1 *> \brief \b ZUNGL2 generates all or part of the unitary matrix Q from an LQ factorization determined by cgelqf (unblocked algorithm).
3 * =========== DOCUMENTATION ===========
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
9 *> Download ZUNGL2 + dependencies
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14 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zungl2.f">
21 * SUBROUTINE ZUNGL2( M, N, K, A, LDA, TAU, WORK, INFO )
23 * .. Scalar Arguments ..
24 * INTEGER INFO, K, LDA, M, N
26 * .. Array Arguments ..
27 * COMPLEX*16 A( LDA, * ), TAU( * ), WORK( * )
36 *> ZUNGL2 generates an m-by-n complex matrix Q with orthonormal rows,
37 *> which is defined as the first m rows of a product of k elementary
38 *> reflectors of order n
40 *> Q = H(k)**H . . . H(2)**H H(1)**H
42 *> as returned by ZGELQF.
51 *> The number of rows of the matrix Q. M >= 0.
57 *> The number of columns of the matrix Q. N >= M.
63 *> The number of elementary reflectors whose product defines the
64 *> matrix Q. M >= K >= 0.
69 *> A is COMPLEX*16 array, dimension (LDA,N)
70 *> On entry, the i-th row must contain the vector which defines
71 *> the elementary reflector H(i), for i = 1,2,...,k, as returned
72 *> by ZGELQF in the first k rows of its array argument A.
73 *> On exit, the m by n matrix Q.
79 *> The first dimension of the array A. LDA >= max(1,M).
84 *> TAU is COMPLEX*16 array, dimension (K)
85 *> TAU(i) must contain the scalar factor of the elementary
86 *> reflector H(i), as returned by ZGELQF.
91 *> WORK is COMPLEX*16 array, dimension (M)
97 *> = 0: successful exit
98 *> < 0: if INFO = -i, the i-th argument has an illegal value
104 *> \author Univ. of Tennessee
105 *> \author Univ. of California Berkeley
106 *> \author Univ. of Colorado Denver
109 *> \date September 2012
111 *> \ingroup complex16OTHERcomputational
113 * =====================================================================
114 SUBROUTINE ZUNGL2( M, N, K, A, LDA, TAU, WORK, INFO )
116 * -- LAPACK computational routine (version 3.4.2) --
117 * -- LAPACK is a software package provided by Univ. of Tennessee, --
118 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
121 * .. Scalar Arguments ..
122 INTEGER INFO, K, LDA, M, N
124 * .. Array Arguments ..
125 COMPLEX*16 A( LDA, * ), TAU( * ), WORK( * )
128 * =====================================================================
132 PARAMETER ( ONE = ( 1.0D+0, 0.0D+0 ),
133 $ ZERO = ( 0.0D+0, 0.0D+0 ) )
135 * .. Local Scalars ..
138 * .. External Subroutines ..
139 EXTERNAL XERBLA, ZLACGV, ZLARF, ZSCAL
141 * .. Intrinsic Functions ..
142 INTRINSIC DCONJG, MAX
144 * .. Executable Statements ..
146 * Test the input arguments
151 ELSE IF( N.LT.M ) THEN
153 ELSE IF( K.LT.0 .OR. K.GT.M ) THEN
155 ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
159 CALL XERBLA( 'ZUNGL2', -INFO )
163 * Quick return if possible
170 * Initialise rows k+1:m to rows of the unit matrix
176 IF( J.GT.K .AND. J.LE.M )
183 * Apply H(i)**H to A(i:m,i:n) from the right
186 CALL ZLACGV( N-I, A( I, I+1 ), LDA )
189 CALL ZLARF( 'Right', M-I, N-I+1, A( I, I ), LDA,
190 $ DCONJG( TAU( I ) ), A( I+1, I ), LDA, WORK )
192 CALL ZSCAL( N-I, -TAU( I ), A( I, I+1 ), LDA )
193 CALL ZLACGV( N-I, A( I, I+1 ), LDA )
195 A( I, I ) = ONE - DCONJG( TAU( I ) )
197 * Set A(i,1:i-1) to zero