-
Notifications
You must be signed in to change notification settings - Fork 441
/
dstedc.f
478 lines (478 loc) · 14.9 KB
/
dstedc.f
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
*> \brief \b DSTEDC
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
*> Download DSTEDC + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dstedc.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dstedc.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dstedc.f">
*> [TXT]</a>
*> \endhtmlonly
*
* Definition:
* ===========
*
* SUBROUTINE DSTEDC( COMPZ, N, D, E, Z, LDZ, WORK, LWORK, IWORK,
* LIWORK, INFO )
*
* .. Scalar Arguments ..
* CHARACTER COMPZ
* INTEGER INFO, LDZ, LIWORK, LWORK, N
* ..
* .. Array Arguments ..
* INTEGER IWORK( * )
* DOUBLE PRECISION D( * ), E( * ), WORK( * ), Z( LDZ, * )
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> DSTEDC computes all eigenvalues and, optionally, eigenvectors of a
*> symmetric tridiagonal matrix using the divide and conquer method.
*> The eigenvectors of a full or band real symmetric matrix can also be
*> found if DSYTRD or DSPTRD or DSBTRD has been used to reduce this
*> matrix to tridiagonal form.
*>
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] COMPZ
*> \verbatim
*> COMPZ is CHARACTER*1
*> = 'N': Compute eigenvalues only.
*> = 'I': Compute eigenvectors of tridiagonal matrix also.
*> = 'V': Compute eigenvectors of original dense symmetric
*> matrix also. On entry, Z contains the orthogonal
*> matrix used to reduce the original matrix to
*> tridiagonal form.
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> The dimension of the symmetric tridiagonal matrix. N >= 0.
*> \endverbatim
*>
*> \param[in,out] D
*> \verbatim
*> D is DOUBLE PRECISION array, dimension (N)
*> On entry, the diagonal elements of the tridiagonal matrix.
*> On exit, if INFO = 0, the eigenvalues in ascending order.
*> \endverbatim
*>
*> \param[in,out] E
*> \verbatim
*> E is DOUBLE PRECISION array, dimension (N-1)
*> On entry, the subdiagonal elements of the tridiagonal matrix.
*> On exit, E has been destroyed.
*> \endverbatim
*>
*> \param[in,out] Z
*> \verbatim
*> Z is DOUBLE PRECISION array, dimension (LDZ,N)
*> On entry, if COMPZ = 'V', then Z contains the orthogonal
*> matrix used in the reduction to tridiagonal form.
*> On exit, if INFO = 0, then if COMPZ = 'V', Z contains the
*> orthonormal eigenvectors of the original symmetric matrix,
*> and if COMPZ = 'I', Z contains the orthonormal eigenvectors
*> of the symmetric tridiagonal matrix.
*> If COMPZ = 'N', then Z is not referenced.
*> \endverbatim
*>
*> \param[in] LDZ
*> \verbatim
*> LDZ is INTEGER
*> The leading dimension of the array Z. LDZ >= 1.
*> If eigenvectors are desired, then LDZ >= max(1,N).
*> \endverbatim
*>
*> \param[out] WORK
*> \verbatim
*> WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))
*> On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
*> \endverbatim
*>
*> \param[in] LWORK
*> \verbatim
*> LWORK is INTEGER
*> The dimension of the array WORK.
*> If COMPZ = 'N' or N <= 1 then LWORK must be at least 1.
*> If COMPZ = 'V' and N > 1 then LWORK must be at least
*> ( 1 + 3*N + 2*N*lg N + 4*N**2 ),
*> where lg( N ) = smallest integer k such
*> that 2**k >= N.
*> If COMPZ = 'I' and N > 1 then LWORK must be at least
*> ( 1 + 4*N + N**2 ).
*> Note that for COMPZ = 'I' or 'V', then if N is less than or
*> equal to the minimum divide size, usually 25, then LWORK need
*> only be max(1,2*(N-1)).
*>
*> If LWORK = -1, then a workspace query is assumed; the routine
*> only calculates the optimal size of the WORK array, returns
*> this value as the first entry of the WORK array, and no error
*> message related to LWORK is issued by XERBLA.
*> \endverbatim
*>
*> \param[out] IWORK
*> \verbatim
*> IWORK is INTEGER array, dimension (MAX(1,LIWORK))
*> On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.
*> \endverbatim
*>
*> \param[in] LIWORK
*> \verbatim
*> LIWORK is INTEGER
*> The dimension of the array IWORK.
*> If COMPZ = 'N' or N <= 1 then LIWORK must be at least 1.
*> If COMPZ = 'V' and N > 1 then LIWORK must be at least
*> ( 6 + 6*N + 5*N*lg N ).
*> If COMPZ = 'I' and N > 1 then LIWORK must be at least
*> ( 3 + 5*N ).
*> Note that for COMPZ = 'I' or 'V', then if N is less than or
*> equal to the minimum divide size, usually 25, then LIWORK
*> need only be 1.
*>
*> If LIWORK = -1, then a workspace query is assumed; the
*> routine only calculates the optimal size of the IWORK array,
*> returns this value as the first entry of the IWORK array, and
*> no error message related to LIWORK is issued by XERBLA.
*> \endverbatim
*>
*> \param[out] INFO
*> \verbatim
*> INFO is INTEGER
*> = 0: successful exit.
*> < 0: if INFO = -i, the i-th argument had an illegal value.
*> > 0: The algorithm failed to compute an eigenvalue while
*> working on the submatrix lying in rows and columns
*> INFO/(N+1) through mod(INFO,N+1).
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup stedc
*
*> \par Contributors:
* ==================
*>
*> Jeff Rutter, Computer Science Division, University of California
*> at Berkeley, USA \n
*> Modified by Francoise Tisseur, University of Tennessee
*>
* =====================================================================
SUBROUTINE DSTEDC( COMPZ, N, D, E, Z, LDZ, WORK, LWORK, IWORK,
$ LIWORK, INFO )
*
* -- LAPACK computational routine --
* -- LAPACK is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
* .. Scalar Arguments ..
CHARACTER COMPZ
INTEGER INFO, LDZ, LIWORK, LWORK, N
* ..
* .. Array Arguments ..
INTEGER IWORK( * )
DOUBLE PRECISION D( * ), E( * ), WORK( * ), Z( LDZ, * )
* ..
*
* =====================================================================
*
* .. Parameters ..
DOUBLE PRECISION ZERO, ONE, TWO
PARAMETER ( ZERO = 0.0D0, ONE = 1.0D0, TWO = 2.0D0 )
* ..
* .. Local Scalars ..
LOGICAL LQUERY
INTEGER FINISH, I, ICOMPZ, II, J, K, LGN, LIWMIN,
$ LWMIN, M, SMLSIZ, START, STOREZ, STRTRW
DOUBLE PRECISION EPS, ORGNRM, P, TINY
* ..
* .. External Functions ..
LOGICAL LSAME
INTEGER ILAENV
DOUBLE PRECISION DLAMCH, DLANST
EXTERNAL LSAME, ILAENV, DLAMCH, DLANST
* ..
* .. External Subroutines ..
EXTERNAL DGEMM, DLACPY, DLAED0, DLASCL, DLASET,
$ DLASRT,
$ DSTEQR, DSTERF, DSWAP, XERBLA
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS, DBLE, INT, LOG, MAX, MOD, SQRT
* ..
* .. Executable Statements ..
*
* Test the input parameters.
*
INFO = 0
LQUERY = ( LWORK.EQ.-1 .OR. LIWORK.EQ.-1 )
*
IF( LSAME( COMPZ, 'N' ) ) THEN
ICOMPZ = 0
ELSE IF( LSAME( COMPZ, 'V' ) ) THEN
ICOMPZ = 1
ELSE IF( LSAME( COMPZ, 'I' ) ) THEN
ICOMPZ = 2
ELSE
ICOMPZ = -1
END IF
IF( ICOMPZ.LT.0 ) THEN
INFO = -1
ELSE IF( N.LT.0 ) THEN
INFO = -2
ELSE IF( ( LDZ.LT.1 ) .OR.
$ ( ICOMPZ.GT.0 .AND. LDZ.LT.MAX( 1, N ) ) ) THEN
INFO = -6
END IF
*
IF( INFO.EQ.0 ) THEN
*
* Compute the workspace requirements
*
SMLSIZ = ILAENV( 9, 'DSTEDC', ' ', 0, 0, 0, 0 )
IF( N.LE.1 .OR. ICOMPZ.EQ.0 ) THEN
LIWMIN = 1
LWMIN = 1
ELSE IF( N.LE.SMLSIZ ) THEN
LIWMIN = 1
LWMIN = 2*( N - 1 )
ELSE
LGN = INT( LOG( DBLE( N ) )/LOG( TWO ) )
IF( 2**LGN.LT.N )
$ LGN = LGN + 1
IF( 2**LGN.LT.N )
$ LGN = LGN + 1
IF( ICOMPZ.EQ.1 ) THEN
LWMIN = 1 + 3*N + 2*N*LGN + 4*N**2
LIWMIN = 6 + 6*N + 5*N*LGN
ELSE IF( ICOMPZ.EQ.2 ) THEN
LWMIN = 1 + 4*N + N**2
LIWMIN = 3 + 5*N
END IF
END IF
WORK( 1 ) = LWMIN
IWORK( 1 ) = LIWMIN
*
IF( LWORK.LT.LWMIN .AND. .NOT. LQUERY ) THEN
INFO = -8
ELSE IF( LIWORK.LT.LIWMIN .AND. .NOT. LQUERY ) THEN
INFO = -10
END IF
END IF
*
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'DSTEDC', -INFO )
RETURN
ELSE IF (LQUERY) THEN
RETURN
END IF
*
* Quick return if possible
*
IF( N.EQ.0 )
$ RETURN
IF( N.EQ.1 ) THEN
IF( ICOMPZ.NE.0 )
$ Z( 1, 1 ) = ONE
RETURN
END IF
*
* If the following conditional clause is removed, then the routine
* will use the Divide and Conquer routine to compute only the
* eigenvalues, which requires (3N + 3N**2) real workspace and
* (2 + 5N + 2N lg(N)) integer workspace.
* Since on many architectures DSTERF is much faster than any other
* algorithm for finding eigenvalues only, it is used here
* as the default. If the conditional clause is removed, then
* information on the size of workspace needs to be changed.
*
* If COMPZ = 'N', use DSTERF to compute the eigenvalues.
*
IF( ICOMPZ.EQ.0 ) THEN
CALL DSTERF( N, D, E, INFO )
GO TO 50
END IF
*
* If N is smaller than the minimum divide size (SMLSIZ+1), then
* solve the problem with another solver.
*
IF( N.LE.SMLSIZ ) THEN
*
CALL DSTEQR( COMPZ, N, D, E, Z, LDZ, WORK, INFO )
*
ELSE
*
* If COMPZ = 'V', the Z matrix must be stored elsewhere for later
* use.
*
IF( ICOMPZ.EQ.1 ) THEN
STOREZ = 1 + N*N
ELSE
STOREZ = 1
END IF
*
IF( ICOMPZ.EQ.2 ) THEN
CALL DLASET( 'Full', N, N, ZERO, ONE, Z, LDZ )
END IF
*
* Scale.
*
ORGNRM = DLANST( 'M', N, D, E )
IF( ORGNRM.EQ.ZERO )
$ GO TO 50
*
EPS = DLAMCH( 'Epsilon' )
*
START = 1
*
* while ( START <= N )
*
10 CONTINUE
IF( START.LE.N ) THEN
*
* Let FINISH be the position of the next subdiagonal entry
* such that E( FINISH ) <= TINY or FINISH = N if no such
* subdiagonal exists. The matrix identified by the elements
* between START and FINISH constitutes an independent
* sub-problem.
*
FINISH = START
20 CONTINUE
IF( FINISH.LT.N ) THEN
TINY = EPS*SQRT( ABS( D( FINISH ) ) )*
$ SQRT( ABS( D( FINISH+1 ) ) )
IF( ABS( E( FINISH ) ).GT.TINY ) THEN
FINISH = FINISH + 1
GO TO 20
END IF
END IF
*
* (Sub) Problem determined. Compute its size and solve it.
*
M = FINISH - START + 1
IF( M.EQ.1 ) THEN
START = FINISH + 1
GO TO 10
END IF
IF( M.GT.SMLSIZ ) THEN
*
* Scale.
*
ORGNRM = DLANST( 'M', M, D( START ), E( START ) )
CALL DLASCL( 'G', 0, 0, ORGNRM, ONE, M, 1, D( START ),
$ M,
$ INFO )
CALL DLASCL( 'G', 0, 0, ORGNRM, ONE, M-1, 1,
$ E( START ),
$ M-1, INFO )
*
IF( ICOMPZ.EQ.1 ) THEN
STRTRW = 1
ELSE
STRTRW = START
END IF
CALL DLAED0( ICOMPZ, N, M, D( START ), E( START ),
$ Z( STRTRW, START ), LDZ, WORK( 1 ), N,
$ WORK( STOREZ ), IWORK, INFO )
IF( INFO.NE.0 ) THEN
INFO = ( INFO / ( M+1 )+START-1 )*( N+1 ) +
$ MOD( INFO, ( M+1 ) ) + START - 1
GO TO 50
END IF
*
* Scale back.
*
CALL DLASCL( 'G', 0, 0, ONE, ORGNRM, M, 1, D( START ),
$ M,
$ INFO )
*
ELSE
IF( ICOMPZ.EQ.1 ) THEN
*
* Since QR won't update a Z matrix which is larger than
* the length of D, we must solve the sub-problem in a
* workspace and then multiply back into Z.
*
CALL DSTEQR( 'I', M, D( START ), E( START ), WORK,
$ M,
$ WORK( M*M+1 ), INFO )
CALL DLACPY( 'A', N, M, Z( 1, START ), LDZ,
$ WORK( STOREZ ), N )
CALL DGEMM( 'N', 'N', N, M, M, ONE,
$ WORK( STOREZ ), N, WORK, M, ZERO,
$ Z( 1, START ), LDZ )
ELSE IF( ICOMPZ.EQ.2 ) THEN
CALL DSTEQR( 'I', M, D( START ), E( START ),
$ Z( START, START ), LDZ, WORK, INFO )
ELSE
CALL DSTERF( M, D( START ), E( START ), INFO )
END IF
IF( INFO.NE.0 ) THEN
INFO = START*( N+1 ) + FINISH
GO TO 50
END IF
END IF
*
START = FINISH + 1
GO TO 10
END IF
*
* endwhile
*
IF( ICOMPZ.EQ.0 ) THEN
*
* Use Quick Sort
*
CALL DLASRT( 'I', N, D, INFO )
*
ELSE
*
* Use Selection Sort to minimize swaps of eigenvectors
*
DO 40 II = 2, N
I = II - 1
K = I
P = D( I )
DO 30 J = II, N
IF( D( J ).LT.P ) THEN
K = J
P = D( J )
END IF
30 CONTINUE
IF( K.NE.I ) THEN
D( K ) = D( I )
D( I ) = P
CALL DSWAP( N, Z( 1, I ), 1, Z( 1, K ), 1 )
END IF
40 CONTINUE
END IF
END IF
*
50 CONTINUE
WORK( 1 ) = LWMIN
IWORK( 1 ) = LIWMIN
*
RETURN
*
* End of DSTEDC
*
END