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LAPACK version 3.0
dgerqf(3)

PURPOSE
  DGERQF - compute an RQ factorization of a real M-by-N matrix A

SYNTAX
  SUBROUTINE DGERQF( M, N, A, LDA, TAU, WORK, LWORK, INFO )

      INTEGER	     INFO, LDA, LWORK, M, N

      DOUBLE	     PRECISION A( LDA, * ), TAU( * ), WORK( * )

DESCRIPTION
  DGERQF computes an RQ factorization of a real M-by-N matrix A: A = R * Q.

ARGUMENTS
  M	  (input) INTEGER
	  The number of rows of the matrix A.  M >= 0.

  N	  (input) INTEGER
	  The number of columns of the matrix A.  N >= 0.

  A	  (input/output) DOUBLE PRECISION array, dimension (LDA,N)
	  On entry, the M-by-N matrix A.  On exit, if m <= n, the upper
	  triangle of the subarray A(1:m,n-m+1:n) contains the M-by-M upper
	  triangular matrix R; if m >= n, the elements on and above the (m-
	  n)-th subdiagonal contain the M-by-N upper trapezoidal matrix R;
	  the remaining elements, with the array TAU, represent the
	  orthogonal matrix Q as a product of min(m,n) elementary reflectors
	  (see Further Details).  LDA	  (input) INTEGER The leading
	  dimension of the array A.  LDA >= max(1,M).

  TAU	  (output) DOUBLE PRECISION array, dimension (min(M,N))
	  The scalar factors of the elementary reflectors (see Further
	  Details).

  WORK	  (workspace/output) DOUBLE PRECISION array, dimension (LWORK)
	  On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

  LWORK	  (input) INTEGER
	  The dimension of the array WORK.  LWORK >= max(1,M).	For optimum
	  performance LWORK >= M*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.

  INFO	  (output) INTEGER
	  = 0:	successful exit
	  < 0:	if INFO = -i, the i-th argument had an illegal value

FURTHER DETAILS
  The matrix Q is represented as a product of elementary reflectors

     Q = H(1) H(2) . . . H(k), where k = min(m,n).

  Each H(i) has the form

     H(i) = I - tau * v * v'

  where tau is a real scalar, and v is a real vector with
  v(n-k+i+1:n) = 0 and v(n-k+i) = 1; v(1:n-k+i-1) is stored on exit in A(m-
  k+i,1:n-k+i-1), and tau in TAU(i).