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## sopgtr()

subroutine sopgtr | ( | character | uplo,
|  | integer | n,
|  | real, dimension( * ) | ap,
|  | real, dimension( * ) | tau,
|  | real, dimension( ldq, * ) | q,
|  | integer | ldq,
|  | real, dimension( * ) | work,
|  | integer | info )

SOPGTR

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

Purpose:

      !>
      !> SOPGTR generates a real orthogonal matrix Q which is defined as the
      !> product of n-1 elementary reflectors H(i) of order n, as returned by
      !> SSPTRD using packed storage:
      !>
      !> 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 triangular packed storage used in previous
      !>                 call to SSPTRD;
      !>          = 'L': Lower triangular packed storage used in previous
      !>                 call to SSPTRD.
      !>

  [in]

  N

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

  [in]

  AP

      !>          AP is REAL array, dimension (N*(N+1)/2)
      !>          The vectors which define the elementary reflectors, as
      !>          returned by SSPTRD.
      !>

  [in]

  TAU

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

  [out]

  Q

      !>          Q is REAL array, dimension (LDQ,N)
      !>          The N-by-N orthogonal matrix Q.
      !>

  [in]

  LDQ

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

  [out]

  WORK

      !>          WORK is REAL array, dimension (N-1)
      !>

  [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.