203 $ WORK, LWORK, INFO )
213 INTEGER INFO, KD, LDAB, LDZ, N, LWORK
216 REAL AB( LDAB, * ), W( * ), WORK( * ), Z( LDZ, * )
223 parameter( zero = 0.0e0, one = 1.0e0 )
226 LOGICAL LOWER, WANTZ, LQUERY
227 INTEGER IINFO, IMAX, INDE, INDWRK, ISCALE,
228 $ llwork, lwmin, lhtrd, lwtrd, ib, indhous
229 REAL ANRM, BIGNUM, EPS, RMAX, RMIN, SAFMIN, SIGMA,
235 REAL SLAMCH, SLANSB, SROUNDUP_LWORK
236 EXTERNAL lsame, slamch, slansb, ilaenv2stage,
250 wantz = lsame( jobz,
'V' )
251 lower = lsame( uplo,
'L' )
252 lquery = ( lwork.EQ.-1 )
255 IF( .NOT.( lsame( jobz,
'N' ) ) )
THEN
257 ELSE IF( .NOT.( lower .OR. lsame( uplo,
'U' ) ) )
THEN
259 ELSE IF( n.LT.0 )
THEN
261 ELSE IF( kd.LT.0 )
THEN
263 ELSE IF( ldab.LT.kd+1 )
THEN
265 ELSE IF( ldz.LT.1 .OR. ( wantz .AND. ldz.LT.n ) )
THEN
272 work( 1 ) = sroundup_lwork(lwmin)
274 ib = ilaenv2stage( 2,
'SSYTRD_SB2ST', jobz,
276 lhtrd = ilaenv2stage( 3,
'SSYTRD_SB2ST', jobz,
278 lwtrd = ilaenv2stage( 4,
'SSYTRD_SB2ST', jobz,
280 lwmin = n + lhtrd + lwtrd
281 work( 1 ) = sroundup_lwork(lwmin)
284 IF( lwork.LT.lwmin .AND. .NOT.lquery )
289 CALL xerbla(
'SSBEV_2STAGE ', -info )
291 ELSE IF( lquery )
THEN
304 w( 1 ) = ab( kd+1, 1 )
313 safmin = slamch(
'Safe minimum' )
314 eps = slamch(
'Precision' )
315 smlnum = safmin / eps
316 bignum = one / smlnum
317 rmin = sqrt( smlnum )
318 rmax = sqrt( bignum )
322 anrm = slansb(
'M', uplo, n, kd, ab, ldab, work )
324 IF( anrm.GT.zero .AND. anrm.LT.rmin )
THEN
327 ELSE IF( anrm.GT.rmax )
THEN
331 IF( iscale.EQ.1 )
THEN
333 CALL slascl(
'B', kd, kd, one, sigma, n, n, ab, ldab, info )
335 CALL slascl(
'Q', kd, kd, one, sigma, n, n, ab, ldab, info )
343 indwrk = indhous + lhtrd
344 llwork = lwork - indwrk + 1
347 $ work( inde ), work( indhous ), lhtrd,
348 $ work( indwrk ), llwork, iinfo )
352 IF( .NOT.wantz )
THEN
353 CALL ssterf( n, w, work( inde ), info )
355 CALL ssteqr( jobz, n, w, work( inde ), z, ldz, work( indwrk ),
361 IF( iscale.EQ.1 )
THEN
367 CALL sscal( imax, one / sigma, w, 1 )
372 work( 1 ) = sroundup_lwork(lwmin)
subroutine xerbla(srname, info)
subroutine ssbev_2stage(jobz, uplo, n, kd, ab, ldab, w, z, ldz, work, lwork, info)
SSBEV_2STAGE computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER m...
subroutine ssytrd_sb2st(stage1, vect, uplo, n, kd, ab, ldab, d, e, hous, lhous, work, lwork, info)
SSYTRD_SB2ST reduces a real symmetric band matrix A to real symmetric tridiagonal form T
subroutine slascl(type, kl, ku, cfrom, cto, m, n, a, lda, info)
SLASCL multiplies a general rectangular matrix by a real scalar defined as cto/cfrom.
subroutine sscal(n, sa, sx, incx)
SSCAL
subroutine ssteqr(compz, n, d, e, z, ldz, work, info)
SSTEQR
subroutine ssterf(n, d, e, info)
SSTERF