LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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chbev.f
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1*> \brief <b> CHBEV 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 CHBEV + dependencies
10*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/chbev.f">
11*> [TGZ]</a>
12*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/chbev.f">
13*> [ZIP]</a>
14*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/chbev.f">
15*> [TXT]</a>
16*> \endhtmlonly
17*
18* Definition:
19* ===========
20*
21* SUBROUTINE CHBEV( JOBZ, UPLO, N, KD, AB, LDAB, W, Z, LDZ, WORK,
22* RWORK, INFO )
23*
24* .. Scalar Arguments ..
25* CHARACTER JOBZ, UPLO
26* INTEGER INFO, KD, LDAB, LDZ, N
27* ..
28* .. Array Arguments ..
29* REAL RWORK( * ), W( * )
30* COMPLEX AB( LDAB, * ), WORK( * ), Z( LDZ, * )
31* ..
32*
33*
34*> \par Purpose:
35* =============
36*>
37*> \verbatim
38*>
39*> CHBEV computes all the eigenvalues and, optionally, eigenvectors of
40*> a complex Hermitian band matrix A.
41*> \endverbatim
42*
43* Arguments:
44* ==========
45*
46*> \param[in] JOBZ
47*> \verbatim
48*> JOBZ is CHARACTER*1
49*> = 'N': Compute eigenvalues only;
50*> = 'V': Compute eigenvalues and eigenvectors.
51*> \endverbatim
52*>
53*> \param[in] UPLO
54*> \verbatim
55*> UPLO is CHARACTER*1
56*> = 'U': Upper triangle of A is stored;
57*> = 'L': Lower triangle of A is stored.
58*> \endverbatim
59*>
60*> \param[in] N
61*> \verbatim
62*> N is INTEGER
63*> The order of the matrix A. N >= 0.
64*> \endverbatim
65*>
66*> \param[in] KD
67*> \verbatim
68*> KD is INTEGER
69*> The number of superdiagonals of the matrix A if UPLO = 'U',
70*> or the number of subdiagonals if UPLO = 'L'. KD >= 0.
71*> \endverbatim
72*>
73*> \param[in,out] AB
74*> \verbatim
75*> AB is COMPLEX array, dimension (LDAB, N)
76*> On entry, the upper or lower triangle of the Hermitian band
77*> matrix A, stored in the first KD+1 rows of the array. The
78*> j-th column of A is stored in the j-th column of the array AB
79*> as follows:
80*> if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j;
81*> if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+kd).
82*>
83*> On exit, AB is overwritten by values generated during the
84*> reduction to tridiagonal form. If UPLO = 'U', the first
85*> superdiagonal and the diagonal of the tridiagonal matrix T
86*> are returned in rows KD and KD+1 of AB, and if UPLO = 'L',
87*> the diagonal and first subdiagonal of T are returned in the
88*> first two rows of AB.
89*> \endverbatim
90*>
91*> \param[in] LDAB
92*> \verbatim
93*> LDAB is INTEGER
94*> The leading dimension of the array AB. LDAB >= KD + 1.
95*> \endverbatim
96*>
97*> \param[out] W
98*> \verbatim
99*> W is REAL array, dimension (N)
100*> If INFO = 0, the eigenvalues in ascending order.
101*> \endverbatim
102*>
103*> \param[out] Z
104*> \verbatim
105*> Z is COMPLEX array, dimension (LDZ, N)
106*> If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal
107*> eigenvectors of the matrix A, with the i-th column of Z
108*> holding the eigenvector associated with W(i).
109*> If JOBZ = 'N', then Z is not referenced.
110*> \endverbatim
111*>
112*> \param[in] LDZ
113*> \verbatim
114*> LDZ is INTEGER
115*> The leading dimension of the array Z. LDZ >= 1, and if
116*> JOBZ = 'V', LDZ >= max(1,N).
117*> \endverbatim
118*>
119*> \param[out] WORK
120*> \verbatim
121*> WORK is COMPLEX array, dimension (N)
122*> \endverbatim
123*>
124*> \param[out] RWORK
125*> \verbatim
126*> RWORK is REAL array, dimension (max(1,3*N-2))
127*> \endverbatim
128*>
129*> \param[out] INFO
130*> \verbatim
131*> INFO is INTEGER
132*> = 0: successful exit.
133*> < 0: if INFO = -i, the i-th argument had an illegal value.
134*> > 0: if INFO = i, the algorithm failed to converge; i
135*> off-diagonal elements of an intermediate tridiagonal
136*> form did not converge to zero.
137*> \endverbatim
138*
139* Authors:
140* ========
141*
142*> \author Univ. of Tennessee
143*> \author Univ. of California Berkeley
144*> \author Univ. of Colorado Denver
145*> \author NAG Ltd.
146*
147*> \ingroup complexOTHEReigen
148*
149* =====================================================================
150 SUBROUTINE chbev( JOBZ, UPLO, N, KD, AB, LDAB, W, Z, LDZ, WORK,
151 $ RWORK, INFO )
152*
153* -- LAPACK driver routine --
154* -- LAPACK is a software package provided by Univ. of Tennessee, --
155* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
156*
157* .. Scalar Arguments ..
158 CHARACTER JOBZ, UPLO
159 INTEGER INFO, KD, LDAB, LDZ, N
160* ..
161* .. Array Arguments ..
162 REAL RWORK( * ), W( * )
163 COMPLEX AB( LDAB, * ), WORK( * ), Z( LDZ, * )
164* ..
165*
166* =====================================================================
167*
168* .. Parameters ..
169 REAL ZERO, ONE
170 parameter( zero = 0.0e0, one = 1.0e0 )
171* ..
172* .. Local Scalars ..
173 LOGICAL LOWER, WANTZ
174 INTEGER IINFO, IMAX, INDE, INDRWK, ISCALE
175 REAL ANRM, BIGNUM, EPS, RMAX, RMIN, SAFMIN, SIGMA,
176 $ smlnum
177* ..
178* .. External Functions ..
179 LOGICAL LSAME
180 REAL CLANHB, SLAMCH
181 EXTERNAL lsame, clanhb, slamch
182* ..
183* .. External Subroutines ..
184 EXTERNAL chbtrd, clascl, csteqr, sscal, ssterf, xerbla
185* ..
186* .. Intrinsic Functions ..
187 INTRINSIC sqrt
188* ..
189* .. Executable Statements ..
190*
191* Test the input parameters.
192*
193 wantz = lsame( jobz, 'V' )
194 lower = lsame( uplo, 'L' )
195*
196 info = 0
197 IF( .NOT.( wantz .OR. lsame( jobz, 'N' ) ) ) THEN
198 info = -1
199 ELSE IF( .NOT.( lower .OR. lsame( uplo, 'U' ) ) ) THEN
200 info = -2
201 ELSE IF( n.LT.0 ) THEN
202 info = -3
203 ELSE IF( kd.LT.0 ) THEN
204 info = -4
205 ELSE IF( ldab.LT.kd+1 ) THEN
206 info = -6
207 ELSE IF( ldz.LT.1 .OR. ( wantz .AND. ldz.LT.n ) ) THEN
208 info = -9
209 END IF
210*
211 IF( info.NE.0 ) THEN
212 CALL xerbla( 'CHBEV ', -info )
213 RETURN
214 END IF
215*
216* Quick return if possible
217*
218 IF( n.EQ.0 )
219 $ RETURN
220*
221 IF( n.EQ.1 ) THEN
222 IF( lower ) THEN
223 w( 1 ) = real( ab( 1, 1 ) )
224 ELSE
225 w( 1 ) = real( ab( kd+1, 1 ) )
226 END IF
227 IF( wantz )
228 $ z( 1, 1 ) = one
229 RETURN
230 END IF
231*
232* Get machine constants.
233*
234 safmin = slamch( 'Safe minimum' )
235 eps = slamch( 'Precision' )
236 smlnum = safmin / eps
237 bignum = one / smlnum
238 rmin = sqrt( smlnum )
239 rmax = sqrt( bignum )
240*
241* Scale matrix to allowable range, if necessary.
242*
243 anrm = clanhb( 'M', uplo, n, kd, ab, ldab, rwork )
244 iscale = 0
245 IF( anrm.GT.zero .AND. anrm.LT.rmin ) THEN
246 iscale = 1
247 sigma = rmin / anrm
248 ELSE IF( anrm.GT.rmax ) THEN
249 iscale = 1
250 sigma = rmax / anrm
251 END IF
252 IF( iscale.EQ.1 ) THEN
253 IF( lower ) THEN
254 CALL clascl( 'B', kd, kd, one, sigma, n, n, ab, ldab, info )
255 ELSE
256 CALL clascl( 'Q', kd, kd, one, sigma, n, n, ab, ldab, info )
257 END IF
258 END IF
259*
260* Call CHBTRD to reduce Hermitian band matrix to tridiagonal form.
261*
262 inde = 1
263 CALL chbtrd( jobz, uplo, n, kd, ab, ldab, w, rwork( inde ), z,
264 $ ldz, work, iinfo )
265*
266* For eigenvalues only, call SSTERF. For eigenvectors, call CSTEQR.
267*
268 IF( .NOT.wantz ) THEN
269 CALL ssterf( n, w, rwork( inde ), info )
270 ELSE
271 indrwk = inde + n
272 CALL csteqr( jobz, n, w, rwork( inde ), z, ldz,
273 $ rwork( indrwk ), info )
274 END IF
275*
276* If matrix was scaled, then rescale eigenvalues appropriately.
277*
278 IF( iscale.EQ.1 ) THEN
279 IF( info.EQ.0 ) THEN
280 imax = n
281 ELSE
282 imax = info - 1
283 END IF
284 CALL sscal( imax, one / sigma, w, 1 )
285 END IF
286*
287 RETURN
288*
289* End of CHBEV
290*
291 END
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine ssterf(N, D, E, INFO)
SSTERF
Definition: ssterf.f:86
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
subroutine chbtrd(VECT, UPLO, N, KD, AB, LDAB, D, E, Q, LDQ, WORK, INFO)
CHBTRD
Definition: chbtrd.f:163
subroutine csteqr(COMPZ, N, D, E, Z, LDZ, WORK, INFO)
CSTEQR
Definition: csteqr.f:132
subroutine chbev(JOBZ, UPLO, N, KD, AB, LDAB, W, Z, LDZ, WORK, RWORK, INFO)
CHBEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices
Definition: chbev.f:152
subroutine sscal(N, SA, SX, INCX)
SSCAL
Definition: sscal.f:79