Loading...
Searching...
No Matches

## dorgtr()

subroutine dorgtr | ( | character | uplo,
|  | integer | n,
|  | double precision, dimension( lda, * ) | a,
|  | integer | lda,
|  | double precision, dimension( * ) | tau,
|  | double precision, dimension( * ) | work,
|  | integer | lwork,
|  | integer | info )

DORGTR

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

Purpose:

      !>
      !> DORGTR generates a real orthogonal matrix Q which is defined as the
      !> product of n-1 elementary reflectors of order N, as returned by
      !> DSYTRD:
      !>
      !> if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),
      !>
      !> if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).
      !>

Parameters

  [in]

  UPLO

      !>          UPLO is CHARACTER*1
      !>          = 'U': Upper triangle of A contains elementary reflectors
      !>                 from DSYTRD;
      !>          = 'L': Lower triangle of A contains elementary reflectors
      !>                 from DSYTRD.
      !>

  [in]

  N

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

  [in,out]

  A

      !>          A is DOUBLE PRECISION array, dimension (LDA,N)
      !>          On entry, the vectors which define the elementary reflectors,
      !>          as returned by DSYTRD.
      !>          On exit, the N-by-N orthogonal matrix Q.
      !>

  [in]

  LDA

      !>          LDA is INTEGER
      !>          The leading dimension of the array A. LDA >= max(1,N).
      !>

  [in]

  TAU

      !>          TAU is DOUBLE PRECISION array, dimension (N-1)
      !>          TAU(i) must contain the scalar factor of the elementary
      !>          reflector H(i), as returned by DSYTRD.
      !>

  [out]

  WORK

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

  [in]

  LWORK

      !>          LWORK is INTEGER
      !>          The dimension of the array WORK. LWORK >= max(1,N-1).
      !>          For optimum performance LWORK >= (N-1)*NB, where NB is
      !>          the optimal blocksize.
      !>
      !>          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.
      !>

  [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.