LAPACK 3.12.1
LAPACK: Linear Algebra PACKage
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◆ chbev_2stage()

subroutine chbev_2stage ( character jobz,
character uplo,
integer n,
integer kd,
complex, dimension( ldab, * ) ab,
integer ldab,
real, dimension( * ) w,
complex, dimension( ldz, * ) z,
integer ldz,
complex, dimension( * ) work,
integer lwork,
real, dimension( * ) rwork,
integer info )

CHBEV_2STAGE computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices

Download CHBEV_2STAGE + dependencies [TGZ] [ZIP] [TXT]

Purpose:
!>
!> CHBEV_2STAGE computes all the eigenvalues and, optionally, eigenvectors of
!> a complex Hermitian band matrix A using the 2stage technique for
!> the reduction to tridiagonal.
!>
Parameters
[in]JOBZ
!>          JOBZ is CHARACTER*1
!>          = 'N':  Compute eigenvalues only;
!>          = 'V':  Compute eigenvalues and eigenvectors.
!>                  Not available in this release.
!>
[in]UPLO
!>          UPLO is CHARACTER*1
!>          = 'U':  Upper triangle of A is stored;
!>          = 'L':  Lower triangle of A is stored.
!>
[in]N
!>          N is INTEGER
!>          The order of the matrix A.  N >= 0.
!>
[in]KD
!>          KD is INTEGER
!>          The number of superdiagonals of the matrix A if UPLO = 'U',
!>          or the number of subdiagonals if UPLO = 'L'.  KD >= 0.
!>
[in,out]AB
!>          AB is COMPLEX array, dimension (LDAB, N)
!>          On entry, the upper or lower triangle of the Hermitian band
!>          matrix A, stored in the first KD+1 rows of the array.  The
!>          j-th column of A is stored in the j-th column of the array AB
!>          as follows:
!>          if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j;
!>          if UPLO = 'L', AB(1+i-j,j)    = A(i,j) for j<=i<=min(n,j+kd).
!>
!>          On exit, AB is overwritten by values generated during the
!>          reduction to tridiagonal form.  If UPLO = 'U', the first
!>          superdiagonal and the diagonal of the tridiagonal matrix T
!>          are returned in rows KD and KD+1 of AB, and if UPLO = 'L',
!>          the diagonal and first subdiagonal of T are returned in the
!>          first two rows of AB.
!>
[in]LDAB
!>          LDAB is INTEGER
!>          The leading dimension of the array AB.  LDAB >= KD + 1.
!>
[out]W
!>          W is REAL array, dimension (N)
!>          If INFO = 0, the eigenvalues in ascending order.
!>
[out]Z
!>          Z is COMPLEX array, dimension (LDZ, N)
!>          If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal
!>          eigenvectors of the matrix A, with the i-th column of Z
!>          holding the eigenvector associated with W(i).
!>          If JOBZ = 'N', then Z is not referenced.
!>
[in]LDZ
!>          LDZ is INTEGER
!>          The leading dimension of the array Z.  LDZ >= 1, and if
!>          JOBZ = 'V', LDZ >= max(1,N).
!>
[out]WORK
!>          WORK is COMPLEX array, dimension LWORK
!>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
!>
[in]LWORK
!>          LWORK is INTEGER
!>          The length of the array WORK. LWORK >= 1, when N <= 1;
!>          otherwise
!>          If JOBZ = 'N' and N > 1, LWORK must be queried.
!>                                   LWORK = MAX(1, dimension) where
!>                                   dimension = (2KD+1)*N + KD*NTHREADS
!>                                   where KD is the size of the band.
!>                                   NTHREADS is the number of threads used when
!>                                   openMP compilation is enabled, otherwise =1.
!>          If JOBZ = 'V' and N > 1, LWORK must be queried. Not yet available.
!>
!>          If LWORK = -1, then a workspace query is assumed; the routine
!>          only calculates the optimal sizes of the WORK, RWORK and
!>          IWORK arrays, returns these values as the first entries of
!>          the WORK, RWORK and IWORK arrays, and no error message
!>          related to LWORK or LRWORK or LIWORK is issued by XERBLA.
!>
[out]RWORK
!>          RWORK is REAL array, dimension (max(1,3*N-2))
!>
[out]INFO
!>          INFO is INTEGER
!>          = 0:  successful exit.
!>          < 0:  if INFO = -i, the i-th argument had an illegal value.
!>          > 0:  if INFO = i, the algorithm failed to converge; i
!>                off-diagonal elements of an intermediate tridiagonal
!>                form did not converge to zero.
!>
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Further Details:
!>
!>  All details about the 2stage techniques are available in:
!>
!>  Azzam Haidar, Hatem Ltaief, and Jack Dongarra.
!>  Parallel reduction to condensed forms for symmetric eigenvalue problems
!>  using aggregated fine-grained and memory-aware kernels. In Proceedings
!>  of 2011 International Conference for High Performance Computing,
!>  Networking, Storage and Analysis (SC '11), New York, NY, USA,
!>  Article 8 , 11 pages.
!>  http://doi.acm.org/10.1145/2063384.2063394
!>
!>  A. Haidar, J. Kurzak, P. Luszczek, 2013.
!>  An improved parallel singular value algorithm and its implementation
!>  for multicore hardware, In Proceedings of 2013 International Conference
!>  for High Performance Computing, Networking, Storage and Analysis (SC '13).
!>  Denver, Colorado, USA, 2013.
!>  Article 90, 12 pages.
!>  http://doi.acm.org/10.1145/2503210.2503292
!>
!>  A. Haidar, R. Solca, S. Tomov, T. Schulthess and J. Dongarra.
!>  A novel hybrid CPU-GPU generalized eigensolver for electronic structure
!>  calculations based on fine-grained memory aware tasks.
!>  International Journal of High Performance Computing Applications.
!>  Volume 28 Issue 2, Pages 196-209, May 2014.
!>  http://hpc.sagepub.com/content/28/2/196
!>
!>

Definition at line 207 of file chbev_2stage.f.

210*
211 IMPLICIT NONE
212*
213* -- LAPACK driver routine --
214* -- LAPACK is a software package provided by Univ. of Tennessee, --
215* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
216*
217* .. Scalar Arguments ..
218 CHARACTER JOBZ, UPLO
219 INTEGER INFO, KD, LDAB, LDZ, N, LWORK
220* ..
221* .. Array Arguments ..
222 REAL RWORK( * ), W( * )
223 COMPLEX AB( LDAB, * ), WORK( * ), Z( LDZ, * )
224* ..
225*
226* =====================================================================
227*
228* .. Parameters ..
229 REAL ZERO, ONE
230 parameter( zero = 0.0e0, one = 1.0e0 )
231* ..
232* .. Local Scalars ..
233 LOGICAL LOWER, WANTZ, LQUERY
234 INTEGER IINFO, IMAX, INDE, INDWRK, INDRWK, ISCALE,
235 $ LLWORK, LWMIN, LHTRD, LWTRD, IB, INDHOUS
236 REAL ANRM, BIGNUM, EPS, RMAX, RMIN, SAFMIN, SIGMA,
237 $ SMLNUM
238* ..
239* .. External Functions ..
240 LOGICAL LSAME
241 INTEGER ILAENV2STAGE
242 REAL SLAMCH, CLANHB, SROUNDUP_LWORK
243 EXTERNAL lsame, slamch, clanhb, ilaenv2stage,
244 $ sroundup_lwork
245* ..
246* .. External Subroutines ..
247 EXTERNAL sscal, ssterf, xerbla, clascl,
248 $ csteqr,
249 $ chetrd_2stage, chetrd_hb2st
250* ..
251* .. Intrinsic Functions ..
252 INTRINSIC real, sqrt
253* ..
254* .. Executable Statements ..
255*
256* Test the input parameters.
257*
258 wantz = lsame( jobz, 'V' )
259 lower = lsame( uplo, 'L' )
260 lquery = ( lwork.EQ.-1 )
261*
262 info = 0
263 IF( .NOT.( lsame( jobz, 'N' ) ) ) THEN
264 info = -1
265 ELSE IF( .NOT.( lower .OR. lsame( uplo, 'U' ) ) ) THEN
266 info = -2
267 ELSE IF( n.LT.0 ) THEN
268 info = -3
269 ELSE IF( kd.LT.0 ) THEN
270 info = -4
271 ELSE IF( ldab.LT.kd+1 ) THEN
272 info = -6
273 ELSE IF( ldz.LT.1 .OR. ( wantz .AND. ldz.LT.n ) ) THEN
274 info = -9
275 END IF
276*
277 IF( info.EQ.0 ) THEN
278 IF( n.LE.1 ) THEN
279 lwmin = 1
280 work( 1 ) = sroundup_lwork(lwmin)
281 ELSE
282 ib = ilaenv2stage( 2, 'CHETRD_HB2ST', jobz,
283 $ n, kd, -1, -1 )
284 lhtrd = ilaenv2stage( 3, 'CHETRD_HB2ST', jobz,
285 $ n, kd, ib, -1 )
286 lwtrd = ilaenv2stage( 4, 'CHETRD_HB2ST', jobz,
287 $ n, kd, ib, -1 )
288 lwmin = lhtrd + lwtrd
289 work( 1 ) = sroundup_lwork(lwmin)
290 ENDIF
291*
292 IF( lwork.LT.lwmin .AND. .NOT.lquery )
293 $ info = -11
294 END IF
295*
296 IF( info.NE.0 ) THEN
297 CALL xerbla( 'CHBEV_2STAGE ', -info )
298 RETURN
299 ELSE IF( lquery ) THEN
300 RETURN
301 END IF
302*
303* Quick return if possible
304*
305 IF( n.EQ.0 )
306 $ RETURN
307*
308 IF( n.EQ.1 ) THEN
309 IF( lower ) THEN
310 w( 1 ) = real( ab( 1, 1 ) )
311 ELSE
312 w( 1 ) = real( ab( kd+1, 1 ) )
313 END IF
314 IF( wantz )
315 $ z( 1, 1 ) = one
316 RETURN
317 END IF
318*
319* Get machine constants.
320*
321 safmin = slamch( 'Safe minimum' )
322 eps = slamch( 'Precision' )
323 smlnum = safmin / eps
324 bignum = one / smlnum
325 rmin = sqrt( smlnum )
326 rmax = sqrt( bignum )
327*
328* Scale matrix to allowable range, if necessary.
329*
330 anrm = clanhb( 'M', uplo, n, kd, ab, ldab, rwork )
331 iscale = 0
332 IF( anrm.GT.zero .AND. anrm.LT.rmin ) THEN
333 iscale = 1
334 sigma = rmin / anrm
335 ELSE IF( anrm.GT.rmax ) THEN
336 iscale = 1
337 sigma = rmax / anrm
338 END IF
339 IF( iscale.EQ.1 ) THEN
340 IF( lower ) THEN
341 CALL clascl( 'B', kd, kd, one, sigma, n, n, ab, ldab,
342 $ info )
343 ELSE
344 CALL clascl( 'Q', kd, kd, one, sigma, n, n, ab, ldab,
345 $ info )
346 END IF
347 END IF
348*
349* Call CHBTRD_HB2ST to reduce Hermitian band matrix to tridiagonal form.
350*
351 inde = 1
352 indhous = 1
353 indwrk = indhous + lhtrd
354 llwork = lwork - indwrk + 1
355*
356 CALL chetrd_hb2st( "N", jobz, uplo, n, kd, ab, ldab, w,
357 $ rwork( inde ), work( indhous ), lhtrd,
358 $ work( indwrk ), llwork, iinfo )
359*
360* For eigenvalues only, call SSTERF. For eigenvectors, call CSTEQR.
361*
362 IF( .NOT.wantz ) THEN
363 CALL ssterf( n, w, rwork( inde ), info )
364 ELSE
365 indrwk = inde + n
366 CALL csteqr( jobz, n, w, rwork( inde ), z, ldz,
367 $ rwork( indrwk ), info )
368 END IF
369*
370* If matrix was scaled, then rescale eigenvalues appropriately.
371*
372 IF( iscale.EQ.1 ) THEN
373 IF( info.EQ.0 ) THEN
374 imax = n
375 ELSE
376 imax = info - 1
377 END IF
378 CALL sscal( imax, one / sigma, w, 1 )
379 END IF
380*
381* Set WORK(1) to optimal workspace size.
382*
383 work( 1 ) = sroundup_lwork(lwmin)
384*
385 RETURN
386*
387* End of CHBEV_2STAGE
388*
xerbla
subroutine xerbla(srname, info)
Definition cblat2.f:3285
chetrd_2stage
subroutine chetrd_2stage(vect, uplo, n, a, lda, d, e, tau, hous2, lhous2, work, lwork, info)
CHETRD_2STAGE
Definition chetrd_2stage.f:227
chetrd_hb2st
subroutine chetrd_hb2st(stage1, vect, uplo, n, kd, ab, ldab, d, e, hous, lhous, work, lwork, info)
CHETRD_HB2ST reduces a complex Hermitian band matrix A to real symmetric tridiagonal form T
Definition chetrd_hb2st.F:233
ilaenv2stage
integer function ilaenv2stage(ispec, name, opts, n1, n2, n3, n4)
ILAENV2STAGE
Definition ilaenv2stage.f:148
slamch
real function slamch(cmach)
SLAMCH
Definition slamch.f:68
clanhb
real function clanhb(norm, uplo, n, k, ab, ldab, work)
CLANHB returns the value of the 1-norm, or the Frobenius norm, or the infinity norm,...
Definition clanhb.f:130
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:142
lsame
logical function lsame(ca, cb)
LSAME
Definition lsame.f:48
sroundup_lwork
real function sroundup_lwork(lwork)
SROUNDUP_LWORK
Definition sroundup_lwork.f:59
sscal
subroutine sscal(n, sa, sx, incx)
SSCAL
Definition sscal.f:79
csteqr
subroutine csteqr(compz, n, d, e, z, ldz, work, info)
CSTEQR
Definition csteqr.f:130
ssterf
subroutine ssterf(n, d, e, info)
SSTERF
Definition ssterf.f:84
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