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## dggbak()

subroutine dggbak | ( | character | job,
|  | character | side,
|  | integer | n,
|  | integer | ilo,
|  | integer | ihi,
|  | double precision, dimension( * ) | lscale,
|  | double precision, dimension( * ) | rscale,
|  | integer | m,
|  | double precision, dimension( ldv, * ) | v,
|  | integer | ldv,
|  | integer | info )

DGGBAK

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

Purpose:

      !>
      !> DGGBAK forms the right or left eigenvectors of a real generalized
      !> eigenvalue problem A*x = lambda*B*x, by backward transformation on
      !> the computed eigenvectors of the balanced pair of matrices output by
      !> DGGBAL.
      !>

Parameters

  [in]

  JOB

      !>          JOB is CHARACTER*1
      !>          Specifies the type of backward transformation required:
      !>          = 'N':  do nothing, return immediately;
      !>          = 'P':  do backward transformation for permutation only;
      !>          = 'S':  do backward transformation for scaling only;
      !>          = 'B':  do backward transformations for both permutation and
      !>                  scaling.
      !>          JOB must be the same as the argument JOB supplied to DGGBAL.
      !>

  [in]

  SIDE

      !>          SIDE is CHARACTER*1
      !>          = 'R':  V contains right eigenvectors;
      !>          = 'L':  V contains left eigenvectors.
      !>

  [in]

  N

      !>          N is INTEGER
      !>          The number of rows of the matrix V.  N >= 0.
      !>

  [in]

  ILO

      !>          ILO is INTEGER
      !>

  [in]

  IHI

      !>          IHI is INTEGER
      !>          The integers ILO and IHI determined by DGGBAL.
      !>          1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.
      !>

  [in]

  LSCALE

      !>          LSCALE is DOUBLE PRECISION array, dimension (N)
      !>          Details of the permutations and/or scaling factors applied
      !>          to the left side of A and B, as returned by DGGBAL.
      !>

  [in]

  RSCALE

      !>          RSCALE is DOUBLE PRECISION array, dimension (N)
      !>          Details of the permutations and/or scaling factors applied
      !>          to the right side of A and B, as returned by DGGBAL.
      !>

  [in]

  M

      !>          M is INTEGER
      !>          The number of columns of the matrix V.  M >= 0.
      !>

  [in,out]

  V

      !>          V is DOUBLE PRECISION array, dimension (LDV,M)
      !>          On entry, the matrix of right or left eigenvectors to be
      !>          transformed, as returned by DTGEVC.
      !>          On exit, V is overwritten by the transformed eigenvectors.
      !>

  [in]

  LDV

      !>          LDV is INTEGER
      !>          The leading dimension of the matrix V. LDV >= max(1,N).
      !>

  [out]

  INFO

      !>          INFO is INTEGER
      !>          = 0:  successful exit.
      !>          < 0:  if INFO = -i, the i-th argument had an illegal value.
      !>

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

Further Details:

      !>
      !>  See R.C. Ward, Balancing the generalized eigenvalue problem,
      !>                 SIAM J. Sci. Stat. Comp. 2 (1981), 141-152.
      !>