Annotation of rpl/lapack/lapack/dgeqr.f, revision 1.3
1.1 bertrand 1: *
2: * Definition:
3: * ===========
4: *
5: * SUBROUTINE DGEQR( M, N, A, LDA, T, TSIZE, WORK, LWORK,
6: * INFO )
7: *
8: * .. Scalar Arguments ..
9: * INTEGER INFO, LDA, M, N, TSIZE, LWORK
10: * ..
11: * .. Array Arguments ..
12: * DOUBLE PRECISION A( LDA, * ), T( * ), WORK( * )
13: * ..
14: *
15: *
16: *> \par Purpose:
17: * =============
18: *>
19: *> \verbatim
20: *> DGEQR computes a QR factorization of an M-by-N matrix A.
21: *> \endverbatim
22: *
23: * Arguments:
24: * ==========
25: *
26: *> \param[in] M
27: *> \verbatim
28: *> M is INTEGER
29: *> The number of rows of the matrix A. M >= 0.
30: *> \endverbatim
31: *>
32: *> \param[in] N
33: *> \verbatim
34: *> N is INTEGER
35: *> The number of columns of the matrix A. N >= 0.
36: *> \endverbatim
37: *>
38: *> \param[in,out] A
39: *> \verbatim
40: *> A is DOUBLE PRECISION array, dimension (LDA,N)
41: *> On entry, the M-by-N matrix A.
42: *> On exit, the elements on and above the diagonal of the array
43: *> contain the min(M,N)-by-N upper trapezoidal matrix R
44: *> (R is upper triangular if M >= N);
45: *> the elements below the diagonal are used to store part of the
46: *> data structure to represent Q.
47: *> \endverbatim
48: *>
49: *> \param[in] LDA
50: *> \verbatim
51: *> LDA is INTEGER
52: *> The leading dimension of the array A. LDA >= max(1,M).
53: *> \endverbatim
54: *>
55: *> \param[out] T
56: *> \verbatim
57: *> T is DOUBLE PRECISION array, dimension (MAX(5,TSIZE))
58: *> On exit, if INFO = 0, T(1) returns optimal (or either minimal
59: *> or optimal, if query is assumed) TSIZE. See TSIZE for details.
60: *> Remaining T contains part of the data structure used to represent Q.
61: *> If one wants to apply or construct Q, then one needs to keep T
62: *> (in addition to A) and pass it to further subroutines.
63: *> \endverbatim
64: *>
65: *> \param[in] TSIZE
66: *> \verbatim
67: *> TSIZE is INTEGER
68: *> If TSIZE >= 5, the dimension of the array T.
69: *> If TSIZE = -1 or -2, then a workspace query is assumed. The routine
70: *> only calculates the sizes of the T and WORK arrays, returns these
71: *> values as the first entries of the T and WORK arrays, and no error
72: *> message related to T or WORK is issued by XERBLA.
73: *> If TSIZE = -1, the routine calculates optimal size of T for the
74: *> optimum performance and returns this value in T(1).
75: *> If TSIZE = -2, the routine calculates minimal size of T and
76: *> returns this value in T(1).
77: *> \endverbatim
78: *>
79: *> \param[out] WORK
80: *> \verbatim
81: *> (workspace) DOUBLE PRECISION array, dimension (MAX(1,LWORK))
82: *> On exit, if INFO = 0, WORK(1) contains optimal (or either minimal
83: *> or optimal, if query was assumed) LWORK.
84: *> See LWORK for details.
85: *> \endverbatim
86: *>
87: *> \param[in] LWORK
88: *> \verbatim
89: *> LWORK is INTEGER
90: *> The dimension of the array WORK.
91: *> If LWORK = -1 or -2, then a workspace query is assumed. The routine
92: *> only calculates the sizes of the T and WORK arrays, returns these
93: *> values as the first entries of the T and WORK arrays, and no error
94: *> message related to T or WORK is issued by XERBLA.
95: *> If LWORK = -1, the routine calculates optimal size of WORK for the
96: *> optimal performance and returns this value in WORK(1).
97: *> If LWORK = -2, the routine calculates minimal size of WORK and
98: *> returns this value in WORK(1).
99: *> \endverbatim
100: *>
101: *> \param[out] INFO
102: *> \verbatim
103: *> INFO is INTEGER
104: *> = 0: successful exit
105: *> < 0: if INFO = -i, the i-th argument had an illegal value
106: *> \endverbatim
107: *
108: * Authors:
109: * ========
110: *
111: *> \author Univ. of Tennessee
112: *> \author Univ. of California Berkeley
113: *> \author Univ. of Colorado Denver
114: *> \author NAG Ltd.
115: *
116: *> \par Further Details
117: * ====================
118: *>
119: *> \verbatim
120: *>
121: *> The goal of the interface is to give maximum freedom to the developers for
122: *> creating any QR factorization algorithm they wish. The triangular
123: *> (trapezoidal) R has to be stored in the upper part of A. The lower part of A
124: *> and the array T can be used to store any relevant information for applying or
125: *> constructing the Q factor. The WORK array can safely be discarded after exit.
126: *>
127: *> Caution: One should not expect the sizes of T and WORK to be the same from one
128: *> LAPACK implementation to the other, or even from one execution to the other.
129: *> A workspace query (for T and WORK) is needed at each execution. However,
130: *> for a given execution, the size of T and WORK are fixed and will not change
131: *> from one query to the next.
132: *>
133: *> \endverbatim
134: *>
135: *> \par Further Details particular to this LAPACK implementation:
136: * ==============================================================
137: *>
138: *> \verbatim
139: *>
140: *> These details are particular for this LAPACK implementation. Users should not
141: *> take them for granted. These details may change in the future, and are unlikely not
142: *> true for another LAPACK implementation. These details are relevant if one wants
143: *> to try to understand the code. They are not part of the interface.
144: *>
145: *> In this version,
146: *>
147: *> T(2): row block size (MB)
148: *> T(3): column block size (NB)
149: *> T(6:TSIZE): data structure needed for Q, computed by
150: *> DLATSQR or DGEQRT
151: *>
152: *> Depending on the matrix dimensions M and N, and row and column
153: *> block sizes MB and NB returned by ILAENV, DGEQR will use either
154: *> DLATSQR (if the matrix is tall-and-skinny) or DGEQRT to compute
155: *> the QR factorization.
156: *>
157: *> \endverbatim
158: *>
159: * =====================================================================
160: SUBROUTINE DGEQR( M, N, A, LDA, T, TSIZE, WORK, LWORK,
161: $ INFO )
162: *
163: * -- LAPACK computational routine (version 3.7.0) --
164: * -- LAPACK is a software package provided by Univ. of Tennessee, --
165: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd. --
166: * December 2016
167: *
168: * .. Scalar Arguments ..
169: INTEGER INFO, LDA, M, N, TSIZE, LWORK
170: * ..
171: * .. Array Arguments ..
172: DOUBLE PRECISION A( LDA, * ), T( * ), WORK( * )
173: * ..
174: *
175: * =====================================================================
176: *
177: * ..
178: * .. Local Scalars ..
179: LOGICAL LQUERY, LMINWS, MINT, MINW
180: INTEGER MB, NB, MINTSZ, NBLCKS
181: * ..
182: * .. External Functions ..
183: LOGICAL LSAME
184: EXTERNAL LSAME
185: * ..
186: * .. External Subroutines ..
187: EXTERNAL DLATSQR, DGEQRT, XERBLA
188: * ..
189: * .. Intrinsic Functions ..
190: INTRINSIC MAX, MIN, MOD
191: * ..
192: * .. External Functions ..
193: INTEGER ILAENV
194: EXTERNAL ILAENV
195: * ..
196: * .. Executable Statements ..
197: *
198: * Test the input arguments
199: *
200: INFO = 0
201: *
202: LQUERY = ( TSIZE.EQ.-1 .OR. TSIZE.EQ.-2 .OR.
203: $ LWORK.EQ.-1 .OR. LWORK.EQ.-2 )
204: *
205: MINT = .FALSE.
206: MINW = .FALSE.
207: IF( TSIZE.EQ.-2 .OR. LWORK.EQ.-2 ) THEN
208: IF( TSIZE.NE.-1 ) MINT = .TRUE.
209: IF( LWORK.NE.-1 ) MINW = .TRUE.
210: END IF
211: *
212: * Determine the block size
213: *
214: IF( MIN( M, N ).GT.0 ) THEN
215: MB = ILAENV( 1, 'DGEQR ', ' ', M, N, 1, -1 )
216: NB = ILAENV( 1, 'DGEQR ', ' ', M, N, 2, -1 )
217: ELSE
218: MB = M
219: NB = 1
220: END IF
221: IF( MB.GT.M .OR. MB.LE.N ) MB = M
222: IF( NB.GT.MIN( M, N ) .OR. NB.LT.1 ) NB = 1
223: MINTSZ = N + 5
224: IF( MB.GT.N .AND. M.GT.N ) THEN
225: IF( MOD( M - N, MB - N ).EQ.0 ) THEN
226: NBLCKS = ( M - N ) / ( MB - N )
227: ELSE
228: NBLCKS = ( M - N ) / ( MB - N ) + 1
229: END IF
230: ELSE
231: NBLCKS = 1
232: END IF
233: *
234: * Determine if the workspace size satisfies minimal size
235: *
236: LMINWS = .FALSE.
237: IF( ( TSIZE.LT.MAX( 1, NB*N*NBLCKS + 5 ) .OR. LWORK.LT.NB*N )
238: $ .AND. ( LWORK.GE.N ) .AND. ( TSIZE.GE.MINTSZ )
239: $ .AND. ( .NOT.LQUERY ) ) THEN
240: IF( TSIZE.LT.MAX( 1, NB*N*NBLCKS + 5 ) ) THEN
241: LMINWS = .TRUE.
242: NB = 1
243: MB = M
244: END IF
245: IF( LWORK.LT.NB*N ) THEN
246: LMINWS = .TRUE.
247: NB = 1
248: END IF
249: END IF
250: *
251: IF( M.LT.0 ) THEN
252: INFO = -1
253: ELSE IF( N.LT.0 ) THEN
254: INFO = -2
255: ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
256: INFO = -4
257: ELSE IF( TSIZE.LT.MAX( 1, NB*N*NBLCKS + 5 )
258: $ .AND. ( .NOT.LQUERY ) .AND. ( .NOT.LMINWS ) ) THEN
259: INFO = -6
260: ELSE IF( ( LWORK.LT.MAX( 1, N*NB ) ) .AND. ( .NOT.LQUERY )
261: $ .AND. ( .NOT.LMINWS ) ) THEN
262: INFO = -8
263: END IF
264: *
265: IF( INFO.EQ.0 ) THEN
266: IF( MINT ) THEN
267: T( 1 ) = MINTSZ
268: ELSE
269: T( 1 ) = NB*N*NBLCKS + 5
270: END IF
271: T( 2 ) = MB
272: T( 3 ) = NB
273: IF( MINW ) THEN
274: WORK( 1 ) = MAX( 1, N )
275: ELSE
276: WORK( 1 ) = MAX( 1, NB*N )
277: END IF
278: END IF
279: IF( INFO.NE.0 ) THEN
280: CALL XERBLA( 'DGEQR', -INFO )
281: RETURN
282: ELSE IF( LQUERY ) THEN
283: RETURN
284: END IF
285: *
286: * Quick return if possible
287: *
288: IF( MIN( M, N ).EQ.0 ) THEN
289: RETURN
290: END IF
291: *
292: * The QR Decomposition
293: *
294: IF( ( M.LE.N ) .OR. ( MB.LE.N ) .OR. ( MB.GE.M ) ) THEN
295: CALL DGEQRT( M, N, NB, A, LDA, T( 6 ), NB, WORK, INFO )
296: ELSE
297: CALL DLATSQR( M, N, MB, NB, A, LDA, T( 6 ), NB, WORK,
298: $ LWORK, INFO )
299: END IF
300: *
301: WORK( 1 ) = MAX( 1, NB*N )
302: *
303: RETURN
304: *
305: * End of DGEQR
306: *
307: END
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