```      SUBROUTINE CGEQR2( M, N, A, LDA, TAU, WORK, INFO )
*
*  -- LAPACK routine (version 3.1) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     .. Scalar Arguments ..
INTEGER            INFO, LDA, M, N
*     ..
*     .. Array Arguments ..
COMPLEX            A( LDA, * ), TAU( * ), WORK( * )
*     ..
*
*  Purpose
*  =======
*
*  CGEQR2 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 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) COMPLEX array, dimension (N)
*
*  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).
*
*  =====================================================================
*
*     .. Parameters ..
COMPLEX            ONE
PARAMETER          ( ONE = ( 1.0E+0, 0.0E+0 ) )
*     ..
*     .. Local Scalars ..
INTEGER            I, K
COMPLEX            ALPHA
*     ..
*     .. External Subroutines ..
EXTERNAL           CLARF, CLARFG, XERBLA
*     ..
*     .. Intrinsic Functions ..
INTRINSIC          CONJG, MAX, MIN
*     ..
*     .. Executable Statements ..
*
*     Test the input arguments
*
INFO = 0
IF( M.LT.0 ) THEN
INFO = -1
ELSE IF( N.LT.0 ) THEN
INFO = -2
ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
INFO = -4
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'CGEQR2', -INFO )
RETURN
END IF
*
K = MIN( M, N )
*
DO 10 I = 1, K
*
*        Generate elementary reflector H(i) to annihilate A(i+1:m,i)
*
CALL CLARFG( M-I+1, A( I, I ), A( MIN( I+1, M ), I ), 1,
\$                TAU( I ) )
IF( I.LT.N ) THEN
*
*           Apply H(i)' to A(i:m,i+1:n) from the left
*
ALPHA = A( I, I )
A( I, I ) = ONE
CALL CLARF( 'Left', M-I+1, N-I, A( I, I ), 1,
\$                  CONJG( TAU( I ) ), A( I, I+1 ), LDA, WORK )
A( I, I ) = ALPHA
END IF
10 CONTINUE
RETURN
*
*     End of CGEQR2
*
END

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