LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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chbevd.f
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1*> \brief <b> CHBEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices</b>
2*
3* =========== DOCUMENTATION ===========
4*
5* Online html documentation available at
6* http://www.netlib.org/lapack/explore-html/
7*
8*> \htmlonly
9*> Download CHBEVD + dependencies
10*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/chbevd.f">
11*> [TGZ]</a>
12*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/chbevd.f">
13*> [ZIP]</a>
14*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/chbevd.f">
15*> [TXT]</a>
16*> \endhtmlonly
17*
18* Definition:
19* ===========
20*
21* SUBROUTINE CHBEVD( JOBZ, UPLO, N, KD, AB, LDAB, W, Z, LDZ, WORK,
22* LWORK, RWORK, LRWORK, IWORK, LIWORK, INFO )
23*
24* .. Scalar Arguments ..
25* CHARACTER JOBZ, UPLO
26* INTEGER INFO, KD, LDAB, LDZ, LIWORK, LRWORK, LWORK, N
27* ..
28* .. Array Arguments ..
29* INTEGER IWORK( * )
30* REAL RWORK( * ), W( * )
31* COMPLEX AB( LDAB, * ), WORK( * ), Z( LDZ, * )
32* ..
33*
34*
35*> \par Purpose:
36* =============
37*>
38*> \verbatim
39*>
40*> CHBEVD computes all the eigenvalues and, optionally, eigenvectors of
41*> a complex Hermitian band matrix A. If eigenvectors are desired, it
42*> uses a divide and conquer algorithm.
43*>
44*> The divide and conquer algorithm makes very mild assumptions about
45*> floating point arithmetic. It will work on machines with a guard
46*> digit in add/subtract, or on those binary machines without guard
47*> digits which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or
48*> Cray-2. It could conceivably fail on hexadecimal or decimal machines
49*> without guard digits, but we know of none.
50*> \endverbatim
51*
52* Arguments:
53* ==========
54*
55*> \param[in] JOBZ
56*> \verbatim
57*> JOBZ is CHARACTER*1
58*> = 'N': Compute eigenvalues only;
59*> = 'V': Compute eigenvalues and eigenvectors.
60*> \endverbatim
61*>
62*> \param[in] UPLO
63*> \verbatim
64*> UPLO is CHARACTER*1
65*> = 'U': Upper triangle of A is stored;
66*> = 'L': Lower triangle of A is stored.
67*> \endverbatim
68*>
69*> \param[in] N
70*> \verbatim
71*> N is INTEGER
72*> The order of the matrix A. N >= 0.
73*> \endverbatim
74*>
75*> \param[in] KD
76*> \verbatim
77*> KD is INTEGER
78*> The number of superdiagonals of the matrix A if UPLO = 'U',
79*> or the number of subdiagonals if UPLO = 'L'. KD >= 0.
80*> \endverbatim
81*>
82*> \param[in,out] AB
83*> \verbatim
84*> AB is COMPLEX array, dimension (LDAB, N)
85*> On entry, the upper or lower triangle of the Hermitian band
86*> matrix A, stored in the first KD+1 rows of the array. The
87*> j-th column of A is stored in the j-th column of the array AB
88*> as follows:
89*> if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j;
90*> if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+kd).
91*>
92*> On exit, AB is overwritten by values generated during the
93*> reduction to tridiagonal form. If UPLO = 'U', the first
94*> superdiagonal and the diagonal of the tridiagonal matrix T
95*> are returned in rows KD and KD+1 of AB, and if UPLO = 'L',
96*> the diagonal and first subdiagonal of T are returned in the
97*> first two rows of AB.
98*> \endverbatim
99*>
100*> \param[in] LDAB
101*> \verbatim
102*> LDAB is INTEGER
103*> The leading dimension of the array AB. LDAB >= KD + 1.
104*> \endverbatim
105*>
106*> \param[out] W
107*> \verbatim
108*> W is REAL array, dimension (N)
109*> If INFO = 0, the eigenvalues in ascending order.
110*> \endverbatim
111*>
112*> \param[out] Z
113*> \verbatim
114*> Z is COMPLEX array, dimension (LDZ, N)
115*> If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal
116*> eigenvectors of the matrix A, with the i-th column of Z
117*> holding the eigenvector associated with W(i).
118*> If JOBZ = 'N', then Z is not referenced.
119*> \endverbatim
120*>
121*> \param[in] LDZ
122*> \verbatim
123*> LDZ is INTEGER
124*> The leading dimension of the array Z. LDZ >= 1, and if
125*> JOBZ = 'V', LDZ >= max(1,N).
126*> \endverbatim
127*>
128*> \param[out] WORK
129*> \verbatim
130*> WORK is COMPLEX array, dimension (MAX(1,LWORK))
131*> On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
132*> \endverbatim
133*>
134*> \param[in] LWORK
135*> \verbatim
136*> LWORK is INTEGER
137*> The dimension of the array WORK.
138*> If N <= 1, LWORK must be at least 1.
139*> If JOBZ = 'N' and N > 1, LWORK must be at least N.
140*> If JOBZ = 'V' and N > 1, LWORK must be at least 2*N**2.
141*>
142*> If LWORK = -1, then a workspace query is assumed; the routine
143*> only calculates the optimal sizes of the WORK, RWORK and
144*> IWORK arrays, returns these values as the first entries of
145*> the WORK, RWORK and IWORK arrays, and no error message
146*> related to LWORK or LRWORK or LIWORK is issued by XERBLA.
147*> \endverbatim
148*>
149*> \param[out] RWORK
150*> \verbatim
151*> RWORK is REAL array,
152*> dimension (LRWORK)
153*> On exit, if INFO = 0, RWORK(1) returns the optimal LRWORK.
154*> \endverbatim
155*>
156*> \param[in] LRWORK
157*> \verbatim
158*> LRWORK is INTEGER
159*> The dimension of array RWORK.
160*> If N <= 1, LRWORK must be at least 1.
161*> If JOBZ = 'N' and N > 1, LRWORK must be at least N.
162*> If JOBZ = 'V' and N > 1, LRWORK must be at least
163*> 1 + 5*N + 2*N**2.
164*>
165*> If LRWORK = -1, then a workspace query is assumed; the
166*> routine only calculates the optimal sizes of the WORK, RWORK
167*> and IWORK arrays, returns these values as the first entries
168*> of the WORK, RWORK and IWORK arrays, and no error message
169*> related to LWORK or LRWORK or LIWORK is issued by XERBLA.
170*> \endverbatim
171*>
172*> \param[out] IWORK
173*> \verbatim
174*> IWORK is INTEGER array, dimension (MAX(1,LIWORK))
175*> On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.
176*> \endverbatim
177*>
178*> \param[in] LIWORK
179*> \verbatim
180*> LIWORK is INTEGER
181*> The dimension of array IWORK.
182*> If JOBZ = 'N' or N <= 1, LIWORK must be at least 1.
183*> If JOBZ = 'V' and N > 1, LIWORK must be at least 3 + 5*N .
184*>
185*> If LIWORK = -1, then a workspace query is assumed; the
186*> routine only calculates the optimal sizes of the WORK, RWORK
187*> and IWORK arrays, returns these values as the first entries
188*> of the WORK, RWORK and IWORK arrays, and no error message
189*> related to LWORK or LRWORK or LIWORK is issued by XERBLA.
190*> \endverbatim
191*>
192*> \param[out] INFO
193*> \verbatim
194*> INFO is INTEGER
195*> = 0: successful exit.
196*> < 0: if INFO = -i, the i-th argument had an illegal value.
197*> > 0: if INFO = i, the algorithm failed to converge; i
198*> off-diagonal elements of an intermediate tridiagonal
199*> form did not converge to zero.
200*> \endverbatim
201*
202* Authors:
203* ========
204*
205*> \author Univ. of Tennessee
206*> \author Univ. of California Berkeley
207*> \author Univ. of Colorado Denver
208*> \author NAG Ltd.
209*
210*> \ingroup complexOTHEReigen
211*
212* =====================================================================
213 SUBROUTINE chbevd( JOBZ, UPLO, N, KD, AB, LDAB, W, Z, LDZ, WORK,
214 $ LWORK, RWORK, LRWORK, IWORK, LIWORK, INFO )
215*
216* -- LAPACK driver routine --
217* -- LAPACK is a software package provided by Univ. of Tennessee, --
218* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
219*
220* .. Scalar Arguments ..
221 CHARACTER JOBZ, UPLO
222 INTEGER INFO, KD, LDAB, LDZ, LIWORK, LRWORK, LWORK, N
223* ..
224* .. Array Arguments ..
225 INTEGER IWORK( * )
226 REAL RWORK( * ), W( * )
227 COMPLEX AB( LDAB, * ), WORK( * ), Z( LDZ, * )
228* ..
229*
230* =====================================================================
231*
232* .. Parameters ..
233 REAL ZERO, ONE
234 parameter( zero = 0.0e0, one = 1.0e0 )
235 COMPLEX CZERO, CONE
236 parameter( czero = ( 0.0e0, 0.0e0 ),
237 $ cone = ( 1.0e0, 0.0e0 ) )
238* ..
239* .. Local Scalars ..
240 LOGICAL LOWER, LQUERY, WANTZ
241 INTEGER IINFO, IMAX, INDE, INDWK2, INDWRK, ISCALE,
242 $ liwmin, llrwk, llwk2, lrwmin, lwmin
243 REAL ANRM, BIGNUM, EPS, RMAX, RMIN, SAFMIN, SIGMA,
244 $ smlnum
245* ..
246* .. External Functions ..
247 LOGICAL LSAME
248 REAL CLANHB, SLAMCH
249 EXTERNAL lsame, clanhb, slamch
250* ..
251* .. External Subroutines ..
252 EXTERNAL cgemm, chbtrd, clacpy, clascl, cstedc, sscal,
253 $ ssterf, xerbla
254* ..
255* .. Intrinsic Functions ..
256 INTRINSIC sqrt
257* ..
258* .. Executable Statements ..
259*
260* Test the input parameters.
261*
262 wantz = lsame( jobz, 'V' )
263 lower = lsame( uplo, 'L' )
264 lquery = ( lwork.EQ.-1 .OR. liwork.EQ.-1 .OR. lrwork.EQ.-1 )
265*
266 info = 0
267 IF( n.LE.1 ) THEN
268 lwmin = 1
269 lrwmin = 1
270 liwmin = 1
271 ELSE
272 IF( wantz ) THEN
273 lwmin = 2*n**2
274 lrwmin = 1 + 5*n + 2*n**2
275 liwmin = 3 + 5*n
276 ELSE
277 lwmin = n
278 lrwmin = n
279 liwmin = 1
280 END IF
281 END IF
282 IF( .NOT.( wantz .OR. lsame( jobz, 'N' ) ) ) THEN
283 info = -1
284 ELSE IF( .NOT.( lower .OR. lsame( uplo, 'U' ) ) ) THEN
285 info = -2
286 ELSE IF( n.LT.0 ) THEN
287 info = -3
288 ELSE IF( kd.LT.0 ) THEN
289 info = -4
290 ELSE IF( ldab.LT.kd+1 ) THEN
291 info = -6
292 ELSE IF( ldz.LT.1 .OR. ( wantz .AND. ldz.LT.n ) ) THEN
293 info = -9
294 END IF
295*
296 IF( info.EQ.0 ) THEN
297 work( 1 ) = lwmin
298 rwork( 1 ) = lrwmin
299 iwork( 1 ) = liwmin
300*
301 IF( lwork.LT.lwmin .AND. .NOT.lquery ) THEN
302 info = -11
303 ELSE IF( lrwork.LT.lrwmin .AND. .NOT.lquery ) THEN
304 info = -13
305 ELSE IF( liwork.LT.liwmin .AND. .NOT.lquery ) THEN
306 info = -15
307 END IF
308 END IF
309*
310 IF( info.NE.0 ) THEN
311 CALL xerbla( 'CHBEVD', -info )
312 RETURN
313 ELSE IF( lquery ) THEN
314 RETURN
315 END IF
316*
317* Quick return if possible
318*
319 IF( n.EQ.0 )
320 $ RETURN
321*
322 IF( n.EQ.1 ) THEN
323 w( 1 ) = real( ab( 1, 1 ) )
324 IF( wantz )
325 $ z( 1, 1 ) = cone
326 RETURN
327 END IF
328*
329* Get machine constants.
330*
331 safmin = slamch( 'Safe minimum' )
332 eps = slamch( 'Precision' )
333 smlnum = safmin / eps
334 bignum = one / smlnum
335 rmin = sqrt( smlnum )
336 rmax = sqrt( bignum )
337*
338* Scale matrix to allowable range, if necessary.
339*
340 anrm = clanhb( 'M', uplo, n, kd, ab, ldab, rwork )
341 iscale = 0
342 IF( anrm.GT.zero .AND. anrm.LT.rmin ) THEN
343 iscale = 1
344 sigma = rmin / anrm
345 ELSE IF( anrm.GT.rmax ) THEN
346 iscale = 1
347 sigma = rmax / anrm
348 END IF
349 IF( iscale.EQ.1 ) THEN
350 IF( lower ) THEN
351 CALL clascl( 'B', kd, kd, one, sigma, n, n, ab, ldab, info )
352 ELSE
353 CALL clascl( 'Q', kd, kd, one, sigma, n, n, ab, ldab, info )
354 END IF
355 END IF
356*
357* Call CHBTRD to reduce Hermitian band matrix to tridiagonal form.
358*
359 inde = 1
360 indwrk = inde + n
361 indwk2 = 1 + n*n
362 llwk2 = lwork - indwk2 + 1
363 llrwk = lrwork - indwrk + 1
364 CALL chbtrd( jobz, uplo, n, kd, ab, ldab, w, rwork( inde ), z,
365 $ ldz, work, iinfo )
366*
367* For eigenvalues only, call SSTERF. For eigenvectors, call CSTEDC.
368*
369 IF( .NOT.wantz ) THEN
370 CALL ssterf( n, w, rwork( inde ), info )
371 ELSE
372 CALL cstedc( 'I', n, w, rwork( inde ), work, n, work( indwk2 ),
373 $ llwk2, rwork( indwrk ), llrwk, iwork, liwork,
374 $ info )
375 CALL cgemm( 'N', 'N', n, n, n, cone, z, ldz, work, n, czero,
376 $ work( indwk2 ), n )
377 CALL clacpy( 'A', n, n, work( indwk2 ), n, z, ldz )
378 END IF
379*
380* If matrix was scaled, then rescale eigenvalues appropriately.
381*
382 IF( iscale.EQ.1 ) THEN
383 IF( info.EQ.0 ) THEN
384 imax = n
385 ELSE
386 imax = info - 1
387 END IF
388 CALL sscal( imax, one / sigma, w, 1 )
389 END IF
390*
391 work( 1 ) = lwmin
392 rwork( 1 ) = lrwmin
393 iwork( 1 ) = liwmin
394 RETURN
395*
396* End of CHBEVD
397*
398 END
xerbla
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
ssterf
subroutine ssterf(N, D, E, INFO)
SSTERF
Definition: ssterf.f:86
cgemm
subroutine cgemm(TRANSA, TRANSB, M, N, K, ALPHA, A, LDA, B, LDB, BETA, C, LDC)
CGEMM
Definition: cgemm.f:187
clascl
subroutine clascl(TYPE, KL, KU, CFROM, CTO, M, N, A, LDA, INFO)
CLASCL multiplies a general rectangular matrix by a real scalar defined as cto/cfrom.
Definition: clascl.f:143
clacpy
subroutine clacpy(UPLO, M, N, A, LDA, B, LDB)
CLACPY copies all or part of one two-dimensional array to another.
Definition: clacpy.f:103
chbtrd
subroutine chbtrd(VECT, UPLO, N, KD, AB, LDAB, D, E, Q, LDQ, WORK, INFO)
CHBTRD
Definition: chbtrd.f:163
cstedc
subroutine cstedc(COMPZ, N, D, E, Z, LDZ, WORK, LWORK, RWORK, LRWORK, IWORK, LIWORK, INFO)
CSTEDC
Definition: cstedc.f:212
chbevd
subroutine chbevd(JOBZ, UPLO, N, KD, AB, LDAB, W, Z, LDZ, WORK, LWORK, RWORK, LRWORK, IWORK, LIWORK, INFO)
CHBEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrice...
Definition: chbevd.f:215
sscal
subroutine sscal(N, SA, SX, INCX)
SSCAL
Definition: sscal.f:79