                matrix which is unitarily similar to the original
      !>                matrix.
      !>

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