 LAPACK  3.10.0 LAPACK: Linear Algebra PACKage

## ◆ chbgvx()

 subroutine chbgvx ( character JOBZ, character RANGE, character UPLO, integer N, integer KA, integer KB, complex, dimension( ldab, * ) AB, integer LDAB, complex, dimension( ldbb, * ) BB, integer LDBB, complex, dimension( ldq, * ) Q, integer LDQ, real VL, real VU, integer IL, integer IU, real ABSTOL, integer M, real, dimension( * ) W, complex, dimension( ldz, * ) Z, integer LDZ, complex, dimension( * ) WORK, real, dimension( * ) RWORK, integer, dimension( * ) IWORK, integer, dimension( * ) IFAIL, integer INFO )

CHBGVX

Purpose:
``` CHBGVX computes all the eigenvalues, and optionally, the eigenvectors
of a complex generalized Hermitian-definite banded eigenproblem, of
the form A*x=(lambda)*B*x. Here A and B are assumed to be Hermitian
and banded, and B is also positive definite.  Eigenvalues and
eigenvectors can be selected by specifying either all eigenvalues,
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 triangles of A and B are stored; = 'L': Lower triangles of A and B are stored.``` [in] N ``` N is INTEGER The order of the matrices A and B. N >= 0.``` [in] KA ``` KA is INTEGER The number of superdiagonals of the matrix A if UPLO = 'U', or the number of subdiagonals if UPLO = 'L'. KA >= 0.``` [in] KB ``` KB is INTEGER The number of superdiagonals of the matrix B if UPLO = 'U', or the number of subdiagonals if UPLO = 'L'. KB >= 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 ka+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(ka+1+i-j,j) = A(i,j) for max(1,j-ka)<=i<=j; if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+ka). On exit, the contents of AB are destroyed.``` [in] LDAB ``` LDAB is INTEGER The leading dimension of the array AB. LDAB >= KA+1.``` [in,out] BB ``` BB is COMPLEX array, dimension (LDBB, N) On entry, the upper or lower triangle of the Hermitian band matrix B, stored in the first kb+1 rows of the array. The j-th column of B is stored in the j-th column of the array BB as follows: if UPLO = 'U', BB(kb+1+i-j,j) = B(i,j) for max(1,j-kb)<=i<=j; if UPLO = 'L', BB(1+i-j,j) = B(i,j) for j<=i<=min(n,j+kb). On exit, the factor S from the split Cholesky factorization B = S**H*S, as returned by CPBSTF.``` [in] LDBB ``` LDBB is INTEGER The leading dimension of the array BB. LDBB >= KB+1.``` [out] Q ``` Q is COMPLEX array, dimension (LDQ, N) If JOBZ = 'V', the n-by-n matrix used in the reduction of A*x = (lambda)*B*x to standard form, i.e. C*x = (lambda)*x, and consequently C to tridiagonal form. If JOBZ = 'N', the array Q is not referenced.``` [in] LDQ ``` LDQ is INTEGER The leading dimension of the array Q. If JOBZ = 'N', LDQ >= 1. If JOBZ = 'V', LDQ >= max(1,N).``` [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').``` [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 eigenvalues in ascending order.``` [out] Z ``` Z is COMPLEX array, dimension (LDZ, N) If JOBZ = 'V', then if INFO = 0, Z contains the matrix Z of eigenvectors, with the i-th column of Z holding the eigenvector associated with W(i). The eigenvectors are normalized so that Z**H*B*Z = 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 >= N.``` [out] WORK ` WORK is COMPLEX array, dimension (N)` [out] RWORK ` RWORK is REAL array, dimension (7*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, and i is: <= N: then i eigenvectors failed to converge. Their indices are stored in array IFAIL. > N: if INFO = N + i, for 1 <= i <= N, then CPBSTF returned INFO = i: B is not positive definite. The factorization of B could not be completed and no eigenvalues or eigenvectors were computed.```
Contributors:
Mark Fahey, Department of Mathematics, Univ. of Kentucky, USA

Definition at line 297 of file chbgvx.f.

300 *
301 * -- LAPACK driver routine --
302 * -- LAPACK is a software package provided by Univ. of Tennessee, --
303 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
304 *
305 * .. Scalar Arguments ..
306  CHARACTER JOBZ, RANGE, UPLO
307  INTEGER IL, INFO, IU, KA, KB, LDAB, LDBB, LDQ, LDZ, M,
308  \$ N
309  REAL ABSTOL, VL, VU
310 * ..
311 * .. Array Arguments ..
312  INTEGER IFAIL( * ), IWORK( * )
313  REAL RWORK( * ), W( * )
314  COMPLEX AB( LDAB, * ), BB( LDBB, * ), Q( LDQ, * ),
315  \$ WORK( * ), Z( LDZ, * )
316 * ..
317 *
318 * =====================================================================
319 *
320 * .. Parameters ..
321  REAL ZERO
322  parameter( zero = 0.0e+0 )
323  COMPLEX CZERO, CONE
324  parameter( czero = ( 0.0e+0, 0.0e+0 ),
325  \$ cone = ( 1.0e+0, 0.0e+0 ) )
326 * ..
327 * .. Local Scalars ..
328  LOGICAL ALLEIG, INDEIG, TEST, UPPER, VALEIG, WANTZ
329  CHARACTER ORDER, VECT
330  INTEGER I, IINFO, INDD, INDE, INDEE, INDIBL, INDISP,
331  \$ INDIWK, INDRWK, INDWRK, ITMP1, J, JJ, NSPLIT
332  REAL TMP1
333 * ..
334 * .. External Functions ..
335  LOGICAL LSAME
336  EXTERNAL lsame
337 * ..
338 * .. External Subroutines ..
339  EXTERNAL ccopy, cgemv, chbgst, chbtrd, clacpy, cpbstf,
341  \$ xerbla
342 * ..
343 * .. Intrinsic Functions ..
344  INTRINSIC min
345 * ..
346 * .. Executable Statements ..
347 *
348 * Test the input parameters.
349 *
350  wantz = lsame( jobz, 'V' )
351  upper = lsame( uplo, 'U' )
352  alleig = lsame( range, 'A' )
353  valeig = lsame( range, 'V' )
354  indeig = lsame( range, 'I' )
355 *
356  info = 0
357  IF( .NOT.( wantz .OR. lsame( jobz, 'N' ) ) ) THEN
358  info = -1
359  ELSE IF( .NOT.( alleig .OR. valeig .OR. indeig ) ) THEN
360  info = -2
361  ELSE IF( .NOT.( upper .OR. lsame( uplo, 'L' ) ) ) THEN
362  info = -3
363  ELSE IF( n.LT.0 ) THEN
364  info = -4
365  ELSE IF( ka.LT.0 ) THEN
366  info = -5
367  ELSE IF( kb.LT.0 .OR. kb.GT.ka ) THEN
368  info = -6
369  ELSE IF( ldab.LT.ka+1 ) THEN
370  info = -8
371  ELSE IF( ldbb.LT.kb+1 ) THEN
372  info = -10
373  ELSE IF( ldq.LT.1 .OR. ( wantz .AND. ldq.LT.n ) ) THEN
374  info = -12
375  ELSE
376  IF( valeig ) THEN
377  IF( n.GT.0 .AND. vu.LE.vl )
378  \$ info = -14
379  ELSE IF( indeig ) THEN
380  IF( il.LT.1 .OR. il.GT.max( 1, n ) ) THEN
381  info = -15
382  ELSE IF ( iu.LT.min( n, il ) .OR. iu.GT.n ) THEN
383  info = -16
384  END IF
385  END IF
386  END IF
387  IF( info.EQ.0) THEN
388  IF( ldz.LT.1 .OR. ( wantz .AND. ldz.LT.n ) ) THEN
389  info = -21
390  END IF
391  END IF
392 *
393  IF( info.NE.0 ) THEN
394  CALL xerbla( 'CHBGVX', -info )
395  RETURN
396  END IF
397 *
398 * Quick return if possible
399 *
400  m = 0
401  IF( n.EQ.0 )
402  \$ RETURN
403 *
404 * Form a split Cholesky factorization of B.
405 *
406  CALL cpbstf( uplo, n, kb, bb, ldbb, info )
407  IF( info.NE.0 ) THEN
408  info = n + info
409  RETURN
410  END IF
411 *
412 * Transform problem to standard eigenvalue problem.
413 *
414  CALL chbgst( jobz, uplo, n, ka, kb, ab, ldab, bb, ldbb, q, ldq,
415  \$ work, rwork, iinfo )
416 *
417 * Solve the standard eigenvalue problem.
418 * Reduce Hermitian band matrix to tridiagonal form.
419 *
420  indd = 1
421  inde = indd + n
422  indrwk = inde + n
423  indwrk = 1
424  IF( wantz ) THEN
425  vect = 'U'
426  ELSE
427  vect = 'N'
428  END IF
429  CALL chbtrd( vect, uplo, n, ka, ab, ldab, rwork( indd ),
430  \$ rwork( inde ), q, ldq, work( indwrk ), iinfo )
431 *
432 * If all eigenvalues are desired and ABSTOL is less than or equal
433 * to zero, then call SSTERF or CSTEQR. If this fails for some
434 * eigenvalue, then try SSTEBZ.
435 *
436  test = .false.
437  IF( indeig ) THEN
438  IF( il.EQ.1 .AND. iu.EQ.n ) THEN
439  test = .true.
440  END IF
441  END IF
442  IF( ( alleig .OR. test ) .AND. ( abstol.LE.zero ) ) THEN
443  CALL scopy( n, rwork( indd ), 1, w, 1 )
444  indee = indrwk + 2*n
445  CALL scopy( n-1, rwork( inde ), 1, rwork( indee ), 1 )
446  IF( .NOT.wantz ) THEN
447  CALL ssterf( n, w, rwork( indee ), info )
448  ELSE
449  CALL clacpy( 'A', n, n, q, ldq, z, ldz )
450  CALL csteqr( jobz, n, w, rwork( indee ), z, ldz,
451  \$ rwork( indrwk ), info )
452  IF( info.EQ.0 ) THEN
453  DO 10 i = 1, n
454  ifail( i ) = 0
455  10 CONTINUE
456  END IF
457  END IF
458  IF( info.EQ.0 ) THEN
459  m = n
460  GO TO 30
461  END IF
462  info = 0
463  END IF
464 *
465 * Otherwise, call SSTEBZ and, if eigenvectors are desired,
466 * call CSTEIN.
467 *
468  IF( wantz ) THEN
469  order = 'B'
470  ELSE
471  order = 'E'
472  END IF
473  indibl = 1
474  indisp = indibl + n
475  indiwk = indisp + n
476  CALL sstebz( range, order, n, vl, vu, il, iu, abstol,
477  \$ rwork( indd ), rwork( inde ), m, nsplit, w,
478  \$ iwork( indibl ), iwork( indisp ), rwork( indrwk ),
479  \$ iwork( indiwk ), info )
480 *
481  IF( wantz ) THEN
482  CALL cstein( n, rwork( indd ), rwork( inde ), m, w,
483  \$ iwork( indibl ), iwork( indisp ), z, ldz,
484  \$ rwork( indrwk ), iwork( indiwk ), ifail, info )
485 *
486 * Apply unitary matrix used in reduction to tridiagonal
487 * form to eigenvectors returned by CSTEIN.
488 *
489  DO 20 j = 1, m
490  CALL ccopy( n, z( 1, j ), 1, work( 1 ), 1 )
491  CALL cgemv( 'N', n, n, cone, q, ldq, work, 1, czero,
492  \$ z( 1, j ), 1 )
493  20 CONTINUE
494  END IF
495 *
496  30 CONTINUE
497 *
498 * If eigenvalues are not in order, then sort them, along with
499 * eigenvectors.
500 *
501  IF( wantz ) THEN
502  DO 50 j = 1, m - 1
503  i = 0
504  tmp1 = w( j )
505  DO 40 jj = j + 1, m
506  IF( w( jj ).LT.tmp1 ) THEN
507  i = jj
508  tmp1 = w( jj )
509  END IF
510  40 CONTINUE
511 *
512  IF( i.NE.0 ) THEN
513  itmp1 = iwork( indibl+i-1 )
514  w( i ) = w( j )
515  iwork( indibl+i-1 ) = iwork( indibl+j-1 )
516  w( j ) = tmp1
517  iwork( indibl+j-1 ) = itmp1
518  CALL cswap( n, z( 1, i ), 1, z( 1, j ), 1 )
519  IF( info.NE.0 ) THEN
520  itmp1 = ifail( i )
521  ifail( i ) = ifail( j )
522  ifail( j ) = itmp1
523  END IF
524  END IF
525  50 CONTINUE
526  END IF
527 *
528  RETURN
529 *
530 * End of CHBGVX
531 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine ssterf(N, D, E, INFO)
SSTERF
Definition: ssterf.f:86
subroutine sstebz(RANGE, ORDER, N, VL, VU, IL, IU, ABSTOL, D, E, M, NSPLIT, W, IBLOCK, ISPLIT, WORK, IWORK, INFO)
SSTEBZ
Definition: sstebz.f:273
subroutine ccopy(N, CX, INCX, CY, INCY)
CCOPY
Definition: ccopy.f:81
subroutine cswap(N, CX, INCX, CY, INCY)
CSWAP
Definition: cswap.f:81
subroutine cgemv(TRANS, M, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY)
CGEMV
Definition: cgemv.f:158
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
subroutine cstein(N, D, E, M, W, IBLOCK, ISPLIT, Z, LDZ, WORK, IWORK, IFAIL, INFO)
CSTEIN
Definition: cstein.f:182
subroutine cpbstf(UPLO, N, KD, AB, LDAB, INFO)
CPBSTF
Definition: cpbstf.f:153
subroutine chbtrd(VECT, UPLO, N, KD, AB, LDAB, D, E, Q, LDQ, WORK, INFO)
CHBTRD
Definition: chbtrd.f:163
subroutine chbgst(VECT, UPLO, N, KA, KB, AB, LDAB, BB, LDBB, X, LDX, WORK, RWORK, INFO)
CHBGST
Definition: chbgst.f:165
subroutine csteqr(COMPZ, N, D, E, Z, LDZ, WORK, INFO)
CSTEQR
Definition: csteqr.f:132
subroutine scopy(N, SX, INCX, SY, INCY)
SCOPY
Definition: scopy.f:82
Here is the call graph for this function:
Here is the caller graph for this function: