1: SUBROUTINE DORGR2( 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: DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( * )
13: * ..
14: *
15: * Purpose
16: * =======
17: *
18: * DORGR2 generates an m by n real matrix Q with orthonormal rows,
19: * which is defined as the last m rows of a product of k elementary
20: * reflectors of order n
21: *
22: * Q = H(1) H(2) . . . H(k)
23: *
24: * as returned by DGERQF.
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. N >= M.
34: *
35: * K (input) INTEGER
36: * The number of elementary reflectors whose product defines the
37: * matrix Q. M >= K >= 0.
38: *
39: * A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
40: * On entry, the (m-k+i)-th row must contain the vector which
41: * defines the elementary reflector H(i), for i = 1,2,...,k, as
42: * returned by DGERQF in the last k rows of its array argument
43: * 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) DOUBLE PRECISION array, dimension (K)
50: * TAU(i) must contain the scalar factor of the elementary
51: * reflector H(i), as returned by DGERQF.
52: *
53: * WORK (workspace) DOUBLE PRECISION array, dimension (M)
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: DOUBLE PRECISION ONE, ZERO
63: PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
64: * ..
65: * .. Local Scalars ..
66: INTEGER I, II, J, L
67: * ..
68: * .. External Subroutines ..
69: EXTERNAL DLARF, DSCAL, XERBLA
70: * ..
71: * .. Intrinsic Functions ..
72: INTRINSIC MAX
73: * ..
74: * .. Executable Statements ..
75: *
76: * Test the input arguments
77: *
78: INFO = 0
79: IF( M.LT.0 ) THEN
80: INFO = -1
81: ELSE IF( N.LT.M ) THEN
82: INFO = -2
83: ELSE IF( K.LT.0 .OR. K.GT.M ) THEN
84: INFO = -3
85: ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
86: INFO = -5
87: END IF
88: IF( INFO.NE.0 ) THEN
89: CALL XERBLA( 'DORGR2', -INFO )
90: RETURN
91: END IF
92: *
93: * Quick return if possible
94: *
95: IF( M.LE.0 )
96: $ RETURN
97: *
98: IF( K.LT.M ) THEN
99: *
100: * Initialise rows 1:m-k to rows of the unit matrix
101: *
102: DO 20 J = 1, N
103: DO 10 L = 1, M - K
104: A( L, J ) = ZERO
105: 10 CONTINUE
106: IF( J.GT.N-M .AND. J.LE.N-K )
107: $ A( M-N+J, J ) = ONE
108: 20 CONTINUE
109: END IF
110: *
111: DO 40 I = 1, K
112: II = M - K + I
113: *
114: * Apply H(i) to A(1:m-k+i,1:n-k+i) from the right
115: *
116: A( II, N-M+II ) = ONE
117: CALL DLARF( 'Right', II-1, N-M+II, A( II, 1 ), LDA, TAU( I ),
118: $ A, LDA, WORK )
119: CALL DSCAL( N-M+II-1, -TAU( I ), A( II, 1 ), LDA )
120: A( II, N-M+II ) = ONE - TAU( I )
121: *
122: * Set A(m-k+i,n-k+i+1:n) to zero
123: *
124: DO 30 L = N - M + II + 1, N
125: A( II, L ) = ZERO
126: 30 CONTINUE
127: 40 CONTINUE
128: RETURN
129: *
130: * End of DORGR2
131: *
132: END
CVSweb interface <joel.bertrand@systella.fr>