LAPACK  3.6.1
LAPACK: Linear Algebra PACKage
subroutine zlaed0 ( integer  QSIZ,
integer  N,
double precision, dimension( * )  D,
double precision, dimension( * )  E,
complex*16, dimension( ldq, * )  Q,
integer  LDQ,
complex*16, dimension( ldqs, * )  QSTORE,
integer  LDQS,
double precision, dimension( * )  RWORK,
integer, dimension( * )  IWORK,
integer  INFO 
)

ZLAED0 used by sstedc. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

Download ZLAED0 + dependencies [TGZ] [ZIP] [TXT]

Purpose: 
 Using the divide and conquer method, ZLAED0 computes all eigenvalues
 of a symmetric tridiagonal matrix which is one diagonal block of
 those from reducing a dense or band Hermitian matrix and
 corresponding eigenvectors of the dense or band matrix.
Parameters
[in]QSIZ
          QSIZ is INTEGER
         The dimension of the unitary matrix used to reduce
         the full matrix to tridiagonal form.  QSIZ >= N if ICOMPQ = 1.
[in]N
          N is INTEGER
         The dimension of the symmetric tridiagonal matrix.  N >= 0.
[in,out]D
          D is DOUBLE PRECISION array, dimension (N)
         On entry, the diagonal elements of the tridiagonal matrix.
         On exit, the eigenvalues in ascending order.
[in,out]E
          E is DOUBLE PRECISION array, dimension (N-1)
         On entry, the off-diagonal elements of the tridiagonal matrix.
         On exit, E has been destroyed.
[in,out]Q
          Q is COMPLEX*16 array, dimension (LDQ,N)
         On entry, Q must contain an QSIZ x N matrix whose columns
         unitarily orthonormal. It is a part of the unitary matrix
         that reduces the full dense Hermitian matrix to a
         (reducible) symmetric tridiagonal matrix.
[in]LDQ
          LDQ is INTEGER
         The leading dimension of the array Q.  LDQ >= max(1,N).
[out]IWORK
          IWORK is INTEGER array,
         the dimension of IWORK must be at least
                      6 + 6*N + 5*N*lg N
                      ( lg( N ) = smallest integer k
                                  such that 2^k >= N )
[out]RWORK
          RWORK is DOUBLE PRECISION array,
                               dimension (1 + 3*N + 2*N*lg N + 3*N**2)
                        ( lg( N ) = smallest integer k
                                    such that 2^k >= N )
[out]QSTORE
          QSTORE is COMPLEX*16 array, dimension (LDQS, N)
         Used to store parts of
         the eigenvector matrix when the updating matrix multiplies
         take place.
[in]LDQS
          LDQS is INTEGER
         The leading dimension of the array QSTORE.
         LDQS >= max(1,N).
[out]INFO
          INFO is INTEGER
          = 0:  successful exit.
          < 0:  if INFO = -i, the i-th argument had an illegal value.
          > 0:  The algorithm failed to compute an eigenvalue while
                working on the submatrix lying in rows and columns
                INFO/(N+1) through mod(INFO,N+1).
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
September 2012

Definition at line 147 of file zlaed0.f.

147 *
148 * -- LAPACK computational routine (version 3.4.2) --
149 * -- LAPACK is a software package provided by Univ. of Tennessee, --
150 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
151 * September 2012
152 *
153 * .. Scalar Arguments ..
154  INTEGER info, ldq, ldqs, n, qsiz
155 * ..
156 * .. Array Arguments ..
157  INTEGER iwork( * )
158  DOUBLE PRECISION d( * ), e( * ), rwork( * )
159  COMPLEX*16 q( ldq, * ), qstore( ldqs, * )
160 * ..
161 *
162 * =====================================================================
163 *
164 * Warning: N could be as big as QSIZ!
165 *
166 * .. Parameters ..
167  DOUBLE PRECISION two
168  parameter ( two = 2.d+0 )
169 * ..
170 * .. Local Scalars ..
171  INTEGER curlvl, curprb, curr, i, igivcl, igivnm,
172  $ igivpt, indxq, iperm, iprmpt, iq, iqptr, iwrem,
173  $ j, k, lgn, ll, matsiz, msd2, smlsiz, smm1,
174  $ spm1, spm2, submat, subpbs, tlvls
175  DOUBLE PRECISION temp
176 * ..
177 * .. External Subroutines ..
178  EXTERNAL dcopy, dsteqr, xerbla, zcopy, zlacrm, zlaed7
179 * ..
180 * .. External Functions ..
181  INTEGER ilaenv
182  EXTERNAL ilaenv
183 * ..
184 * .. Intrinsic Functions ..
185  INTRINSIC abs, dble, int, log, max
186 * ..
187 * .. Executable Statements ..
188 *
189 * Test the input parameters.
190 *
191  info = 0
192 *
193 * IF( ICOMPQ .LT. 0 .OR. ICOMPQ .GT. 2 ) THEN
194 * INFO = -1
195 * ELSE IF( ( ICOMPQ .EQ. 1 ) .AND. ( QSIZ .LT. MAX( 0, N ) ) )
196 * $ THEN
197  IF( qsiz.LT.max( 0, n ) ) THEN
198  info = -1
199  ELSE IF( n.LT.0 ) THEN
200  info = -2
201  ELSE IF( ldq.LT.max( 1, n ) ) THEN
202  info = -6
203  ELSE IF( ldqs.LT.max( 1, n ) ) THEN
204  info = -8
205  END IF
206  IF( info.NE.0 ) THEN
207  CALL xerbla( 'ZLAED0', -info )
208  RETURN
209  END IF
210 *
211 * Quick return if possible
212 *
213  IF( n.EQ.0 )
214  $ RETURN
215 *
216  smlsiz = ilaenv( 9, 'ZLAED0', ' ', 0, 0, 0, 0 )
217 *
218 * Determine the size and placement of the submatrices, and save in
219 * the leading elements of IWORK.
220 *
221  iwork( 1 ) = n
222  subpbs = 1
223  tlvls = 0
224  10 CONTINUE
225  IF( iwork( subpbs ).GT.smlsiz ) THEN
226  DO 20 j = subpbs, 1, -1
227  iwork( 2*j ) = ( iwork( j )+1 ) / 2
228  iwork( 2*j-1 ) = iwork( j ) / 2
229  20 CONTINUE
230  tlvls = tlvls + 1
231  subpbs = 2*subpbs
232  GO TO 10
233  END IF
234  DO 30 j = 2, subpbs
235  iwork( j ) = iwork( j ) + iwork( j-1 )
236  30 CONTINUE
237 *
238 * Divide the matrix into SUBPBS submatrices of size at most SMLSIZ+1
239 * using rank-1 modifications (cuts).
240 *
241  spm1 = subpbs - 1
242  DO 40 i = 1, spm1
243  submat = iwork( i ) + 1
244  smm1 = submat - 1
245  d( smm1 ) = d( smm1 ) - abs( e( smm1 ) )
246  d( submat ) = d( submat ) - abs( e( smm1 ) )
247  40 CONTINUE
248 *
249  indxq = 4*n + 3
250 *
251 * Set up workspaces for eigenvalues only/accumulate new vectors
252 * routine
253 *
254  temp = log( dble( n ) ) / log( two )
255  lgn = int( temp )
256  IF( 2**lgn.LT.n )
257  $ lgn = lgn + 1
258  IF( 2**lgn.LT.n )
259  $ lgn = lgn + 1
260  iprmpt = indxq + n + 1
261  iperm = iprmpt + n*lgn
262  iqptr = iperm + n*lgn
263  igivpt = iqptr + n + 2
264  igivcl = igivpt + n*lgn
265 *
266  igivnm = 1
267  iq = igivnm + 2*n*lgn
268  iwrem = iq + n**2 + 1
269 * Initialize pointers
270  DO 50 i = 0, subpbs
271  iwork( iprmpt+i ) = 1
272  iwork( igivpt+i ) = 1
273  50 CONTINUE
274  iwork( iqptr ) = 1
275 *
276 * Solve each submatrix eigenproblem at the bottom of the divide and
277 * conquer tree.
278 *
279  curr = 0
280  DO 70 i = 0, spm1
281  IF( i.EQ.0 ) THEN
282  submat = 1
283  matsiz = iwork( 1 )
284  ELSE
285  submat = iwork( i ) + 1
286  matsiz = iwork( i+1 ) - iwork( i )
287  END IF
288  ll = iq - 1 + iwork( iqptr+curr )
289  CALL dsteqr( 'I', matsiz, d( submat ), e( submat ),
290  $ rwork( ll ), matsiz, rwork, info )
291  CALL zlacrm( qsiz, matsiz, q( 1, submat ), ldq, rwork( ll ),
292  $ matsiz, qstore( 1, submat ), ldqs,
293  $ rwork( iwrem ) )
294  iwork( iqptr+curr+1 ) = iwork( iqptr+curr ) + matsiz**2
295  curr = curr + 1
296  IF( info.GT.0 ) THEN
297  info = submat*( n+1 ) + submat + matsiz - 1
298  RETURN
299  END IF
300  k = 1
301  DO 60 j = submat, iwork( i+1 )
302  iwork( indxq+j ) = k
303  k = k + 1
304  60 CONTINUE
305  70 CONTINUE
306 *
307 * Successively merge eigensystems of adjacent submatrices
308 * into eigensystem for the corresponding larger matrix.
309 *
310 * while ( SUBPBS > 1 )
311 *
312  curlvl = 1
313  80 CONTINUE
314  IF( subpbs.GT.1 ) THEN
315  spm2 = subpbs - 2
316  DO 90 i = 0, spm2, 2
317  IF( i.EQ.0 ) THEN
318  submat = 1
319  matsiz = iwork( 2 )
320  msd2 = iwork( 1 )
321  curprb = 0
322  ELSE
323  submat = iwork( i ) + 1
324  matsiz = iwork( i+2 ) - iwork( i )
325  msd2 = matsiz / 2
326  curprb = curprb + 1
327  END IF
328 *
329 * Merge lower order eigensystems (of size MSD2 and MATSIZ - MSD2)
330 * into an eigensystem of size MATSIZ. ZLAED7 handles the case
331 * when the eigenvectors of a full or band Hermitian matrix (which
332 * was reduced to tridiagonal form) are desired.
333 *
334 * I am free to use Q as a valuable working space until Loop 150.
335 *
336  CALL zlaed7( matsiz, msd2, qsiz, tlvls, curlvl, curprb,
337  $ d( submat ), qstore( 1, submat ), ldqs,
338  $ e( submat+msd2-1 ), iwork( indxq+submat ),
339  $ rwork( iq ), iwork( iqptr ), iwork( iprmpt ),
340  $ iwork( iperm ), iwork( igivpt ),
341  $ iwork( igivcl ), rwork( igivnm ),
342  $ q( 1, submat ), rwork( iwrem ),
343  $ iwork( subpbs+1 ), info )
344  IF( info.GT.0 ) THEN
345  info = submat*( n+1 ) + submat + matsiz - 1
346  RETURN
347  END IF
348  iwork( i / 2+1 ) = iwork( i+2 )
349  90 CONTINUE
350  subpbs = subpbs / 2
351  curlvl = curlvl + 1
352  GO TO 80
353  END IF
354 *
355 * end while
356 *
357 * Re-merge the eigenvalues/vectors which were deflated at the final
358 * merge step.
359 *
360  DO 100 i = 1, n
361  j = iwork( indxq+i )
362  rwork( i ) = d( j )
363  CALL zcopy( qsiz, qstore( 1, j ), 1, q( 1, i ), 1 )
364  100 CONTINUE
365  CALL dcopy( n, rwork, 1, d, 1 )
366 *
367  RETURN
368 *
369 * End of ZLAED0
370 *
dcopy
subroutine dcopy(N, DX, INCX, DY, INCY)
DCOPY
Definition: dcopy.f:53
zcopy
subroutine zcopy(N, ZX, INCX, ZY, INCY)
ZCOPY
Definition: zcopy.f:52
zlaed7
subroutine zlaed7(N, CUTPNT, QSIZ, TLVLS, CURLVL, CURPBM, D, Q, LDQ, RHO, INDXQ, QSTORE, QPTR, PRMPTR, PERM, GIVPTR, GIVCOL, GIVNUM, WORK, RWORK, IWORK, INFO)
ZLAED7 used by sstedc. Computes the updated eigensystem of a diagonal matrix after modification by a ...
Definition: zlaed7.f:251
dsteqr
subroutine dsteqr(COMPZ, N, D, E, Z, LDZ, WORK, INFO)
DSTEQR
Definition: dsteqr.f:133
xerbla
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
ilaenv
integer function ilaenv(ISPEC, NAME, OPTS, N1, N2, N3, N4)
Definition: tstiee.f:83
zlacrm
subroutine zlacrm(M, N, A, LDA, B, LDB, C, LDC, RWORK)
ZLACRM multiplies a complex matrix by a square real matrix.
Definition: zlacrm.f:116

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