Return to zgeqr2.f CVS log

Up to [local] / rpl / lapack / lapack

Annotation of rpl/lapack/lapack/zgeqr2.f, revision 1.1

1.1     ! bertrand    1:       SUBROUTINE ZGEQR2( M, N, A, LDA, TAU, WORK, INFO )
        !             2: *
        !             3: *  -- LAPACK routine (version 3.2) --
        !             4: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
        !             5: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
        !             6: *     November 2006
        !             7: *
        !             8: *     .. Scalar Arguments ..
        !             9:       INTEGER            INFO, LDA, M, N
        !            10: *     ..
        !            11: *     .. Array Arguments ..
        !            12:       COMPLEX*16         A( LDA, * ), TAU( * ), WORK( * )
        !            13: *     ..
        !            14: *
        !            15: *  Purpose
        !            16: *  =======
        !            17: *
        !            18: *  ZGEQR2 computes a QR factorization of a complex m by n matrix A:
        !            19: *  A = Q * R.
        !            20: *
        !            21: *  Arguments
        !            22: *  =========
        !            23: *
        !            24: *  M       (input) INTEGER
        !            25: *          The number of rows of the matrix A.  M >= 0.
        !            26: *
        !            27: *  N       (input) INTEGER
        !            28: *          The number of columns of the matrix A.  N >= 0.
        !            29: *
        !            30: *  A       (input/output) COMPLEX*16 array, dimension (LDA,N)
        !            31: *          On entry, the m by n matrix A.
        !            32: *          On exit, the elements on and above the diagonal of the array
        !            33: *          contain the min(m,n) by n upper trapezoidal matrix R (R is
        !            34: *          upper triangular if m >= n); the elements below the diagonal,
        !            35: *          with the array TAU, represent the unitary matrix Q as a
        !            36: *          product of elementary reflectors (see Further Details).
        !            37: *
        !            38: *  LDA     (input) INTEGER
        !            39: *          The leading dimension of the array A.  LDA >= max(1,M).
        !            40: *
        !            41: *  TAU     (output) COMPLEX*16 array, dimension (min(M,N))
        !            42: *          The scalar factors of the elementary reflectors (see Further
        !            43: *          Details).
        !            44: *
        !            45: *  WORK    (workspace) COMPLEX*16 array, dimension (N)
        !            46: *
        !            47: *  INFO    (output) INTEGER
        !            48: *          = 0: successful exit
        !            49: *          < 0: if INFO = -i, the i-th argument had an illegal value
        !            50: *
        !            51: *  Further Details
        !            52: *  ===============
        !            53: *
        !            54: *  The matrix Q is represented as a product of elementary reflectors
        !            55: *
        !            56: *     Q = H(1) H(2) . . . H(k), where k = min(m,n).
        !            57: *
        !            58: *  Each H(i) has the form
        !            59: *
        !            60: *     H(i) = I - tau * v * v'
        !            61: *
        !            62: *  where tau is a complex scalar, and v is a complex vector with
        !            63: *  v(1:i-1) = 0 and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i),
        !            64: *  and tau in TAU(i).
        !            65: *
        !            66: *  =====================================================================
        !            67: *
        !            68: *     .. Parameters ..
        !            69:       COMPLEX*16         ONE
        !            70:       PARAMETER          ( ONE = ( 1.0D+0, 0.0D+0 ) )
        !            71: *     ..
        !            72: *     .. Local Scalars ..
        !            73:       INTEGER            I, K
        !            74:       COMPLEX*16         ALPHA
        !            75: *     ..
        !            76: *     .. External Subroutines ..
        !            77:       EXTERNAL           XERBLA, ZLARF, ZLARFP
        !            78: *     ..
        !            79: *     .. Intrinsic Functions ..
        !            80:       INTRINSIC          DCONJG, MAX, MIN
        !            81: *     ..
        !            82: *     .. Executable Statements ..
        !            83: *
        !            84: *     Test the input arguments
        !            85: *
        !            86:       INFO = 0
        !            87:       IF( M.LT.0 ) THEN
        !            88:          INFO = -1
        !            89:       ELSE IF( N.LT.0 ) THEN
        !            90:          INFO = -2
        !            91:       ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
        !            92:          INFO = -4
        !            93:       END IF
        !            94:       IF( INFO.NE.0 ) THEN
        !            95:          CALL XERBLA( 'ZGEQR2', -INFO )
        !            96:          RETURN
        !            97:       END IF
        !            98: *
        !            99:       K = MIN( M, N )
        !           100: *
        !           101:       DO 10 I = 1, K
        !           102: *
        !           103: *        Generate elementary reflector H(i) to annihilate A(i+1:m,i)
        !           104: *
        !           105:          CALL ZLARFP( M-I+1, A( I, I ), A( MIN( I+1, M ), I ), 1,
        !           106:      $                TAU( I ) )
        !           107:          IF( I.LT.N ) THEN
        !           108: *
        !           109: *           Apply H(i)' to A(i:m,i+1:n) from the left
        !           110: *
        !           111:             ALPHA = A( I, I )
        !           112:             A( I, I ) = ONE
        !           113:             CALL ZLARF( 'Left', M-I+1, N-I, A( I, I ), 1,
        !           114:      $                  DCONJG( TAU( I ) ), A( I, I+1 ), LDA, WORK )
        !           115:             A( I, I ) = ALPHA
        !           116:          END IF
        !           117:    10 CONTINUE
        !           118:       RETURN
        !           119: *
        !           120: *     End of ZGEQR2
        !           121: *
        !           122:       END