Annotation of rpl/lapack/lapack/dgeql2.f, revision 1.17
1.13 bertrand 1: *> \brief \b DGEQL2 computes the QL factorization of a general rectangular matrix using an unblocked algorithm.
1.10 bertrand 2: *
3: * =========== DOCUMENTATION ===========
4: *
1.17 ! bertrand 5: * Online html documentation available at
! 6: * http://www.netlib.org/lapack/explore-html/
1.10 bertrand 7: *
8: *> \htmlonly
1.17 ! bertrand 9: *> Download DGEQL2 + dependencies
! 10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dgeql2.f">
! 11: *> [TGZ]</a>
! 12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dgeql2.f">
! 13: *> [ZIP]</a>
! 14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dgeql2.f">
1.10 bertrand 15: *> [TXT]</a>
1.17 ! bertrand 16: *> \endhtmlonly
1.10 bertrand 17: *
18: * Definition:
19: * ===========
20: *
21: * SUBROUTINE DGEQL2( M, N, A, LDA, TAU, WORK, INFO )
1.17 ! bertrand 22: *
1.10 bertrand 23: * .. Scalar Arguments ..
24: * INTEGER INFO, LDA, M, N
25: * ..
26: * .. Array Arguments ..
27: * DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( * )
28: * ..
1.17 ! bertrand 29: *
1.10 bertrand 30: *
31: *> \par Purpose:
32: * =============
33: *>
34: *> \verbatim
35: *>
36: *> DGEQL2 computes a QL factorization of a real m by n matrix A:
37: *> A = Q * L.
38: *> \endverbatim
39: *
40: * Arguments:
41: * ==========
42: *
43: *> \param[in] M
44: *> \verbatim
45: *> M is INTEGER
46: *> The number of rows of the matrix A. M >= 0.
47: *> \endverbatim
48: *>
49: *> \param[in] N
50: *> \verbatim
51: *> N is INTEGER
52: *> The number of columns of the matrix A. N >= 0.
53: *> \endverbatim
54: *>
55: *> \param[in,out] A
56: *> \verbatim
57: *> A is DOUBLE PRECISION array, dimension (LDA,N)
58: *> On entry, the m by n matrix A.
59: *> On exit, if m >= n, the lower triangle of the subarray
60: *> A(m-n+1:m,1:n) contains the n by n lower triangular matrix L;
61: *> if m <= n, the elements on and below the (n-m)-th
62: *> superdiagonal contain the m by n lower trapezoidal matrix L;
63: *> the remaining elements, with the array TAU, represent the
64: *> orthogonal matrix Q as a product of elementary reflectors
65: *> (see Further Details).
66: *> \endverbatim
67: *>
68: *> \param[in] LDA
69: *> \verbatim
70: *> LDA is INTEGER
71: *> The leading dimension of the array A. LDA >= max(1,M).
72: *> \endverbatim
73: *>
74: *> \param[out] TAU
75: *> \verbatim
76: *> TAU is DOUBLE PRECISION array, dimension (min(M,N))
77: *> The scalar factors of the elementary reflectors (see Further
78: *> Details).
79: *> \endverbatim
80: *>
81: *> \param[out] WORK
82: *> \verbatim
83: *> WORK is DOUBLE PRECISION array, dimension (N)
84: *> \endverbatim
85: *>
86: *> \param[out] INFO
87: *> \verbatim
88: *> INFO is INTEGER
89: *> = 0: successful exit
90: *> < 0: if INFO = -i, the i-th argument had an illegal value
91: *> \endverbatim
92: *
93: * Authors:
94: * ========
95: *
1.17 ! bertrand 96: *> \author Univ. of Tennessee
! 97: *> \author Univ. of California Berkeley
! 98: *> \author Univ. of Colorado Denver
! 99: *> \author NAG Ltd.
1.10 bertrand 100: *
1.17 ! bertrand 101: *> \date December 2016
1.10 bertrand 102: *
103: *> \ingroup doubleGEcomputational
104: *
105: *> \par Further Details:
106: * =====================
107: *>
108: *> \verbatim
109: *>
110: *> The matrix Q is represented as a product of elementary reflectors
111: *>
112: *> Q = H(k) . . . H(2) H(1), where k = min(m,n).
113: *>
114: *> Each H(i) has the form
115: *>
116: *> H(i) = I - tau * v * v**T
117: *>
118: *> where tau is a real scalar, and v is a real vector with
119: *> v(m-k+i+1:m) = 0 and v(m-k+i) = 1; v(1:m-k+i-1) is stored on exit in
120: *> A(1:m-k+i-1,n-k+i), and tau in TAU(i).
121: *> \endverbatim
122: *>
123: * =====================================================================
1.1 bertrand 124: SUBROUTINE DGEQL2( M, N, A, LDA, TAU, WORK, INFO )
125: *
1.17 ! bertrand 126: * -- LAPACK computational routine (version 3.7.0) --
1.1 bertrand 127: * -- LAPACK is a software package provided by Univ. of Tennessee, --
128: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.17 ! bertrand 129: * December 2016
1.1 bertrand 130: *
131: * .. Scalar Arguments ..
132: INTEGER INFO, LDA, M, N
133: * ..
134: * .. Array Arguments ..
135: DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( * )
136: * ..
137: *
138: * =====================================================================
139: *
140: * .. Parameters ..
141: DOUBLE PRECISION ONE
142: PARAMETER ( ONE = 1.0D+0 )
143: * ..
144: * .. Local Scalars ..
145: INTEGER I, K
146: DOUBLE PRECISION AII
147: * ..
148: * .. External Subroutines ..
1.5 bertrand 149: EXTERNAL DLARF, DLARFG, XERBLA
1.1 bertrand 150: * ..
151: * .. Intrinsic Functions ..
152: INTRINSIC MAX, MIN
153: * ..
154: * .. Executable Statements ..
155: *
156: * Test the input arguments
157: *
158: INFO = 0
159: IF( M.LT.0 ) THEN
160: INFO = -1
161: ELSE IF( N.LT.0 ) THEN
162: INFO = -2
163: ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
164: INFO = -4
165: END IF
166: IF( INFO.NE.0 ) THEN
167: CALL XERBLA( 'DGEQL2', -INFO )
168: RETURN
169: END IF
170: *
171: K = MIN( M, N )
172: *
173: DO 10 I = K, 1, -1
174: *
175: * Generate elementary reflector H(i) to annihilate
176: * A(1:m-k+i-1,n-k+i)
177: *
1.5 bertrand 178: CALL DLARFG( M-K+I, A( M-K+I, N-K+I ), A( 1, N-K+I ), 1,
1.1 bertrand 179: $ TAU( I ) )
180: *
181: * Apply H(i) to A(1:m-k+i,1:n-k+i-1) from the left
182: *
183: AII = A( M-K+I, N-K+I )
184: A( M-K+I, N-K+I ) = ONE
185: CALL DLARF( 'Left', M-K+I, N-K+I-1, A( 1, N-K+I ), 1, TAU( I ),
186: $ A, LDA, WORK )
187: A( M-K+I, N-K+I ) = AII
188: 10 CONTINUE
189: RETURN
190: *
191: * End of DGEQL2
192: *
193: END
CVSweb interface <joel.bertrand@systella.fr>
![[BACK]](/cvsweb/icons/back.gif){kind=icon}
Return to dgeql2.f CVS log ![[TXT]](/cvsweb/icons/text.gif){kind=icon}
![[DIR]](/cvsweb/icons/dir.gif){kind=icon}
Up to [local] / rpl / lapack / lapack