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
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
|
SUBROUTINE SLARRD2( RANGE, ORDER, N, VL, VU, IL, IU, GERS,
$ RELTOL, D, E, E2, PIVMIN, NSPLIT, ISPLIT,
$ M, W, WERR, WL, WU, IBLOCK, INDEXW,
$ WORK, IWORK, DOL, DOU, INFO )
*
* -- ScaLAPACK auxiliary routine (version 2.0) --
* Univ. of Tennessee, Univ. of California Berkeley, Univ. of Colorado Denver
* July 4, 2010
*
* .. Scalar Arguments ..
CHARACTER ORDER, RANGE
INTEGER DOL, DOU, IL, INFO, IU, M, N, NSPLIT
REAL PIVMIN, RELTOL, VL, VU, WL, WU
* ..
* .. Array Arguments ..
INTEGER IBLOCK( * ), INDEXW( * ),
$ ISPLIT( * ), IWORK( * )
REAL D( * ), E( * ), E2( * ),
$ GERS( * ), W( * ), WERR( * ), WORK( * )
* ..
*
* Purpose
* =======
*
* SLARRD2 computes the eigenvalues of a symmetric tridiagonal
* matrix T to limited initial accuracy. This is an auxiliary code to be
* called from SLARRE2A.
*
* SLARRD2 has been created using the LAPACK code SLARRD
* which itself stems from SSTEBZ. The motivation for creating
* SLARRD2 is efficiency: When computing eigenvalues in parallel
* and the input tridiagonal matrix splits into blocks, SLARRD2
* can skip over blocks which contain none of the eigenvalues from
* DOL to DOU for which the processor responsible. In extreme cases (such
* as large matrices consisting of many blocks of small size, e.g. 2x2,
* the gain can be substantial.
*
* Arguments
* =========
*
* RANGE (input) CHARACTER
* = 'A': ("All") all eigenvalues will be found.
* = 'V': ("Value") all eigenvalues in the half-open interval
* (VL, VU] will be found.
* = 'I': ("Index") the IL-th through IU-th eigenvalues (of the
* entire matrix) will be found.
*
* ORDER (input) CHARACTER
* = 'B': ("By Block") the eigenvalues will be grouped by
* split-off block (see IBLOCK, ISPLIT) and
* ordered from smallest to largest within
* the block.
* = 'E': ("Entire matrix")
* the eigenvalues for the entire matrix
* will be ordered from smallest to
* largest.
*
* N (input) INTEGER
* The order of the tridiagonal matrix T. N >= 0.
*
* VL (input) REAL
* VU (input) REAL
* If RANGE='V', the lower and upper bounds of the interval to
* be searched for eigenvalues. Eigenvalues less than or equal
* to VL, or greater than VU, will not be returned. VL < VU.
* Not referenced if RANGE = 'A' or 'I'.
*
* IL (input) INTEGER
* IU (input) INTEGER
* If RANGE='I', the indices (in ascending order) of the
* smallest and largest eigenvalues to be returned.
* 1 <= IL <= IU <= N, if N > 0; IL = 1 and IU = 0 if N = 0.
* Not referenced if RANGE = 'A' or 'V'.
*
* GERS (input) REAL array, dimension (2*N)
* The N Gerschgorin intervals (the i-th Gerschgorin interval
* is (GERS(2*i-1), GERS(2*i)).
*
* RELTOL (input) REAL
* The minimum relative width of an interval. When an interval
* is narrower than RELTOL times the larger (in
* magnitude) endpoint, then it is considered to be
* sufficiently small, i.e., converged. Note: this should
* always be at least radix*machine epsilon.
*
* D (input) REAL array, dimension (N)
* The n diagonal elements of the tridiagonal matrix T.
*
* E (input) REAL array, dimension (N-1)
* The (n-1) off-diagonal elements of the tridiagonal matrix T.
*
* E2 (input) REAL array, dimension (N-1)
* The (n-1) squared off-diagonal elements of the tridiagonal matrix T.
*
* PIVMIN (input) REAL
* The minimum pivot allowed in the sturm sequence for T.
*
* NSPLIT (input) INTEGER
* The number of diagonal blocks in the matrix T.
* 1 <= NSPLIT <= N.
*
* ISPLIT (input) INTEGER array, dimension (N)
* The splitting points, at which T breaks up into submatrices.
* The first submatrix consists of rows/columns 1 to ISPLIT(1),
* the second of rows/columns ISPLIT(1)+1 through ISPLIT(2),
* etc., and the NSPLIT-th consists of rows/columns
* ISPLIT(NSPLIT-1)+1 through ISPLIT(NSPLIT)=N.
* (Only the first NSPLIT elements will actually be used, but
* since the user cannot know a priori what value NSPLIT will
* have, N words must be reserved for ISPLIT.)
*
* M (output) INTEGER
* The actual number of eigenvalues found. 0 <= M <= N.
* (See also the description of INFO=2,3.)
*
* W (output) REAL array, dimension (N)
* On exit, the first M elements of W will contain the
* eigenvalue approximations. SLARRD2 computes an interval
* I_j = (a_j, b_j] that includes eigenvalue j. The eigenvalue
* approximation is given as the interval midpoint
* W(j)= ( a_j + b_j)/2. The corresponding error is bounded by
* WERR(j) = abs( a_j - b_j)/2
*
* WERR (output) REAL array, dimension (N)
* The error bound on the corresponding eigenvalue approximation
* in W.
*
* WL (output) REAL
* WU (output) REAL
* The interval (WL, WU] contains all the wanted eigenvalues.
* If RANGE='V', then WL=VL and WU=VU.
* If RANGE='A', then WL and WU are the global Gerschgorin bounds
* on the spectrum.
* If RANGE='I', then WL and WU are computed by SLAEBZ from the
* index range specified.
*
* IBLOCK (output) INTEGER array, dimension (N)
* At each row/column j where E(j) is zero or small, the
* matrix T is considered to split into a block diagonal
* matrix. On exit, if INFO = 0, IBLOCK(i) specifies to which
* block (from 1 to the number of blocks) the eigenvalue W(i)
* belongs. (SLARRD2 may use the remaining N-M elements as
* workspace.)
*
* INDEXW (output) INTEGER array, dimension (N)
* The indices of the eigenvalues within each block (submatrix);
* for example, INDEXW(i)= j and IBLOCK(i)=k imply that the
* i-th eigenvalue W(i) is the j-th eigenvalue in block k.
*
* WORK (workspace) REAL array, dimension (4*N)
*
* IWORK (workspace) INTEGER array, dimension (3*N)
*
* DOL (input) INTEGER
* DOU (input) INTEGER
* If the user wants to work on only a selected part of the
* representation tree, he can specify an index range DOL:DOU.
* Otherwise, the setting DOL=1, DOU=N should be applied.
* Note that DOL and DOU refer to the order in which the eigenvalues
* are stored in W.
*
* INFO (output) INTEGER
* = 0: successful exit
* < 0: if INFO = -i, the i-th argument had an illegal value
* > 0: some or all of the eigenvalues failed to converge or
* were not computed:
* =1 or 3: Bisection failed to converge for some
* eigenvalues; these eigenvalues are flagged by a
* negative block number. The effect is that the
* eigenvalues may not be as accurate as the
* absolute and relative tolerances. This is
* generally caused by unexpectedly inaccurate
* arithmetic.
* =2 or 3: RANGE='I' only: Not all of the eigenvalues
* IL:IU were found.
* Effect: M < IU+1-IL
* Cause: non-monotonic arithmetic, causing the
* Sturm sequence to be non-monotonic.
* Cure: recalculate, using RANGE='A', and pick
* out eigenvalues IL:IU. In some cases,
* increasing the PARAMETER "FUDGE" may
* make things work.
* = 4: RANGE='I', and the Gershgorin interval
* initially used was too small. No eigenvalues
* were computed.
* Probable cause: your machine has sloppy
* floating-point arithmetic.
* Cure: Increase the PARAMETER "FUDGE",
* recompile, and try again.
*
* Internal Parameters
* ===================
*
* FUDGE REAL , default = 2 originally, increased to 10.
* A "fudge factor" to widen the Gershgorin intervals. Ideally,
* a value of 1 should work, but on machines with sloppy
* arithmetic, this needs to be larger. The default for
* publicly released versions should be large enough to handle
* the worst machine around. Note that this has no effect
* on accuracy of the solution.
*
* =====================================================================
*
* .. Parameters ..
REAL ZERO, ONE, TWO, HALF, FUDGE
PARAMETER ( ZERO = 0.0E0, ONE = 1.0E0,
$ TWO = 2.0E0, HALF = ONE/TWO,
$ FUDGE = 10.0E0 )
* ..
* .. Local Scalars ..
LOGICAL NCNVRG, TOOFEW
INTEGER I, IB, IBEGIN, IDISCL, IDISCU, IE, IEND, IINFO,
$ IM, IN, IOFF, IORDER, IOUT, IRANGE, ITMAX,
$ ITMP1, ITMP2, IW, IWOFF, J, JBLK, JDISC, JE,
$ JEE, NB, NWL, NWU
REAL ATOLI, EPS, GL, GU, RTOLI, SPDIAM, TMP1, TMP2,
$ TNORM, UFLOW, WKILL, WLU, WUL
* ..
* .. Local Arrays ..
INTEGER IDUMMA( 1 )
* ..
* .. External Functions ..
LOGICAL LSAME
INTEGER ILAENV
REAL SLAMCH
EXTERNAL LSAME, ILAENV, SLAMCH
* ..
* .. External Subroutines ..
EXTERNAL SLAEBZ
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS, INT, LOG, MAX, MIN, SQRT
* ..
* .. Executable Statements ..
*
INFO = 0
*
* Decode RANGE
*
IF( LSAME( RANGE, 'A' ) ) THEN
IRANGE = 1
ELSE IF( LSAME( RANGE, 'V' ) ) THEN
IRANGE = 2
ELSE IF( LSAME( RANGE, 'I' ) ) THEN
IRANGE = 3
ELSE
IRANGE = 0
END IF
*
* Decode ORDER
*
IF( LSAME( ORDER, 'B' ) ) THEN
IORDER = 2
ELSE IF( LSAME( ORDER, 'E' ) ) THEN
IORDER = 1
ELSE
IORDER = 0
END IF
*
* Check for Errors
*
IF( IRANGE.LE.0 ) THEN
INFO = -1
ELSE IF( IORDER.LE.0 ) THEN
INFO = -2
ELSE IF( N.LT.0 ) THEN
INFO = -3
ELSE IF( IRANGE.EQ.2 ) THEN
IF( VL.GE.VU )
$ INFO = -5
ELSE IF( IRANGE.EQ.3 .AND. ( IL.LT.1 .OR. IL.GT.MAX( 1, N ) ) )
$ THEN
INFO = -6
ELSE IF( IRANGE.EQ.3 .AND. ( IU.LT.MIN( N, IL ) .OR. IU.GT.N ) )
$ THEN
INFO = -7
END IF
*
IF( INFO.NE.0 ) THEN
RETURN
END IF
* Initialize error flags
INFO = 0
NCNVRG = .FALSE.
TOOFEW = .FALSE.
* Quick return if possible
M = 0
IF( N.EQ.0 ) RETURN
* Simplification:
IF( IRANGE.EQ.3 .AND. IL.EQ.1 .AND. IU.EQ.N ) IRANGE = 1
* Get machine constants
EPS = SLAMCH( 'P' )
UFLOW = SLAMCH( 'U' )
* Special Case when N=1
* Treat case of 1x1 matrix for quick return
IF( N.EQ.1 ) THEN
IF( (IRANGE.EQ.1).OR.
$ ((IRANGE.EQ.2).AND.(D(1).GT.VL).AND.(D(1).LE.VU)).OR.
$ ((IRANGE.EQ.3).AND.(IL.EQ.1).AND.(IU.EQ.1)) ) THEN
M = 1
W(1) = D(1)
* The computation error of the eigenvalue is zero
WERR(1) = ZERO
IBLOCK( 1 ) = 1
INDEXW( 1 ) = 1
ENDIF
RETURN
END IF
* NB is the minimum vector length for vector bisection, or 0
* if only scalar is to be done.
NB = ILAENV( 1, 'SSTEBZ', ' ', N, -1, -1, -1 )
IF( NB.LE.1 ) NB = 0
* Find global spectral radius
GL = D(1)
GU = D(1)
DO 5 I = 1,N
GL = MIN( GL, GERS( 2*I - 1))
GU = MAX( GU, GERS(2*I) )
5 CONTINUE
* Compute global Gerschgorin bounds and spectral diameter
TNORM = MAX( ABS( GL ), ABS( GU ) )
GL = GL - FUDGE*TNORM*EPS*N - FUDGE*TWO*PIVMIN
GU = GU + FUDGE*TNORM*EPS*N + FUDGE*TWO*PIVMIN
SPDIAM = GU - GL
* Input arguments for SLAEBZ:
* The relative tolerance. An interval (a,b] lies within
* "relative tolerance" if b-a < RELTOL*max(|a|,|b|),
RTOLI = RELTOL
ATOLI = FUDGE*TWO*UFLOW + FUDGE*TWO*PIVMIN
IF( IRANGE.EQ.3 ) THEN
* RANGE='I': Compute an interval containing eigenvalues
* IL through IU. The initial interval [GL,GU] from the global
* Gerschgorin bounds GL and GU is refined by SLAEBZ.
ITMAX = INT( ( LOG( TNORM+PIVMIN )-LOG( PIVMIN ) ) /
$ LOG( TWO ) ) + 2
WORK( N+1 ) = GL
WORK( N+2 ) = GL
WORK( N+3 ) = GU
WORK( N+4 ) = GU
WORK( N+5 ) = GL
WORK( N+6 ) = GU
IWORK( 1 ) = -1
IWORK( 2 ) = -1
IWORK( 3 ) = N + 1
IWORK( 4 ) = N + 1
IWORK( 5 ) = IL - 1
IWORK( 6 ) = IU
*
CALL SLAEBZ( 3, ITMAX, N, 2, 2, NB, ATOLI, RTOLI, PIVMIN,
$ D, E, E2, IWORK( 5 ), WORK( N+1 ), WORK( N+5 ), IOUT,
$ IWORK, W, IBLOCK, IINFO )
IF( IINFO .NE. 0 ) THEN
INFO = IINFO
RETURN
END IF
* On exit, output intervals may not be ordered by ascending negcount
IF( IWORK( 6 ).EQ.IU ) THEN
WL = WORK( N+1 )
WLU = WORK( N+3 )
NWL = IWORK( 1 )
WU = WORK( N+4 )
WUL = WORK( N+2 )
NWU = IWORK( 4 )
ELSE
WL = WORK( N+2 )
WLU = WORK( N+4 )
NWL = IWORK( 2 )
WU = WORK( N+3 )
WUL = WORK( N+1 )
NWU = IWORK( 3 )
END IF
* On exit, the interval [WL, WLU] contains a value with negcount NWL,
* and [WUL, WU] contains a value with negcount NWU.
IF( NWL.LT.0 .OR. NWL.GE.N .OR. NWU.LT.1 .OR. NWU.GT.N ) THEN
INFO = 4
RETURN
END IF
ELSEIF( IRANGE.EQ.2 ) THEN
WL = VL
WU = VU
ELSEIF( IRANGE.EQ.1 ) THEN
WL = GL
WU = GU
ENDIF
* Find Eigenvalues -- Loop Over blocks and recompute NWL and NWU.
* NWL accumulates the number of eigenvalues .le. WL,
* NWU accumulates the number of eigenvalues .le. WU
M = 0
IEND = 0
INFO = 0
NWL = 0
NWU = 0
*
DO 70 JBLK = 1, NSPLIT
IOFF = IEND
IBEGIN = IOFF + 1
IEND = ISPLIT( JBLK )
IN = IEND - IOFF
*
IF( IRANGE.EQ.1 ) THEN
IF( (IEND.LT.DOL).OR.(IBEGIN.GT.DOU) ) THEN
* the local block contains none of eigenvalues that matter
* to this processor
NWU = NWU + IN
DO 30 J = 1, IN
M = M + 1
IBLOCK( M ) = JBLK
30 CONTINUE
GO TO 70
END IF
END IF
IF( IN.EQ.1 ) THEN
* 1x1 block
IF( WL.GE.D( IBEGIN )-PIVMIN )
$ NWL = NWL + 1
IF( WU.GE.D( IBEGIN )-PIVMIN )
$ NWU = NWU + 1
IF( IRANGE.EQ.1 .OR. ( WL.LT.D( IBEGIN )-PIVMIN .AND. WU.GE.
$ D( IBEGIN )-PIVMIN ) ) THEN
M = M + 1
W( M ) = D( IBEGIN )
WERR(M) = ZERO
* The gap for a single block doesn't matter for the later
* algorithm and is assigned an arbitrary large value
IBLOCK( M ) = JBLK
INDEXW( M ) = 1
END IF
ELSE
* General Case - block of size IN > 2
* Compute local Gerschgorin interval and use it as the initial
* interval for SLAEBZ
GU = D( IBEGIN )
GL = D( IBEGIN )
TMP1 = ZERO
DO 40 J = IBEGIN, IEND
GL = MIN( GL, GERS( 2*J - 1))
GU = MAX( GU, GERS(2*J) )
40 CONTINUE
SPDIAM = GU - GL
GL = GL - FUDGE*TNORM*EPS*IN - FUDGE*PIVMIN
GU = GU + FUDGE*TNORM*EPS*IN + FUDGE*PIVMIN
*
IF( IRANGE.GT.1 ) THEN
IF( GU.LT.WL ) THEN
* the local block contains none of the wanted eigenvalues
NWL = NWL + IN
NWU = NWU + IN
GO TO 70
END IF
* refine search interval if possible, only range (WL,WU] matters
GL = MAX( GL, WL )
GU = MIN( GU, WU )
IF( GL.GE.GU )
$ GO TO 70
END IF
* Find negcount of initial interval boundaries GL and GU
WORK( N+1 ) = GL
WORK( N+IN+1 ) = GU
CALL SLAEBZ( 1, 0, IN, IN, 1, NB, ATOLI, RTOLI, PIVMIN,
$ D( IBEGIN ), E( IBEGIN ), E2( IBEGIN ),
$ IDUMMA, WORK( N+1 ), WORK( N+2*IN+1 ), IM,
$ IWORK, W( M+1 ), IBLOCK( M+1 ), IINFO )
IF( IINFO .NE. 0 ) THEN
INFO = IINFO
RETURN
END IF
*
NWL = NWL + IWORK( 1 )
NWU = NWU + IWORK( IN+1 )
IWOFF = M - IWORK( 1 )
* Compute Eigenvalues
ITMAX = INT( ( LOG( GU-GL+PIVMIN )-LOG( PIVMIN ) ) /
$ LOG( TWO ) ) + 2
CALL SLAEBZ( 2, ITMAX, IN, IN, 1, NB, ATOLI, RTOLI, PIVMIN,
$ D( IBEGIN ), E( IBEGIN ), E2( IBEGIN ),
$ IDUMMA, WORK( N+1 ), WORK( N+2*IN+1 ), IOUT,
$ IWORK, W( M+1 ), IBLOCK( M+1 ), IINFO )
IF( IINFO .NE. 0 ) THEN
INFO = IINFO
RETURN
END IF
*
* Copy eigenvalues into W and IBLOCK
* Use -JBLK for block number for unconverged eigenvalues.
* Loop over the number of output intervals from SLAEBZ
DO 60 J = 1, IOUT
* eigenvalue approximation is middle point of interval
TMP1 = HALF*( WORK( J+N )+WORK( J+IN+N ) )
* semi length of error interval
TMP2 = HALF*ABS( WORK( J+N )-WORK( J+IN+N ) )
IF( J.GT.IOUT-IINFO ) THEN
* Flag non-convergence.
NCNVRG = .TRUE.
IB = -JBLK
ELSE
IB = JBLK
END IF
DO 50 JE = IWORK( J ) + 1 + IWOFF,
$ IWORK( J+IN ) + IWOFF
W( JE ) = TMP1
WERR( JE ) = TMP2
INDEXW( JE ) = JE - IWOFF
IBLOCK( JE ) = IB
50 CONTINUE
60 CONTINUE
*
M = M + IM
END IF
70 CONTINUE
* If RANGE='I', then (WL,WU) contains eigenvalues NWL+1,...,NWU
* If NWL+1 < IL or NWU > IU, discard extra eigenvalues.
IF( IRANGE.EQ.3 ) THEN
IDISCL = IL - 1 - NWL
IDISCU = NWU - IU
*
IF( IDISCL.GT.0 ) THEN
IM = 0
DO 80 JE = 1, M
* Remove some of the smallest eigenvalues from the left so that
* at the end IDISCL =0. Move all eigenvalues up to the left.
IF( W( JE ).LE.WLU .AND. IDISCL.GT.0 ) THEN
IDISCL = IDISCL - 1
ELSE
IM = IM + 1
W( IM ) = W( JE )
WERR( IM ) = WERR( JE )
INDEXW( IM ) = INDEXW( JE )
IBLOCK( IM ) = IBLOCK( JE )
END IF
80 CONTINUE
M = IM
END IF
IF( IDISCU.GT.0 ) THEN
* Remove some of the largest eigenvalues from the right so that
* at the end IDISCU =0. Move all eigenvalues up to the left.
IM=M+1
DO 81 JE = M, 1, -1
IF( W( JE ).GE.WUL .AND. IDISCU.GT.0 ) THEN
IDISCU = IDISCU - 1
ELSE
IM = IM - 1
W( IM ) = W( JE )
WERR( IM ) = WERR( JE )
INDEXW( IM ) = INDEXW( JE )
IBLOCK( IM ) = IBLOCK( JE )
END IF
81 CONTINUE
JEE = 0
DO 82 JE = IM, M
JEE = JEE + 1
W( JEE ) = W( JE )
WERR( JEE ) = WERR( JE )
INDEXW( JEE ) = INDEXW( JE )
IBLOCK( JEE ) = IBLOCK( JE )
82 CONTINUE
M = M-IM+1
END IF
IF( IDISCL.GT.0 .OR. IDISCU.GT.0 ) THEN
* Code to deal with effects of bad arithmetic. (If N(w) is
* monotone non-decreasing, this should never happen.)
* Some low eigenvalues to be discarded are not in (WL,WLU],
* or high eigenvalues to be discarded are not in (WUL,WU]
* so just kill off the smallest IDISCL/largest IDISCU
* eigenvalues, by marking the corresponding IBLOCK = 0
IF( IDISCL.GT.0 ) THEN
WKILL = WU
DO 100 JDISC = 1, IDISCL
IW = 0
DO 90 JE = 1, M
IF( IBLOCK( JE ).NE.0 .AND.
$ ( W( JE ).LT.WKILL .OR. IW.EQ.0 ) ) THEN
IW = JE
WKILL = W( JE )
END IF
90 CONTINUE
IBLOCK( IW ) = 0
100 CONTINUE
END IF
IF( IDISCU.GT.0 ) THEN
WKILL = WL
DO 120 JDISC = 1, IDISCU
IW = 0
DO 110 JE = 1, M
IF( IBLOCK( JE ).NE.0 .AND.
$ ( W( JE ).GE.WKILL .OR. IW.EQ.0 ) ) THEN
IW = JE
WKILL = W( JE )
END IF
110 CONTINUE
IBLOCK( IW ) = 0
120 CONTINUE
END IF
* Now erase all eigenvalues with IBLOCK set to zero
IM = 0
DO 130 JE = 1, M
IF( IBLOCK( JE ).NE.0 ) THEN
IM = IM + 1
W( IM ) = W( JE )
WERR( IM ) = WERR( JE )
INDEXW( IM ) = INDEXW( JE )
IBLOCK( IM ) = IBLOCK( JE )
END IF
130 CONTINUE
M = IM
END IF
IF( IDISCL.LT.0 .OR. IDISCU.LT.0 ) THEN
TOOFEW = .TRUE.
END IF
END IF
*
IF(( IRANGE.EQ.1 .AND. M.NE.N ).OR.
$ ( IRANGE.EQ.3 .AND. M.NE.IU-IL+1 ) ) THEN
TOOFEW = .TRUE.
END IF
* If ORDER='B',(IBLOCK = 2), do nothing the eigenvalues are already sorted
* by block.
* If ORDER='E',(IBLOCK = 1), sort the eigenvalues from smallest to largest
IF( IORDER.EQ.1 .AND. NSPLIT.GT.1 ) THEN
DO 150 JE = 1, M - 1
IE = 0
TMP1 = W( JE )
DO 140 J = JE + 1, M
IF( W( J ).LT.TMP1 ) THEN
IE = J
TMP1 = W( J )
END IF
140 CONTINUE
IF( IE.NE.0 ) THEN
TMP2 = WERR( IE )
ITMP1 = IBLOCK( IE )
ITMP2 = INDEXW( IE )
W( IE ) = W( JE )
WERR( IE ) = WERR( JE )
IBLOCK( IE ) = IBLOCK( JE )
INDEXW( IE ) = INDEXW( JE )
W( JE ) = TMP1
WERR( JE ) = TMP2
IBLOCK( JE ) = ITMP1
INDEXW( JE ) = ITMP2
END IF
150 CONTINUE
END IF
*
INFO = 0
IF( NCNVRG )
$ INFO = INFO + 1
IF( TOOFEW )
$ INFO = INFO + 2
RETURN
*
* End of SLARRD2
*
END
|
