CXML
        	    
LAPACK version 3.0
cgeqrf(3)

PURPOSE
  CGEQRF - compute a QR factorization of a complex M-by-N matrix A

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

      INTEGER	     INFO, LDA, LWORK, M, N

      COMPLEX	     A( LDA, * ), TAU( * ), WORK( * )

DESCRIPTION
  CGEQRF computes a QR factorization of a complex M-by-N matrix A: A = Q * R.

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) COMPLEX array, dimension (LDA,N)
	  On entry, the M-by-N matrix A.  On exit, the elements on and above
	  the diagonal of the array contain the min(M,N)-by-N upper
	  trapezoidal matrix R (R is upper triangular if m >= n); the
	  elements below the diagonal, with the array TAU, represent the
	  unitary 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) COMPLEX array, dimension (min(M,N))
	  The scalar factors of the elementary reflectors (see Further
	  Details).

  WORK	  (workspace/output) COMPLEX 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,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.

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