LAPACK  3.7.1
LAPACK: Linear Algebra PACKage
dsyevr.f
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1 *> \brief <b> DSYEVR computes the eigenvalues and, optionally, the left and/or right eigenvectors for SY matrices</b>
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
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15 *> [TXT]</a>
16 *> \endhtmlonly
17 *
18 * Definition:
19 * ===========
20 *
21 * SUBROUTINE DSYEVR( JOBZ, RANGE, UPLO, N, A, LDA, VL, VU, IL, IU,
22 * ABSTOL, M, W, Z, LDZ, ISUPPZ, WORK, LWORK,
23 * IWORK, LIWORK, INFO )
24 *
25 * .. Scalar Arguments ..
26 * CHARACTER JOBZ, RANGE, UPLO
27 * INTEGER IL, INFO, IU, LDA, LDZ, LIWORK, LWORK, M, N
28 * DOUBLE PRECISION ABSTOL, VL, VU
29 * ..
30 * .. Array Arguments ..
31 * INTEGER ISUPPZ( * ), IWORK( * )
32 * DOUBLE PRECISION A( LDA, * ), W( * ), WORK( * ), Z( LDZ, * )
33 * ..
34 *
35 *
36 *> \par Purpose:
37 * =============
38 *>
39 *> \verbatim
40 *>
41 *> DSYEVR computes selected eigenvalues and, optionally, eigenvectors
42 *> of a real symmetric matrix A. Eigenvalues and eigenvectors can be
43 *> selected by specifying either a range of values or a range of
44 *> indices for the desired eigenvalues.
45 *>
46 *> DSYEVR first reduces the matrix A to tridiagonal form T with a call
47 *> to DSYTRD. Then, whenever possible, DSYEVR calls DSTEMR to compute
48 *> the eigenspectrum using Relatively Robust Representations. DSTEMR
49 *> computes eigenvalues by the dqds algorithm, while orthogonal
50 *> eigenvectors are computed from various "good" L D L^T representations
51 *> (also known as Relatively Robust Representations). Gram-Schmidt
52 *> orthogonalization is avoided as far as possible. More specifically,
53 *> the various steps of the algorithm are as follows.
54 *>
55 *> For each unreduced block (submatrix) of T,
56 *> (a) Compute T - sigma I = L D L^T, so that L and D
57 *> define all the wanted eigenvalues to high relative accuracy.
58 *> This means that small relative changes in the entries of D and L
59 *> cause only small relative changes in the eigenvalues and
60 *> eigenvectors. The standard (unfactored) representation of the
61 *> tridiagonal matrix T does not have this property in general.
62 *> (b) Compute the eigenvalues to suitable accuracy.
63 *> If the eigenvectors are desired, the algorithm attains full
64 *> accuracy of the computed eigenvalues only right before
65 *> the corresponding vectors have to be computed, see steps c) and d).
66 *> (c) For each cluster of close eigenvalues, select a new
67 *> shift close to the cluster, find a new factorization, and refine
68 *> the shifted eigenvalues to suitable accuracy.
69 *> (d) For each eigenvalue with a large enough relative separation compute
70 *> the corresponding eigenvector by forming a rank revealing twisted
71 *> factorization. Go back to (c) for any clusters that remain.
72 *>
73 *> The desired accuracy of the output can be specified by the input
74 *> parameter ABSTOL.
75 *>
76 *> For more details, see DSTEMR's documentation and:
77 *> - Inderjit S. Dhillon and Beresford N. Parlett: "Multiple representations
78 *> to compute orthogonal eigenvectors of symmetric tridiagonal matrices,"
79 *> Linear Algebra and its Applications, 387(1), pp. 1-28, August 2004.
80 *> - Inderjit Dhillon and Beresford Parlett: "Orthogonal Eigenvectors and
81 *> Relative Gaps," SIAM Journal on Matrix Analysis and Applications, Vol. 25,
82 *> 2004. Also LAPACK Working Note 154.
83 *> - Inderjit Dhillon: "A new O(n^2) algorithm for the symmetric
84 *> tridiagonal eigenvalue/eigenvector problem",
85 *> Computer Science Division Technical Report No. UCB/CSD-97-971,
86 *> UC Berkeley, May 1997.
87 *>
88 *>
89 *> Note 1 : DSYEVR calls DSTEMR when the full spectrum is requested
90 *> on machines which conform to the ieee-754 floating point standard.
91 *> DSYEVR calls DSTEBZ and DSTEIN on non-ieee machines and
92 *> when partial spectrum requests are made.
93 *>
94 *> Normal execution of DSTEMR may create NaNs and infinities and
95 *> hence may abort due to a floating point exception in environments
96 *> which do not handle NaNs and infinities in the ieee standard default
97 *> manner.
98 *> \endverbatim
99 *
100 * Arguments:
101 * ==========
102 *
103 *> \param[in] JOBZ
104 *> \verbatim
105 *> JOBZ is CHARACTER*1
106 *> = 'N': Compute eigenvalues only;
107 *> = 'V': Compute eigenvalues and eigenvectors.
108 *> \endverbatim
109 *>
110 *> \param[in] RANGE
111 *> \verbatim
112 *> RANGE is CHARACTER*1
113 *> = 'A': all eigenvalues will be found.
114 *> = 'V': all eigenvalues in the half-open interval (VL,VU]
115 *> will be found.
116 *> = 'I': the IL-th through IU-th eigenvalues will be found.
117 *> For RANGE = 'V' or 'I' and IU - IL < N - 1, DSTEBZ and
118 *> DSTEIN are called
119 *> \endverbatim
120 *>
121 *> \param[in] UPLO
122 *> \verbatim
123 *> UPLO is CHARACTER*1
124 *> = 'U': Upper triangle of A is stored;
125 *> = 'L': Lower triangle of A is stored.
126 *> \endverbatim
127 *>
128 *> \param[in] N
129 *> \verbatim
130 *> N is INTEGER
131 *> The order of the matrix A. N >= 0.
132 *> \endverbatim
133 *>
134 *> \param[in,out] A
135 *> \verbatim
136 *> A is DOUBLE PRECISION array, dimension (LDA, N)
137 *> On entry, the symmetric matrix A. If UPLO = 'U', the
138 *> leading N-by-N upper triangular part of A contains the
139 *> upper triangular part of the matrix A. If UPLO = 'L',
140 *> the leading N-by-N lower triangular part of A contains
141 *> the lower triangular part of the matrix A.
142 *> On exit, the lower triangle (if UPLO='L') or the upper
143 *> triangle (if UPLO='U') of A, including the diagonal, is
144 *> destroyed.
145 *> \endverbatim
146 *>
147 *> \param[in] LDA
148 *> \verbatim
149 *> LDA is INTEGER
150 *> The leading dimension of the array A. LDA >= max(1,N).
151 *> \endverbatim
152 *>
153 *> \param[in] VL
154 *> \verbatim
155 *> VL is DOUBLE PRECISION
156 *> If RANGE='V', the lower bound of the interval to
157 *> be searched for eigenvalues. VL < VU.
158 *> Not referenced if RANGE = 'A' or 'I'.
159 *> \endverbatim
160 *>
161 *> \param[in] VU
162 *> \verbatim
163 *> VU is DOUBLE PRECISION
164 *> If RANGE='V', the upper bound of the interval to
165 *> be searched for eigenvalues. VL < VU.
166 *> Not referenced if RANGE = 'A' or 'I'.
167 *> \endverbatim
168 *>
169 *> \param[in] IL
170 *> \verbatim
171 *> IL is INTEGER
172 *> If RANGE='I', the index of the
173 *> smallest eigenvalue to be returned.
174 *> 1 <= IL <= IU <= N, if N > 0; IL = 1 and IU = 0 if N = 0.
175 *> Not referenced if RANGE = 'A' or 'V'.
176 *> \endverbatim
177 *>
178 *> \param[in] IU
179 *> \verbatim
180 *> IU is INTEGER
181 *> If RANGE='I', the index of the
182 *> largest eigenvalue to be returned.
183 *> 1 <= IL <= IU <= N, if N > 0; IL = 1 and IU = 0 if N = 0.
184 *> Not referenced if RANGE = 'A' or 'V'.
185 *> \endverbatim
186 *>
187 *> \param[in] ABSTOL
188 *> \verbatim
189 *> ABSTOL is DOUBLE PRECISION
190 *> The absolute error tolerance for the eigenvalues.
191 *> An approximate eigenvalue is accepted as converged
192 *> when it is determined to lie in an interval [a,b]
193 *> of width less than or equal to
194 *>
195 *> ABSTOL + EPS * max( |a|,|b| ) ,
196 *>
197 *> where EPS is the machine precision. If ABSTOL is less than
198 *> or equal to zero, then EPS*|T| will be used in its place,
199 *> where |T| is the 1-norm of the tridiagonal matrix obtained
200 *> by reducing A to tridiagonal form.
201 *>
202 *> See "Computing Small Singular Values of Bidiagonal Matrices
203 *> with Guaranteed High Relative Accuracy," by Demmel and
204 *> Kahan, LAPACK Working Note #3.
205 *>
206 *> If high relative accuracy is important, set ABSTOL to
207 *> DLAMCH( 'Safe minimum' ). Doing so will guarantee that
208 *> eigenvalues are computed to high relative accuracy when
209 *> possible in future releases. The current code does not
210 *> make any guarantees about high relative accuracy, but
211 *> future releases will. See J. Barlow and J. Demmel,
212 *> "Computing Accurate Eigensystems of Scaled Diagonally
213 *> Dominant Matrices", LAPACK Working Note #7, for a discussion
214 *> of which matrices define their eigenvalues to high relative
215 *> accuracy.
216 *> \endverbatim
217 *>
218 *> \param[out] M
219 *> \verbatim
220 *> M is INTEGER
221 *> The total number of eigenvalues found. 0 <= M <= N.
222 *> If RANGE = 'A', M = N, and if RANGE = 'I', M = IU-IL+1.
223 *> \endverbatim
224 *>
225 *> \param[out] W
226 *> \verbatim
227 *> W is DOUBLE PRECISION array, dimension (N)
228 *> The first M elements contain the selected eigenvalues in
229 *> ascending order.
230 *> \endverbatim
231 *>
232 *> \param[out] Z
233 *> \verbatim
234 *> Z is DOUBLE PRECISION array, dimension (LDZ, max(1,M))
235 *> If JOBZ = 'V', then if INFO = 0, the first M columns of Z
236 *> contain the orthonormal eigenvectors of the matrix A
237 *> corresponding to the selected eigenvalues, with the i-th
238 *> column of Z holding the eigenvector associated with W(i).
239 *> If JOBZ = 'N', then Z is not referenced.
240 *> Note: the user must ensure that at least max(1,M) columns are
241 *> supplied in the array Z; if RANGE = 'V', the exact value of M
242 *> is not known in advance and an upper bound must be used.
243 *> Supplying N columns is always safe.
244 *> \endverbatim
245 *>
246 *> \param[in] LDZ
247 *> \verbatim
248 *> LDZ is INTEGER
249 *> The leading dimension of the array Z. LDZ >= 1, and if
250 *> JOBZ = 'V', LDZ >= max(1,N).
251 *> \endverbatim
252 *>
253 *> \param[out] ISUPPZ
254 *> \verbatim
255 *> ISUPPZ is INTEGER array, dimension ( 2*max(1,M) )
256 *> The support of the eigenvectors in Z, i.e., the indices
257 *> indicating the nonzero elements in Z. The i-th eigenvector
258 *> is nonzero only in elements ISUPPZ( 2*i-1 ) through
259 *> ISUPPZ( 2*i ). This is an output of DSTEMR (tridiagonal
260 *> matrix). The support of the eigenvectors of A is typically
261 *> 1:N because of the orthogonal transformations applied by DORMTR.
262 *> Implemented only for RANGE = 'A' or 'I' and IU - IL = N - 1
263 *> \endverbatim
264 *>
265 *> \param[out] WORK
266 *> \verbatim
267 *> WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))
268 *> On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
269 *> \endverbatim
270 *>
271 *> \param[in] LWORK
272 *> \verbatim
273 *> LWORK is INTEGER
274 *> The dimension of the array WORK. LWORK >= max(1,26*N).
275 *> For optimal efficiency, LWORK >= (NB+6)*N,
276 *> where NB is the max of the blocksize for DSYTRD and DORMTR
277 *> returned by ILAENV.
278 *>
279 *> If LWORK = -1, then a workspace query is assumed; the routine
280 *> only calculates the optimal size of the WORK array, returns
281 *> this value as the first entry of the WORK array, and no error
282 *> message related to LWORK is issued by XERBLA.
283 *> \endverbatim
284 *>
285 *> \param[out] IWORK
286 *> \verbatim
287 *> IWORK is INTEGER array, dimension (MAX(1,LIWORK))
288 *> On exit, if INFO = 0, IWORK(1) returns the optimal LWORK.
289 *> \endverbatim
290 *>
291 *> \param[in] LIWORK
292 *> \verbatim
293 *> LIWORK is INTEGER
294 *> The dimension of the array IWORK. LIWORK >= max(1,10*N).
295 *>
296 *> If LIWORK = -1, then a workspace query is assumed; the
297 *> routine only calculates the optimal size of the IWORK array,
298 *> returns this value as the first entry of the IWORK array, and
299 *> no error message related to LIWORK is issued by XERBLA.
300 *> \endverbatim
301 *>
302 *> \param[out] INFO
303 *> \verbatim
304 *> INFO is INTEGER
305 *> = 0: successful exit
306 *> < 0: if INFO = -i, the i-th argument had an illegal value
307 *> > 0: Internal error
308 *> \endverbatim
309 *
310 * Authors:
311 * ========
312 *
313 *> \author Univ. of Tennessee
314 *> \author Univ. of California Berkeley
315 *> \author Univ. of Colorado Denver
316 *> \author NAG Ltd.
317 *
318 *> \date June 2016
319 *
320 *> \ingroup doubleSYeigen
321 *
322 *> \par Contributors:
323 * ==================
324 *>
325 *> Inderjit Dhillon, IBM Almaden, USA \n
326 *> Osni Marques, LBNL/NERSC, USA \n
327 *> Ken Stanley, Computer Science Division, University of
328 *> California at Berkeley, USA \n
329 *> Jason Riedy, Computer Science Division, University of
330 *> California at Berkeley, USA \n
331 *>
332 * =====================================================================
333  SUBROUTINE dsyevr( JOBZ, RANGE, UPLO, N, A, LDA, VL, VU, IL, IU,
334  $ ABSTOL, M, W, Z, LDZ, ISUPPZ, WORK, LWORK,
335  $ IWORK, LIWORK, INFO )
336 *
337 * -- LAPACK driver routine (version 3.7.1) --
338 * -- LAPACK is a software package provided by Univ. of Tennessee, --
339 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
340 * June 2016
341 *
342 * .. Scalar Arguments ..
343  CHARACTER JOBZ, RANGE, UPLO
344  INTEGER IL, INFO, IU, LDA, LDZ, LIWORK, LWORK, M, N
345  DOUBLE PRECISION ABSTOL, VL, VU
346 * ..
347 * .. Array Arguments ..
348  INTEGER ISUPPZ( * ), IWORK( * )
349  DOUBLE PRECISION A( lda, * ), W( * ), WORK( * ), Z( ldz, * )
350 * ..
351 *
352 * =====================================================================
353 *
354 * .. Parameters ..
355  DOUBLE PRECISION ZERO, ONE, TWO
356  parameter( zero = 0.0d+0, one = 1.0d+0, two = 2.0d+0 )
357 * ..
358 * .. Local Scalars ..
359  LOGICAL ALLEIG, INDEIG, LOWER, LQUERY, VALEIG, WANTZ,
360  $ tryrac
361  CHARACTER ORDER
362  INTEGER I, IEEEOK, IINFO, IMAX, INDD, INDDD, INDE,
363  $ indee, indibl, indifl, indisp, indiwo, indtau,
364  $ indwk, indwkn, iscale, j, jj, liwmin,
365  $ llwork, llwrkn, lwkopt, lwmin, nb, nsplit
366  DOUBLE PRECISION ABSTLL, ANRM, BIGNUM, EPS, RMAX, RMIN, SAFMIN,
367  $ sigma, smlnum, tmp1, vll, vuu
368 * ..
369 * .. External Functions ..
370  LOGICAL LSAME
371  INTEGER ILAENV
372  DOUBLE PRECISION DLAMCH, DLANSY
373  EXTERNAL lsame, ilaenv, dlamch, dlansy
374 * ..
375 * .. External Subroutines ..
376  EXTERNAL dcopy, dormtr, dscal, dstebz, dstemr, dstein,
378 * ..
379 * .. Intrinsic Functions ..
380  INTRINSIC max, min, sqrt
381 * ..
382 * .. Executable Statements ..
383 *
384 * Test the input parameters.
385 *
386  ieeeok = ilaenv( 10, 'DSYEVR', 'N', 1, 2, 3, 4 )
387 *
388  lower = lsame( uplo, 'L' )
389  wantz = lsame( jobz, 'V' )
390  alleig = lsame( range, 'A' )
391  valeig = lsame( range, 'V' )
392  indeig = lsame( range, 'I' )
393 *
394  lquery = ( ( lwork.EQ.-1 ) .OR. ( liwork.EQ.-1 ) )
395 *
396  lwmin = max( 1, 26*n )
397  liwmin = max( 1, 10*n )
398 *
399  info = 0
400  IF( .NOT.( wantz .OR. lsame( jobz, 'N' ) ) ) THEN
401  info = -1
402  ELSE IF( .NOT.( alleig .OR. valeig .OR. indeig ) ) THEN
403  info = -2
404  ELSE IF( .NOT.( lower .OR. lsame( uplo, 'U' ) ) ) THEN
405  info = -3
406  ELSE IF( n.LT.0 ) THEN
407  info = -4
408  ELSE IF( lda.LT.max( 1, n ) ) THEN
409  info = -6
410  ELSE
411  IF( valeig ) THEN
412  IF( n.GT.0 .AND. vu.LE.vl )
413  $ info = -8
414  ELSE IF( indeig ) THEN
415  IF( il.LT.1 .OR. il.GT.max( 1, n ) ) THEN
416  info = -9
417  ELSE IF( iu.LT.min( n, il ) .OR. iu.GT.n ) THEN
418  info = -10
419  END IF
420  END IF
421  END IF
422  IF( info.EQ.0 ) THEN
423  IF( ldz.LT.1 .OR. ( wantz .AND. ldz.LT.n ) ) THEN
424  info = -15
425  ELSE IF( lwork.LT.lwmin .AND. .NOT.lquery ) THEN
426  info = -18
427  ELSE IF( liwork.LT.liwmin .AND. .NOT.lquery ) THEN
428  info = -20
429  END IF
430  END IF
431 *
432  IF( info.EQ.0 ) THEN
433  nb = ilaenv( 1, 'DSYTRD', uplo, n, -1, -1, -1 )
434  nb = max( nb, ilaenv( 1, 'DORMTR', uplo, n, -1, -1, -1 ) )
435  lwkopt = max( ( nb+1 )*n, lwmin )
436  work( 1 ) = lwkopt
437  iwork( 1 ) = liwmin
438  END IF
439 *
440  IF( info.NE.0 ) THEN
441  CALL xerbla( 'DSYEVR', -info )
442  RETURN
443  ELSE IF( lquery ) THEN
444  RETURN
445  END IF
446 *
447 * Quick return if possible
448 *
449  m = 0
450  IF( n.EQ.0 ) THEN
451  work( 1 ) = 1
452  RETURN
453  END IF
454 *
455  IF( n.EQ.1 ) THEN
456  work( 1 ) = 7
457  IF( alleig .OR. indeig ) THEN
458  m = 1
459  w( 1 ) = a( 1, 1 )
460  ELSE
461  IF( vl.LT.a( 1, 1 ) .AND. vu.GE.a( 1, 1 ) ) THEN
462  m = 1
463  w( 1 ) = a( 1, 1 )
464  END IF
465  END IF
466  IF( wantz ) THEN
467  z( 1, 1 ) = one
468  isuppz( 1 ) = 1
469  isuppz( 2 ) = 1
470  END IF
471  RETURN
472  END IF
473 *
474 * Get machine constants.
475 *
476  safmin = dlamch( 'Safe minimum' )
477  eps = dlamch( 'Precision' )
478  smlnum = safmin / eps
479  bignum = one / smlnum
480  rmin = sqrt( smlnum )
481  rmax = min( sqrt( bignum ), one / sqrt( sqrt( safmin ) ) )
482 *
483 * Scale matrix to allowable range, if necessary.
484 *
485  iscale = 0
486  abstll = abstol
487  IF (valeig) THEN
488  vll = vl
489  vuu = vu
490  END IF
491  anrm = dlansy( 'M', uplo, n, a, lda, work )
492  IF( anrm.GT.zero .AND. anrm.LT.rmin ) THEN
493  iscale = 1
494  sigma = rmin / anrm
495  ELSE IF( anrm.GT.rmax ) THEN
496  iscale = 1
497  sigma = rmax / anrm
498  END IF
499  IF( iscale.EQ.1 ) THEN
500  IF( lower ) THEN
501  DO 10 j = 1, n
502  CALL dscal( n-j+1, sigma, a( j, j ), 1 )
503  10 CONTINUE
504  ELSE
505  DO 20 j = 1, n
506  CALL dscal( j, sigma, a( 1, j ), 1 )
507  20 CONTINUE
508  END IF
509  IF( abstol.GT.0 )
510  $ abstll = abstol*sigma
511  IF( valeig ) THEN
512  vll = vl*sigma
513  vuu = vu*sigma
514  END IF
515  END IF
516 
517 * Initialize indices into workspaces. Note: The IWORK indices are
518 * used only if DSTERF or DSTEMR fail.
519 
520 * WORK(INDTAU:INDTAU+N-1) stores the scalar factors of the
521 * elementary reflectors used in DSYTRD.
522  indtau = 1
523 * WORK(INDD:INDD+N-1) stores the tridiagonal's diagonal entries.
524  indd = indtau + n
525 * WORK(INDE:INDE+N-1) stores the off-diagonal entries of the
526 * tridiagonal matrix from DSYTRD.
527  inde = indd + n
528 * WORK(INDDD:INDDD+N-1) is a copy of the diagonal entries over
529 * -written by DSTEMR (the DSTERF path copies the diagonal to W).
530  inddd = inde + n
531 * WORK(INDEE:INDEE+N-1) is a copy of the off-diagonal entries over
532 * -written while computing the eigenvalues in DSTERF and DSTEMR.
533  indee = inddd + n
534 * INDWK is the starting offset of the left-over workspace, and
535 * LLWORK is the remaining workspace size.
536  indwk = indee + n
537  llwork = lwork - indwk + 1
538 
539 * IWORK(INDIBL:INDIBL+M-1) corresponds to IBLOCK in DSTEBZ and
540 * stores the block indices of each of the M<=N eigenvalues.
541  indibl = 1
542 * IWORK(INDISP:INDISP+NSPLIT-1) corresponds to ISPLIT in DSTEBZ and
543 * stores the starting and finishing indices of each block.
544  indisp = indibl + n
545 * IWORK(INDIFL:INDIFL+N-1) stores the indices of eigenvectors
546 * that corresponding to eigenvectors that fail to converge in
547 * DSTEIN. This information is discarded; if any fail, the driver
548 * returns INFO > 0.
549  indifl = indisp + n
550 * INDIWO is the offset of the remaining integer workspace.
551  indiwo = indifl + n
552 
553 *
554 * Call DSYTRD to reduce symmetric matrix to tridiagonal form.
555 *
556  CALL dsytrd( uplo, n, a, lda, work( indd ), work( inde ),
557  $ work( indtau ), work( indwk ), llwork, iinfo )
558 *
559 * If all eigenvalues are desired
560 * then call DSTERF or DSTEMR and DORMTR.
561 *
562  IF( ( alleig .OR. ( indeig .AND. il.EQ.1 .AND. iu.EQ.n ) ) .AND.
563  $ ieeeok.EQ.1 ) THEN
564  IF( .NOT.wantz ) THEN
565  CALL dcopy( n, work( indd ), 1, w, 1 )
566  CALL dcopy( n-1, work( inde ), 1, work( indee ), 1 )
567  CALL dsterf( n, w, work( indee ), info )
568  ELSE
569  CALL dcopy( n-1, work( inde ), 1, work( indee ), 1 )
570  CALL dcopy( n, work( indd ), 1, work( inddd ), 1 )
571 *
572  IF (abstol .LE. two*n*eps) THEN
573  tryrac = .true.
574  ELSE
575  tryrac = .false.
576  END IF
577  CALL dstemr( jobz, 'A', n, work( inddd ), work( indee ),
578  $ vl, vu, il, iu, m, w, z, ldz, n, isuppz,
579  $ tryrac, work( indwk ), lwork, iwork, liwork,
580  $ info )
581 *
582 *
583 *
584 * Apply orthogonal matrix used in reduction to tridiagonal
585 * form to eigenvectors returned by DSTEMR.
586 *
587  IF( wantz .AND. info.EQ.0 ) THEN
588  indwkn = inde
589  llwrkn = lwork - indwkn + 1
590  CALL dormtr( 'L', uplo, 'N', n, m, a, lda,
591  $ work( indtau ), z, ldz, work( indwkn ),
592  $ llwrkn, iinfo )
593  END IF
594  END IF
595 *
596 *
597  IF( info.EQ.0 ) THEN
598 * Everything worked. Skip DSTEBZ/DSTEIN. IWORK(:) are
599 * undefined.
600  m = n
601  GO TO 30
602  END IF
603  info = 0
604  END IF
605 *
606 * Otherwise, call DSTEBZ and, if eigenvectors are desired, DSTEIN.
607 * Also call DSTEBZ and DSTEIN if DSTEMR fails.
608 *
609  IF( wantz ) THEN
610  order = 'B'
611  ELSE
612  order = 'E'
613  END IF
614 
615  CALL dstebz( range, order, n, vll, vuu, il, iu, abstll,
616  $ work( indd ), work( inde ), m, nsplit, w,
617  $ iwork( indibl ), iwork( indisp ), work( indwk ),
618  $ iwork( indiwo ), info )
619 *
620  IF( wantz ) THEN
621  CALL dstein( n, work( indd ), work( inde ), m, w,
622  $ iwork( indibl ), iwork( indisp ), z, ldz,
623  $ work( indwk ), iwork( indiwo ), iwork( indifl ),
624  $ info )
625 *
626 * Apply orthogonal matrix used in reduction to tridiagonal
627 * form to eigenvectors returned by DSTEIN.
628 *
629  indwkn = inde
630  llwrkn = lwork - indwkn + 1
631  CALL dormtr( 'L', uplo, 'N', n, m, a, lda, work( indtau ), z,
632  $ ldz, work( indwkn ), llwrkn, iinfo )
633  END IF
634 *
635 * If matrix was scaled, then rescale eigenvalues appropriately.
636 *
637 * Jump here if DSTEMR/DSTEIN succeeded.
638  30 CONTINUE
639  IF( iscale.EQ.1 ) THEN
640  IF( info.EQ.0 ) THEN
641  imax = m
642  ELSE
643  imax = info - 1
644  END IF
645  CALL dscal( imax, one / sigma, w, 1 )
646  END IF
647 *
648 * If eigenvalues are not in order, then sort them, along with
649 * eigenvectors. Note: We do not sort the IFAIL portion of IWORK.
650 * It may not be initialized (if DSTEMR/DSTEIN succeeded), and we do
651 * not return this detailed information to the user.
652 *
653  IF( wantz ) THEN
654  DO 50 j = 1, m - 1
655  i = 0
656  tmp1 = w( j )
657  DO 40 jj = j + 1, m
658  IF( w( jj ).LT.tmp1 ) THEN
659  i = jj
660  tmp1 = w( jj )
661  END IF
662  40 CONTINUE
663 *
664  IF( i.NE.0 ) THEN
665  w( i ) = w( j )
666  w( j ) = tmp1
667  CALL dswap( n, z( 1, i ), 1, z( 1, j ), 1 )
668  END IF
669  50 CONTINUE
670  END IF
671 *
672 * Set WORK(1) to optimal workspace size.
673 *
674  work( 1 ) = lwkopt
675  iwork( 1 ) = liwmin
676 *
677  RETURN
678 *
679 * End of DSYEVR
680 *
681  END
subroutine dstein(N, D, E, M, W, IBLOCK, ISPLIT, Z, LDZ, WORK, IWORK, IFAIL, INFO)
DSTEIN
Definition: dstein.f:176
subroutine dcopy(N, DX, INCX, DY, INCY)
DCOPY
Definition: dcopy.f:84
subroutine dsytrd(UPLO, N, A, LDA, D, E, TAU, WORK, LWORK, INFO)
DSYTRD
Definition: dsytrd.f:194
subroutine dormtr(SIDE, UPLO, TRANS, M, N, A, LDA, TAU, C, LDC, WORK, LWORK, INFO)
DORMTR
Definition: dormtr.f:173
subroutine dsyevr(JOBZ, RANGE, UPLO, N, A, LDA, VL, VU, IL, IU, ABSTOL, M, W, Z, LDZ, ISUPPZ, WORK, LWORK, IWORK, LIWORK, INFO)
DSYEVR computes the eigenvalues and, optionally, the left and/or right eigenvectors for SY matrices ...
Definition: dsyevr.f:336
subroutine dsterf(N, D, E, INFO)
DSTERF
Definition: dsterf.f:88
subroutine dswap(N, DX, INCX, DY, INCY)
DSWAP
Definition: dswap.f:84
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
subroutine dscal(N, DA, DX, INCX)
DSCAL
Definition: dscal.f:81
subroutine dstemr(JOBZ, RANGE, N, D, E, VL, VU, IL, IU, M, W, Z, LDZ, NZC, ISUPPZ, TRYRAC, WORK, LWORK, IWORK, LIWORK, INFO)
DSTEMR
Definition: dstemr.f:323
subroutine dstebz(RANGE, ORDER, N, VL, VU, IL, IU, ABSTOL, D, E, M, NSPLIT, W, IBLOCK, ISPLIT, WORK, IWORK, INFO)
DSTEBZ
Definition: dstebz.f:275