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1: *> \brief \b ZUNG2R
2: *
3: * =========== DOCUMENTATION ===========
4: *
5: * Online html documentation available at
6: * http://www.netlib.org/lapack/explore-html/
7: *
8: *> \htmlonly
9: *> Download ZUNG2R + dependencies
10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/zung2r.f">
11: *> [TGZ]</a>
12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zung2r.f">
13: *> [ZIP]</a>
14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zung2r.f">
15: *> [TXT]</a>
16: *> \endhtmlonly
17: *
18: * Definition:
19: * ===========
20: *
21: * SUBROUTINE ZUNG2R( M, N, K, A, LDA, TAU, WORK, INFO )
22: *
23: * .. Scalar Arguments ..
24: * INTEGER INFO, K, LDA, M, N
25: * ..
26: * .. Array Arguments ..
27: * COMPLEX*16 A( LDA, * ), TAU( * ), WORK( * )
28: * ..
29: *
30: *
31: *> \par Purpose:
32: * =============
33: *>
34: *> \verbatim
35: *>
36: *> ZUNG2R generates an m by n complex matrix Q with orthonormal columns,
37: *> which is defined as the first n columns of a product of k elementary
38: *> reflectors of order m
39: *>
40: *> Q = H(1) H(2) . . . H(k)
41: *>
42: *> as returned by ZGEQRF.
43: *> \endverbatim
44: *
45: * Arguments:
46: * ==========
47: *
48: *> \param[in] M
49: *> \verbatim
50: *> M is INTEGER
51: *> The number of rows of the matrix Q. M >= 0.
52: *> \endverbatim
53: *>
54: *> \param[in] N
55: *> \verbatim
56: *> N is INTEGER
57: *> The number of columns of the matrix Q. M >= N >= 0.
58: *> \endverbatim
59: *>
60: *> \param[in] K
61: *> \verbatim
62: *> K is INTEGER
63: *> The number of elementary reflectors whose product defines the
64: *> matrix Q. N >= K >= 0.
65: *> \endverbatim
66: *>
67: *> \param[in,out] A
68: *> \verbatim
69: *> A is COMPLEX*16 array, dimension (LDA,N)
70: *> On entry, the i-th column must contain the vector which
71: *> defines the elementary reflector H(i), for i = 1,2,...,k, as
72: *> returned by ZGEQRF in the first k columns of its array
73: *> argument A.
74: *> On exit, the m by n matrix Q.
75: *> \endverbatim
76: *>
77: *> \param[in] LDA
78: *> \verbatim
79: *> LDA is INTEGER
80: *> The first dimension of the array A. LDA >= max(1,M).
81: *> \endverbatim
82: *>
83: *> \param[in] TAU
84: *> \verbatim
85: *> TAU is COMPLEX*16 array, dimension (K)
86: *> TAU(i) must contain the scalar factor of the elementary
87: *> reflector H(i), as returned by ZGEQRF.
88: *> \endverbatim
89: *>
90: *> \param[out] WORK
91: *> \verbatim
92: *> WORK is COMPLEX*16 array, dimension (N)
93: *> \endverbatim
94: *>
95: *> \param[out] INFO
96: *> \verbatim
97: *> INFO is INTEGER
98: *> = 0: successful exit
99: *> < 0: if INFO = -i, the i-th argument has an illegal value
100: *> \endverbatim
101: *
102: * Authors:
103: * ========
104: *
105: *> \author Univ. of Tennessee
106: *> \author Univ. of California Berkeley
107: *> \author Univ. of Colorado Denver
108: *> \author NAG Ltd.
109: *
110: *> \date November 2011
111: *
112: *> \ingroup complex16OTHERcomputational
113: *
114: * =====================================================================
115: SUBROUTINE ZUNG2R( M, N, K, A, LDA, TAU, WORK, INFO )
116: *
117: * -- LAPACK computational routine (version 3.4.0) --
118: * -- LAPACK is a software package provided by Univ. of Tennessee, --
119: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
120: * November 2011
121: *
122: * .. Scalar Arguments ..
123: INTEGER INFO, K, LDA, M, N
124: * ..
125: * .. Array Arguments ..
126: COMPLEX*16 A( LDA, * ), TAU( * ), WORK( * )
127: * ..
128: *
129: * =====================================================================
130: *
131: * .. Parameters ..
132: COMPLEX*16 ONE, ZERO
133: PARAMETER ( ONE = ( 1.0D+0, 0.0D+0 ),
134: $ ZERO = ( 0.0D+0, 0.0D+0 ) )
135: * ..
136: * .. Local Scalars ..
137: INTEGER I, J, L
138: * ..
139: * .. External Subroutines ..
140: EXTERNAL XERBLA, ZLARF, ZSCAL
141: * ..
142: * .. Intrinsic Functions ..
143: INTRINSIC MAX
144: * ..
145: * .. Executable Statements ..
146: *
147: * Test the input arguments
148: *
149: INFO = 0
150: IF( M.LT.0 ) THEN
151: INFO = -1
152: ELSE IF( N.LT.0 .OR. N.GT.M ) THEN
153: INFO = -2
154: ELSE IF( K.LT.0 .OR. K.GT.N ) THEN
155: INFO = -3
156: ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
157: INFO = -5
158: END IF
159: IF( INFO.NE.0 ) THEN
160: CALL XERBLA( 'ZUNG2R', -INFO )
161: RETURN
162: END IF
163: *
164: * Quick return if possible
165: *
166: IF( N.LE.0 )
167: $ RETURN
168: *
169: * Initialise columns k+1:n to columns of the unit matrix
170: *
171: DO 20 J = K + 1, N
172: DO 10 L = 1, M
173: A( L, J ) = ZERO
174: 10 CONTINUE
175: A( J, J ) = ONE
176: 20 CONTINUE
177: *
178: DO 40 I = K, 1, -1
179: *
180: * Apply H(i) to A(i:m,i:n) from the left
181: *
182: IF( I.LT.N ) THEN
183: A( I, I ) = ONE
184: CALL ZLARF( 'Left', M-I+1, N-I, A( I, I ), 1, TAU( I ),
185: $ A( I, I+1 ), LDA, WORK )
186: END IF
187: IF( I.LT.M )
188: $ CALL ZSCAL( M-I, -TAU( I ), A( I+1, I ), 1 )
189: A( I, I ) = ONE - TAU( I )
190: *
191: * Set A(1:i-1,i) to zero
192: *
193: DO 30 L = 1, I - 1
194: A( L, I ) = ZERO
195: 30 CONTINUE
196: 40 CONTINUE
197: RETURN
198: *
199: * End of ZUNG2R
200: *
201: END
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