 LAPACK  3.6.1 LAPACK: Linear Algebra PACKage
 subroutine sspevx ( character JOBZ, character RANGE, character UPLO, integer N, real, dimension( * ) AP, real VL, real VU, integer IL, integer IU, real ABSTOL, integer M, real, dimension( * ) W, real, dimension( ldz, * ) Z, integer LDZ, real, dimension( * ) WORK, integer, dimension( * ) IWORK, integer, dimension( * ) IFAIL, integer INFO )

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

Purpose:
``` SSPEVX computes selected eigenvalues and, optionally, eigenvectors
of a real symmetric matrix A in packed storage.  Eigenvalues/vectors
can be selected by specifying either a range of values or a range of
indices for the desired eigenvalues.```
Parameters
 [in] JOBZ ``` JOBZ is CHARACTER*1 = 'N': Compute eigenvalues only; = 'V': Compute eigenvalues and eigenvectors.``` [in] RANGE ``` RANGE is CHARACTER*1 = 'A': all eigenvalues will be found; = 'V': all eigenvalues in the half-open interval (VL,VU] will be found; = 'I': the IL-th through IU-th eigenvalues will be found.``` [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,out] AP ``` AP is REAL array, dimension (N*(N+1)/2) On entry, the upper or lower triangle of the symmetric matrix A, packed columnwise in a linear array. The j-th column of A is stored in the array AP as follows: if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; if UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n. On exit, AP is overwritten by values generated during the reduction to tridiagonal form. If UPLO = 'U', the diagonal and first superdiagonal of the tridiagonal matrix T overwrite the corresponding elements of A, and if UPLO = 'L', the diagonal and first subdiagonal of T overwrite the corresponding elements of A.``` [in] VL ``` VL is REAL If RANGE='V', the lower bound of the interval to be searched for eigenvalues. VL < VU. Not referenced if RANGE = 'A' or 'I'.``` [in] VU ``` VU is REAL If RANGE='V', the upper bound of the interval to be searched for eigenvalues. VL < VU. Not referenced if RANGE = 'A' or 'I'.``` [in] IL ``` IL is INTEGER If RANGE='I', the index of the smallest eigenvalue to be returned. 1 <= IL <= IU <= N, if N > 0; IL = 1 and IU = 0 if N = 0. Not referenced if RANGE = 'A' or 'V'.``` [in] IU ``` IU is INTEGER If RANGE='I', the index of the largest eigenvalue to be returned. 1 <= IL <= IU <= N, if N > 0; IL = 1 and IU = 0 if N = 0. Not referenced if RANGE = 'A' or 'V'.``` [in] ABSTOL ``` ABSTOL is REAL The absolute error tolerance for the eigenvalues. An approximate eigenvalue is accepted as converged when it is determined to lie in an interval [a,b] of width less than or equal to ABSTOL + EPS * max( |a|,|b| ) , where EPS is the machine precision. If ABSTOL is less than or equal to zero, then EPS*|T| will be used in its place, where |T| is the 1-norm of the tridiagonal matrix obtained by reducing AP to tridiagonal form. Eigenvalues will be computed most accurately when ABSTOL is set to twice the underflow threshold 2*SLAMCH('S'), not zero. If this routine returns with INFO>0, indicating that some eigenvectors did not converge, try setting ABSTOL to 2*SLAMCH('S'). See "Computing Small Singular Values of Bidiagonal Matrices with Guaranteed High Relative Accuracy," by Demmel and Kahan, LAPACK Working Note #3.``` [out] M ``` M is INTEGER The total number of eigenvalues found. 0 <= M <= N. If RANGE = 'A', M = N, and if RANGE = 'I', M = IU-IL+1.``` [out] W ``` W is REAL array, dimension (N) If INFO = 0, the selected eigenvalues in ascending order.``` [out] Z ``` Z is REAL array, dimension (LDZ, max(1,M)) If JOBZ = 'V', then if INFO = 0, the first M columns of Z contain the orthonormal eigenvectors of the matrix A corresponding to the selected eigenvalues, with the i-th column of Z holding the eigenvector associated with W(i). If an eigenvector fails to converge, then that column of Z contains the latest approximation to the eigenvector, and the index of the eigenvector is returned in IFAIL. If JOBZ = 'N', then Z is not referenced. Note: the user must ensure that at least max(1,M) columns are supplied in the array Z; if RANGE = 'V', the exact value of M is not known in advance and an upper bound must be used.``` [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 REAL array, dimension (8*N)` [out] IWORK ` IWORK is INTEGER array, dimension (5*N)` [out] IFAIL ``` IFAIL is INTEGER array, dimension (N) If JOBZ = 'V', then if INFO = 0, the first M elements of IFAIL are zero. If INFO > 0, then IFAIL contains the indices of the eigenvectors that failed to converge. If JOBZ = 'N', then IFAIL is not referenced.``` [out] INFO ``` INFO is INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value > 0: if INFO = i, then i eigenvectors failed to converge. Their indices are stored in array IFAIL.```
Date
June 2016

Definition at line 236 of file sspevx.f.

236 *
237 * -- LAPACK driver routine (version 3.6.1) --
238 * -- LAPACK is a software package provided by Univ. of Tennessee, --
239 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
240 * June 2016
241 *
242 * .. Scalar Arguments ..
243  CHARACTER jobz, range, uplo
244  INTEGER il, info, iu, ldz, m, n
245  REAL abstol, vl, vu
246 * ..
247 * .. Array Arguments ..
248  INTEGER ifail( * ), iwork( * )
249  REAL ap( * ), w( * ), work( * ), z( ldz, * )
250 * ..
251 *
252 * =====================================================================
253 *
254 * .. Parameters ..
255  REAL zero, one
256  parameter ( zero = 0.0e0, one = 1.0e0 )
257 * ..
258 * .. Local Scalars ..
259  LOGICAL alleig, indeig, test, valeig, wantz
260  CHARACTER order
261  INTEGER i, iinfo, imax, indd, inde, indee, indibl,
262  \$ indisp, indiwo, indtau, indwrk, iscale, itmp1,
263  \$ j, jj, nsplit
264  REAL abstll, anrm, bignum, eps, rmax, rmin, safmin,
265  \$ sigma, smlnum, tmp1, vll, vuu
266 * ..
267 * .. External Functions ..
268  LOGICAL lsame
269  REAL slamch, slansp
270  EXTERNAL lsame, slamch, slansp
271 * ..
272 * .. External Subroutines ..
273  EXTERNAL scopy, sopgtr, sopmtr, sscal, ssptrd, sstebz,
275 * ..
276 * .. Intrinsic Functions ..
277  INTRINSIC max, min, sqrt
278 * ..
279 * .. Executable Statements ..
280 *
281 * Test the input parameters.
282 *
283  wantz = lsame( jobz, 'V' )
284  alleig = lsame( range, 'A' )
285  valeig = lsame( range, 'V' )
286  indeig = lsame( range, 'I' )
287 *
288  info = 0
289  IF( .NOT.( wantz .OR. lsame( jobz, 'N' ) ) ) THEN
290  info = -1
291  ELSE IF( .NOT.( alleig .OR. valeig .OR. indeig ) ) THEN
292  info = -2
293  ELSE IF( .NOT.( lsame( uplo, 'L' ) .OR. lsame( uplo, 'U' ) ) )
294  \$ THEN
295  info = -3
296  ELSE IF( n.LT.0 ) THEN
297  info = -4
298  ELSE
299  IF( valeig ) THEN
300  IF( n.GT.0 .AND. vu.LE.vl )
301  \$ info = -7
302  ELSE IF( indeig ) THEN
303  IF( il.LT.1 .OR. il.GT.max( 1, n ) ) THEN
304  info = -8
305  ELSE IF( iu.LT.min( n, il ) .OR. iu.GT.n ) THEN
306  info = -9
307  END IF
308  END IF
309  END IF
310  IF( info.EQ.0 ) THEN
311  IF( ldz.LT.1 .OR. ( wantz .AND. ldz.LT.n ) )
312  \$ info = -14
313  END IF
314 *
315  IF( info.NE.0 ) THEN
316  CALL xerbla( 'SSPEVX', -info )
317  RETURN
318  END IF
319 *
320 * Quick return if possible
321 *
322  m = 0
323  IF( n.EQ.0 )
324  \$ RETURN
325 *
326  IF( n.EQ.1 ) THEN
327  IF( alleig .OR. indeig ) THEN
328  m = 1
329  w( 1 ) = ap( 1 )
330  ELSE
331  IF( vl.LT.ap( 1 ) .AND. vu.GE.ap( 1 ) ) THEN
332  m = 1
333  w( 1 ) = ap( 1 )
334  END IF
335  END IF
336  IF( wantz )
337  \$ z( 1, 1 ) = one
338  RETURN
339  END IF
340 *
341 * Get machine constants.
342 *
343  safmin = slamch( 'Safe minimum' )
344  eps = slamch( 'Precision' )
345  smlnum = safmin / eps
346  bignum = one / smlnum
347  rmin = sqrt( smlnum )
348  rmax = min( sqrt( bignum ), one / sqrt( sqrt( safmin ) ) )
349 *
350 * Scale matrix to allowable range, if necessary.
351 *
352  iscale = 0
353  abstll = abstol
354  IF ( valeig ) THEN
355  vll = vl
356  vuu = vu
357  ELSE
358  vll = zero
359  vuu = zero
360  ENDIF
361  anrm = slansp( 'M', uplo, n, ap, work )
362  IF( anrm.GT.zero .AND. anrm.LT.rmin ) THEN
363  iscale = 1
364  sigma = rmin / anrm
365  ELSE IF( anrm.GT.rmax ) THEN
366  iscale = 1
367  sigma = rmax / anrm
368  END IF
369  IF( iscale.EQ.1 ) THEN
370  CALL sscal( ( n*( n+1 ) ) / 2, sigma, ap, 1 )
371  IF( abstol.GT.0 )
372  \$ abstll = abstol*sigma
373  IF( valeig ) THEN
374  vll = vl*sigma
375  vuu = vu*sigma
376  END IF
377  END IF
378 *
379 * Call SSPTRD to reduce symmetric packed matrix to tridiagonal form.
380 *
381  indtau = 1
382  inde = indtau + n
383  indd = inde + n
384  indwrk = indd + n
385  CALL ssptrd( uplo, n, ap, work( indd ), work( inde ),
386  \$ work( indtau ), iinfo )
387 *
388 * If all eigenvalues are desired and ABSTOL is less than or equal
389 * to zero, then call SSTERF or SOPGTR and SSTEQR. If this fails
390 * for some eigenvalue, then try SSTEBZ.
391 *
392  test = .false.
393  IF (indeig) THEN
394  IF (il.EQ.1 .AND. iu.EQ.n) THEN
395  test = .true.
396  END IF
397  END IF
398  IF ((alleig .OR. test) .AND. (abstol.LE.zero)) THEN
399  CALL scopy( n, work( indd ), 1, w, 1 )
400  indee = indwrk + 2*n
401  IF( .NOT.wantz ) THEN
402  CALL scopy( n-1, work( inde ), 1, work( indee ), 1 )
403  CALL ssterf( n, w, work( indee ), info )
404  ELSE
405  CALL sopgtr( uplo, n, ap, work( indtau ), z, ldz,
406  \$ work( indwrk ), iinfo )
407  CALL scopy( n-1, work( inde ), 1, work( indee ), 1 )
408  CALL ssteqr( jobz, n, w, work( indee ), z, ldz,
409  \$ work( indwrk ), info )
410  IF( info.EQ.0 ) THEN
411  DO 10 i = 1, n
412  ifail( i ) = 0
413  10 CONTINUE
414  END IF
415  END IF
416  IF( info.EQ.0 ) THEN
417  m = n
418  GO TO 20
419  END IF
420  info = 0
421  END IF
422 *
423 * Otherwise, call SSTEBZ and, if eigenvectors are desired, SSTEIN.
424 *
425  IF( wantz ) THEN
426  order = 'B'
427  ELSE
428  order = 'E'
429  END IF
430  indibl = 1
431  indisp = indibl + n
432  indiwo = indisp + n
433  CALL sstebz( range, order, n, vll, vuu, il, iu, abstll,
434  \$ work( indd ), work( inde ), m, nsplit, w,
435  \$ iwork( indibl ), iwork( indisp ), work( indwrk ),
436  \$ iwork( indiwo ), info )
437 *
438  IF( wantz ) THEN
439  CALL sstein( n, work( indd ), work( inde ), m, w,
440  \$ iwork( indibl ), iwork( indisp ), z, ldz,
441  \$ work( indwrk ), iwork( indiwo ), ifail, info )
442 *
443 * Apply orthogonal matrix used in reduction to tridiagonal
444 * form to eigenvectors returned by SSTEIN.
445 *
446  CALL sopmtr( 'L', uplo, 'N', n, m, ap, work( indtau ), z, ldz,
447  \$ work( indwrk ), iinfo )
448  END IF
449 *
450 * If matrix was scaled, then rescale eigenvalues appropriately.
451 *
452  20 CONTINUE
453  IF( iscale.EQ.1 ) THEN
454  IF( info.EQ.0 ) THEN
455  imax = m
456  ELSE
457  imax = info - 1
458  END IF
459  CALL sscal( imax, one / sigma, w, 1 )
460  END IF
461 *
462 * If eigenvalues are not in order, then sort them, along with
463 * eigenvectors.
464 *
465  IF( wantz ) THEN
466  DO 40 j = 1, m - 1
467  i = 0
468  tmp1 = w( j )
469  DO 30 jj = j + 1, m
470  IF( w( jj ).LT.tmp1 ) THEN
471  i = jj
472  tmp1 = w( jj )
473  END IF
474  30 CONTINUE
475 *
476  IF( i.NE.0 ) THEN
477  itmp1 = iwork( indibl+i-1 )
478  w( i ) = w( j )
479  iwork( indibl+i-1 ) = iwork( indibl+j-1 )
480  w( j ) = tmp1
481  iwork( indibl+j-1 ) = itmp1
482  CALL sswap( n, z( 1, i ), 1, z( 1, j ), 1 )
483  IF( info.NE.0 ) THEN
484  itmp1 = ifail( i )
485  ifail( i ) = ifail( j )
486  ifail( j ) = itmp1
487  END IF
488  END IF
489  40 CONTINUE
490  END IF
491 *
492  RETURN
493 *
494 * End of SSPEVX
495 *
subroutine sstebz(RANGE, ORDER, N, VL, VU, IL, IU, ABSTOL, D, E, M, NSPLIT, W, IBLOCK, ISPLIT, WORK, IWORK, INFO)
SSTEBZ
Definition: sstebz.f:275
subroutine sstein(N, D, E, M, W, IBLOCK, ISPLIT, Z, LDZ, WORK, IWORK, IFAIL, INFO)
SSTEIN
Definition: sstein.f:176
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
subroutine sopgtr(UPLO, N, AP, TAU, Q, LDQ, WORK, INFO)
SOPGTR
Definition: sopgtr.f:116
subroutine ssteqr(COMPZ, N, D, E, Z, LDZ, WORK, INFO)
SSTEQR
Definition: ssteqr.f:133
subroutine sopmtr(SIDE, UPLO, TRANS, M, N, AP, TAU, C, LDC, WORK, INFO)
SOPMTR
Definition: sopmtr.f:152
real function slansp(NORM, UPLO, N, AP, WORK)
SLANSP returns the value of the 1-norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a symmetric matrix supplied in packed form.
Definition: slansp.f:116
subroutine sscal(N, SA, SX, INCX)
SSCAL
Definition: sscal.f:55
subroutine sswap(N, SX, INCX, SY, INCY)
SSWAP
Definition: sswap.f:53
real function slamch(CMACH)
SLAMCH
Definition: slamch.f:69
subroutine ssterf(N, D, E, INFO)
SSTERF
Definition: ssterf.f:88
subroutine ssptrd(UPLO, N, AP, D, E, TAU, INFO)
SSPTRD
Definition: ssptrd.f:152
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:55
subroutine scopy(N, SX, INCX, SY, INCY)
SCOPY
Definition: scopy.f:53

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