Annotation of rpl/lapack/lapack/dorm2r.f, revision 1.8
1.1 bertrand 1: SUBROUTINE DORM2R( SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC,
2: $ WORK, INFO )
3: *
1.8 ! bertrand 4: * -- LAPACK routine (version 3.3.1) --
1.1 bertrand 5: * -- LAPACK is a software package provided by Univ. of Tennessee, --
6: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.8 ! bertrand 7: * -- April 2011 --
1.1 bertrand 8: *
9: * .. Scalar Arguments ..
10: CHARACTER SIDE, TRANS
11: INTEGER INFO, K, LDA, LDC, M, N
12: * ..
13: * .. Array Arguments ..
14: DOUBLE PRECISION A( LDA, * ), C( LDC, * ), TAU( * ), WORK( * )
15: * ..
16: *
17: * Purpose
18: * =======
19: *
20: * DORM2R overwrites the general real m by n matrix C with
21: *
22: * Q * C if SIDE = 'L' and TRANS = 'N', or
23: *
1.8 ! bertrand 24: * Q**T* C if SIDE = 'L' and TRANS = 'T', or
1.1 bertrand 25: *
26: * C * Q if SIDE = 'R' and TRANS = 'N', or
27: *
1.8 ! bertrand 28: * C * Q**T if SIDE = 'R' and TRANS = 'T',
1.1 bertrand 29: *
30: * where Q is a real orthogonal matrix defined as the product of k
31: * elementary reflectors
32: *
33: * Q = H(1) H(2) . . . H(k)
34: *
35: * as returned by DGEQRF. Q is of order m if SIDE = 'L' and of order n
36: * if SIDE = 'R'.
37: *
38: * Arguments
39: * =========
40: *
41: * SIDE (input) CHARACTER*1
1.8 ! bertrand 42: * = 'L': apply Q or Q**T from the Left
! 43: * = 'R': apply Q or Q**T from the Right
1.1 bertrand 44: *
45: * TRANS (input) CHARACTER*1
46: * = 'N': apply Q (No transpose)
1.8 ! bertrand 47: * = 'T': apply Q**T (Transpose)
1.1 bertrand 48: *
49: * M (input) INTEGER
50: * The number of rows of the matrix C. M >= 0.
51: *
52: * N (input) INTEGER
53: * The number of columns of the matrix C. N >= 0.
54: *
55: * K (input) INTEGER
56: * The number of elementary reflectors whose product defines
57: * the matrix Q.
58: * If SIDE = 'L', M >= K >= 0;
59: * if SIDE = 'R', N >= K >= 0.
60: *
61: * A (input) DOUBLE PRECISION array, dimension (LDA,K)
62: * The i-th column must contain the vector which defines the
63: * elementary reflector H(i), for i = 1,2,...,k, as returned by
64: * DGEQRF in the first k columns of its array argument A.
65: * A is modified by the routine but restored on exit.
66: *
67: * LDA (input) INTEGER
68: * The leading dimension of the array A.
69: * If SIDE = 'L', LDA >= max(1,M);
70: * if SIDE = 'R', LDA >= max(1,N).
71: *
72: * TAU (input) DOUBLE PRECISION array, dimension (K)
73: * TAU(i) must contain the scalar factor of the elementary
74: * reflector H(i), as returned by DGEQRF.
75: *
76: * C (input/output) DOUBLE PRECISION array, dimension (LDC,N)
77: * On entry, the m by n matrix C.
1.8 ! bertrand 78: * On exit, C is overwritten by Q*C or Q**T*C or C*Q**T or C*Q.
1.1 bertrand 79: *
80: * LDC (input) INTEGER
81: * The leading dimension of the array C. LDC >= max(1,M).
82: *
83: * WORK (workspace) DOUBLE PRECISION array, dimension
84: * (N) if SIDE = 'L',
85: * (M) if SIDE = 'R'
86: *
87: * INFO (output) INTEGER
88: * = 0: successful exit
89: * < 0: if INFO = -i, the i-th argument had an illegal value
90: *
91: * =====================================================================
92: *
93: * .. Parameters ..
94: DOUBLE PRECISION ONE
95: PARAMETER ( ONE = 1.0D+0 )
96: * ..
97: * .. Local Scalars ..
98: LOGICAL LEFT, NOTRAN
99: INTEGER I, I1, I2, I3, IC, JC, MI, NI, NQ
100: DOUBLE PRECISION AII
101: * ..
102: * .. External Functions ..
103: LOGICAL LSAME
104: EXTERNAL LSAME
105: * ..
106: * .. External Subroutines ..
107: EXTERNAL DLARF, XERBLA
108: * ..
109: * .. Intrinsic Functions ..
110: INTRINSIC MAX
111: * ..
112: * .. Executable Statements ..
113: *
114: * Test the input arguments
115: *
116: INFO = 0
117: LEFT = LSAME( SIDE, 'L' )
118: NOTRAN = LSAME( TRANS, 'N' )
119: *
120: * NQ is the order of Q
121: *
122: IF( LEFT ) THEN
123: NQ = M
124: ELSE
125: NQ = N
126: END IF
127: IF( .NOT.LEFT .AND. .NOT.LSAME( SIDE, 'R' ) ) THEN
128: INFO = -1
129: ELSE IF( .NOT.NOTRAN .AND. .NOT.LSAME( TRANS, 'T' ) ) THEN
130: INFO = -2
131: ELSE IF( M.LT.0 ) THEN
132: INFO = -3
133: ELSE IF( N.LT.0 ) THEN
134: INFO = -4
135: ELSE IF( K.LT.0 .OR. K.GT.NQ ) THEN
136: INFO = -5
137: ELSE IF( LDA.LT.MAX( 1, NQ ) ) THEN
138: INFO = -7
139: ELSE IF( LDC.LT.MAX( 1, M ) ) THEN
140: INFO = -10
141: END IF
142: IF( INFO.NE.0 ) THEN
143: CALL XERBLA( 'DORM2R', -INFO )
144: RETURN
145: END IF
146: *
147: * Quick return if possible
148: *
149: IF( M.EQ.0 .OR. N.EQ.0 .OR. K.EQ.0 )
150: $ RETURN
151: *
152: IF( ( LEFT .AND. .NOT.NOTRAN ) .OR. ( .NOT.LEFT .AND. NOTRAN ) )
153: $ THEN
154: I1 = 1
155: I2 = K
156: I3 = 1
157: ELSE
158: I1 = K
159: I2 = 1
160: I3 = -1
161: END IF
162: *
163: IF( LEFT ) THEN
164: NI = N
165: JC = 1
166: ELSE
167: MI = M
168: IC = 1
169: END IF
170: *
171: DO 10 I = I1, I2, I3
172: IF( LEFT ) THEN
173: *
174: * H(i) is applied to C(i:m,1:n)
175: *
176: MI = M - I + 1
177: IC = I
178: ELSE
179: *
180: * H(i) is applied to C(1:m,i:n)
181: *
182: NI = N - I + 1
183: JC = I
184: END IF
185: *
186: * Apply H(i)
187: *
188: AII = A( I, I )
189: A( I, I ) = ONE
190: CALL DLARF( SIDE, MI, NI, A( I, I ), 1, TAU( I ), C( IC, JC ),
191: $ LDC, WORK )
192: A( I, I ) = AII
193: 10 CONTINUE
194: RETURN
195: *
196: * End of DORM2R
197: *
198: END
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