LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ dlaed1()

subroutine dlaed1 ( integer  N,
double precision, dimension( * )  D,
double precision, dimension( ldq, * )  Q,
integer  LDQ,
integer, dimension( * )  INDXQ,
double precision  RHO,
integer  CUTPNT,
double precision, dimension( * )  WORK,
integer, dimension( * )  IWORK,
integer  INFO 
)

DLAED1 used by DSTEDC. Computes the updated eigensystem of a diagonal matrix after modification by a rank-one symmetric matrix. Used when the original matrix is tridiagonal.

Download DLAED1 + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 DLAED1 computes the updated eigensystem of a diagonal
 matrix after modification by a rank-one symmetric matrix.  This
 routine is used only for the eigenproblem which requires all
 eigenvalues and eigenvectors of a tridiagonal matrix.  DLAED7 handles
 the case in which eigenvalues only or eigenvalues and eigenvectors
 of a full symmetric matrix (which was reduced to tridiagonal form)
 are desired.

   T = Q(in) ( D(in) + RHO * Z*Z**T ) Q**T(in) = Q(out) * D(out) * Q**T(out)

    where Z = Q**T*u, u is a vector of length N with ones in the
    CUTPNT and CUTPNT + 1 th elements and zeros elsewhere.

    The eigenvectors of the original matrix are stored in Q, and the
    eigenvalues are in D.  The algorithm consists of three stages:

       The first stage consists of deflating the size of the problem
       when there are multiple eigenvalues or if there is a zero in
       the Z vector.  For each such occurrence the dimension of the
       secular equation problem is reduced by one.  This stage is
       performed by the routine DLAED2.

       The second stage consists of calculating the updated
       eigenvalues. This is done by finding the roots of the secular
       equation via the routine DLAED4 (as called by DLAED3).
       This routine also calculates the eigenvectors of the current
       problem.

       The final stage consists of computing the updated eigenvectors
       directly using the updated eigenvalues.  The eigenvectors for
       the current problem are multiplied with the eigenvectors from
       the overall problem.
Parameters
[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 eigenvalues of the rank-1-perturbed matrix.
         On exit, the eigenvalues of the repaired matrix.
[in,out]Q
          Q is DOUBLE PRECISION array, dimension (LDQ,N)
         On entry, the eigenvectors of the rank-1-perturbed matrix.
         On exit, the eigenvectors of the repaired tridiagonal matrix.
[in]LDQ
          LDQ is INTEGER
         The leading dimension of the array Q.  LDQ >= max(1,N).
[in,out]INDXQ
          INDXQ is INTEGER array, dimension (N)
         On entry, the permutation which separately sorts the two
         subproblems in D into ascending order.
         On exit, the permutation which will reintegrate the
         subproblems back into sorted order,
         i.e. D( INDXQ( I = 1, N ) ) will be in ascending order.
[in]RHO
          RHO is DOUBLE PRECISION
         The subdiagonal entry used to create the rank-1 modification.
[in]CUTPNT
          CUTPNT is INTEGER
         The location of the last eigenvalue in the leading sub-matrix.
         min(1,N) <= CUTPNT <= N/2.
[out]WORK
          WORK is DOUBLE PRECISION array, dimension (4*N + N**2)
[out]IWORK
          IWORK is INTEGER array, dimension (4*N)
[out]INFO
          INFO is INTEGER
          = 0:  successful exit.
          < 0:  if INFO = -i, the i-th argument had an illegal value.
          > 0:  if INFO = 1, an eigenvalue did not converge
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Contributors:
Jeff Rutter, Computer Science Division, University of California at Berkeley, USA
Modified by Francoise Tisseur, University of Tennessee

Definition at line 161 of file dlaed1.f.

163 *
164 * -- LAPACK computational routine --
165 * -- LAPACK is a software package provided by Univ. of Tennessee, --
166 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
167 *
168 * .. Scalar Arguments ..
169  INTEGER CUTPNT, INFO, LDQ, N
170  DOUBLE PRECISION RHO
171 * ..
172 * .. Array Arguments ..
173  INTEGER INDXQ( * ), IWORK( * )
174  DOUBLE PRECISION D( * ), Q( LDQ, * ), WORK( * )
175 * ..
176 *
177 * =====================================================================
178 *
179 * .. Local Scalars ..
180  INTEGER COLTYP, I, IDLMDA, INDX, INDXC, INDXP, IQ2, IS,
181  $ IW, IZ, K, N1, N2, ZPP1
182 * ..
183 * .. External Subroutines ..
184  EXTERNAL dcopy, dlaed2, dlaed3, dlamrg, xerbla
185 * ..
186 * .. Intrinsic Functions ..
187  INTRINSIC max, min
188 * ..
189 * .. Executable Statements ..
190 *
191 * Test the input parameters.
192 *
193  info = 0
194 *
195  IF( n.LT.0 ) THEN
196  info = -1
197  ELSE IF( ldq.LT.max( 1, n ) ) THEN
198  info = -4
199  ELSE IF( min( 1, n / 2 ).GT.cutpnt .OR. ( n / 2 ).LT.cutpnt ) THEN
200  info = -7
201  END IF
202  IF( info.NE.0 ) THEN
203  CALL xerbla( 'DLAED1', -info )
204  RETURN
205  END IF
206 *
207 * Quick return if possible
208 *
209  IF( n.EQ.0 )
210  $ RETURN
211 *
212 * The following values are integer pointers which indicate
213 * the portion of the workspace
214 * used by a particular array in DLAED2 and DLAED3.
215 *
216  iz = 1
217  idlmda = iz + n
218  iw = idlmda + n
219  iq2 = iw + n
220 *
221  indx = 1
222  indxc = indx + n
223  coltyp = indxc + n
224  indxp = coltyp + n
225 *
226 *
227 * Form the z-vector which consists of the last row of Q_1 and the
228 * first row of Q_2.
229 *
230  CALL dcopy( cutpnt, q( cutpnt, 1 ), ldq, work( iz ), 1 )
231  zpp1 = cutpnt + 1
232  CALL dcopy( n-cutpnt, q( zpp1, zpp1 ), ldq, work( iz+cutpnt ), 1 )
233 *
234 * Deflate eigenvalues.
235 *
236  CALL dlaed2( k, n, cutpnt, d, q, ldq, indxq, rho, work( iz ),
237  $ work( idlmda ), work( iw ), work( iq2 ),
238  $ iwork( indx ), iwork( indxc ), iwork( indxp ),
239  $ iwork( coltyp ), info )
240 *
241  IF( info.NE.0 )
242  $ GO TO 20
243 *
244 * Solve Secular Equation.
245 *
246  IF( k.NE.0 ) THEN
247  is = ( iwork( coltyp )+iwork( coltyp+1 ) )*cutpnt +
248  $ ( iwork( coltyp+1 )+iwork( coltyp+2 ) )*( n-cutpnt ) + iq2
249  CALL dlaed3( k, n, cutpnt, d, q, ldq, rho, work( idlmda ),
250  $ work( iq2 ), iwork( indxc ), iwork( coltyp ),
251  $ work( iw ), work( is ), info )
252  IF( info.NE.0 )
253  $ GO TO 20
254 *
255 * Prepare the INDXQ sorting permutation.
256 *
257  n1 = k
258  n2 = n - k
259  CALL dlamrg( n1, n2, d, 1, -1, indxq )
260  ELSE
261  DO 10 i = 1, n
262  indxq( i ) = i
263  10 CONTINUE
264  END IF
265 *
266  20 CONTINUE
267  RETURN
268 *
269 * End of DLAED1
270 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine dlamrg(N1, N2, A, DTRD1, DTRD2, INDEX)
DLAMRG creates a permutation list to merge the entries of two independently sorted sets into a single...
Definition: dlamrg.f:99
subroutine dlaed2(K, N, N1, D, Q, LDQ, INDXQ, RHO, Z, DLAMDA, W, Q2, INDX, INDXC, INDXP, COLTYP, INFO)
DLAED2 used by DSTEDC. Merges eigenvalues and deflates secular equation. Used when the original matri...
Definition: dlaed2.f:212
subroutine dlaed3(K, N, N1, D, Q, LDQ, RHO, DLAMDA, Q2, INDX, CTOT, W, S, INFO)
DLAED3 used by DSTEDC. Finds the roots of the secular equation and updates the eigenvectors....
Definition: dlaed3.f:185
subroutine dcopy(N, DX, INCX, DY, INCY)
DCOPY
Definition: dcopy.f:82
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