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## zungql()

subroutine zungql | ( | integer | m,
|  | integer | n,
|  | integer | k,
|  | complex*16, dimension( lda, * ) | a,
|  | integer | lda,
|  | complex*16, dimension( * ) | tau,
|  | complex*16, dimension( * ) | work,
|  | integer | lwork,
|  | integer | info )

ZUNGQL

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

Purpose:

      !>
      !> ZUNGQL generates an M-by-N complex matrix Q with orthonormal columns,
      !> which is defined as the last N columns of a product of K elementary
      !> reflectors of order M
      !>
      !>       Q  =  H(k) . . . H(2) H(1)
      !>
      !> as returned by ZGEQLF.
      !>

Parameters

  [in]

  M

      !>          M is INTEGER
      !>          The number of rows of the matrix Q. M >= 0.
      !>

  [in]

  N

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

  [in]

  K

      !>          K is INTEGER
      !>          The number of elementary reflectors whose product defines the
      !>          matrix Q. N >= K >= 0.
      !>

  [in,out]

  A

      !>          A is COMPLEX*16 array, dimension (LDA,N)
      !>          On entry, the (n-k+i)-th column must contain the vector which
      !>          defines the elementary reflector H(i), for i = 1,2,...,k, as
      !>          returned by ZGEQLF in the last k columns of its array
      !>          argument A.
      !>          On exit, the M-by-N matrix Q.
      !>

  [in]

  LDA

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

  [in]

  TAU

      !>          TAU is COMPLEX*16 array, dimension (K)
      !>          TAU(i) must contain the scalar factor of the elementary
      !>          reflector H(i), as returned by ZGEQLF.
      !>

  [out]

  WORK

      !>          WORK is COMPLEX*16 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).
      !>          For optimum performance LWORK >= N*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 has an illegal value
      !>

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