Annotation of rpl/lapack/lapack/zung2r.f, revision 1.4
1.1 bertrand 1: SUBROUTINE ZUNG2R( M, N, K, 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, K, LDA, M, N
10: * ..
11: * .. Array Arguments ..
12: COMPLEX*16 A( LDA, * ), TAU( * ), WORK( * )
13: * ..
14: *
15: * Purpose
16: * =======
17: *
18: * ZUNG2R generates an m by n complex matrix Q with orthonormal columns,
19: * which is defined as the first n columns of a product of k elementary
20: * reflectors of order m
21: *
22: * Q = H(1) H(2) . . . H(k)
23: *
24: * as returned by ZGEQRF.
25: *
26: * Arguments
27: * =========
28: *
29: * M (input) INTEGER
30: * The number of rows of the matrix Q. M >= 0.
31: *
32: * N (input) INTEGER
33: * The number of columns of the matrix Q. M >= N >= 0.
34: *
35: * K (input) INTEGER
36: * The number of elementary reflectors whose product defines the
37: * matrix Q. N >= K >= 0.
38: *
39: * A (input/output) COMPLEX*16 array, dimension (LDA,N)
40: * On entry, the i-th column must contain the vector which
41: * defines the elementary reflector H(i), for i = 1,2,...,k, as
42: * returned by ZGEQRF in the first k columns of its array
43: * argument A.
44: * On exit, the m by n matrix Q.
45: *
46: * LDA (input) INTEGER
47: * The first dimension of the array A. LDA >= max(1,M).
48: *
49: * TAU (input) COMPLEX*16 array, dimension (K)
50: * TAU(i) must contain the scalar factor of the elementary
51: * reflector H(i), as returned by ZGEQRF.
52: *
53: * WORK (workspace) COMPLEX*16 array, dimension (N)
54: *
55: * INFO (output) INTEGER
56: * = 0: successful exit
57: * < 0: if INFO = -i, the i-th argument has an illegal value
58: *
59: * =====================================================================
60: *
61: * .. Parameters ..
62: COMPLEX*16 ONE, ZERO
63: PARAMETER ( ONE = ( 1.0D+0, 0.0D+0 ),
64: $ ZERO = ( 0.0D+0, 0.0D+0 ) )
65: * ..
66: * .. Local Scalars ..
67: INTEGER I, J, L
68: * ..
69: * .. External Subroutines ..
70: EXTERNAL XERBLA, ZLARF, ZSCAL
71: * ..
72: * .. Intrinsic Functions ..
73: INTRINSIC MAX
74: * ..
75: * .. Executable Statements ..
76: *
77: * Test the input arguments
78: *
79: INFO = 0
80: IF( M.LT.0 ) THEN
81: INFO = -1
82: ELSE IF( N.LT.0 .OR. N.GT.M ) THEN
83: INFO = -2
84: ELSE IF( K.LT.0 .OR. K.GT.N ) THEN
85: INFO = -3
86: ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
87: INFO = -5
88: END IF
89: IF( INFO.NE.0 ) THEN
90: CALL XERBLA( 'ZUNG2R', -INFO )
91: RETURN
92: END IF
93: *
94: * Quick return if possible
95: *
96: IF( N.LE.0 )
97: $ RETURN
98: *
99: * Initialise columns k+1:n to columns of the unit matrix
100: *
101: DO 20 J = K + 1, N
102: DO 10 L = 1, M
103: A( L, J ) = ZERO
104: 10 CONTINUE
105: A( J, J ) = ONE
106: 20 CONTINUE
107: *
108: DO 40 I = K, 1, -1
109: *
110: * Apply H(i) to A(i:m,i:n) from the left
111: *
112: IF( I.LT.N ) THEN
113: A( I, I ) = ONE
114: CALL ZLARF( 'Left', M-I+1, N-I, A( I, I ), 1, TAU( I ),
115: $ A( I, I+1 ), LDA, WORK )
116: END IF
117: IF( I.LT.M )
118: $ CALL ZSCAL( M-I, -TAU( I ), A( I+1, I ), 1 )
119: A( I, I ) = ONE - TAU( I )
120: *
121: * Set A(1:i-1,i) to zero
122: *
123: DO 30 L = 1, I - 1
124: A( L, I ) = ZERO
125: 30 CONTINUE
126: 40 CONTINUE
127: RETURN
128: *
129: * End of ZUNG2R
130: *
131: END
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