DLAED3(1) LAPACK routine (version 3.2) DLAED3(1)NAME
DLAED3 - finds the roots of the secular equation, as defined by the
values in D, W, and RHO, between 1 and K
SUBROUTINE DLAED3( K, N, N1, D, Q, LDQ, RHO, DLAMDA, Q2, INDX, CTOT, W,
S, INFO )
INTEGER INFO, K, LDQ, N, N1
DOUBLE PRECISION RHO
INTEGER CTOT( * ), INDX( * )
DOUBLE PRECISION D( * ), DLAMDA( * ), Q( LDQ, * ), Q2( * ),
S( * ), W( * )
DLAED3 finds the roots of the secular equation, as defined by the val‐
ues in D, W, and RHO, between 1 and K. It makes the appropriate calls
to DLAED4 and then updates the eigenvectors by multiplying the matrix
of eigenvectors of the pair of eigensystems being combined by the
matrix of eigenvectors of the K-by-K system which is solved here.
This code makes very mild assumptions about floating point arithmetic.
It will work on machines with a guard digit in add/subtract, or on
those binary machines without guard digits which subtract like the Cray
X-MP, Cray Y-MP, Cray C-90, or Cray-2. It could conceivably fail on
hexadecimal or decimal machines without guard digits, but we know of
K (input) INTEGER
The number of terms in the rational function to be solved by
DLAED4. K >= 0.
N (input) INTEGER
The number of rows and columns in the Q matrix. N >= K (defla‐
tion may result in N>K).
N1 (input) INTEGER
The location of the last eigenvalue in the leading submatrix.
min(1,N) <= N1 <= N/2.
D (output) DOUBLE PRECISION array, dimension (N)
D(I) contains the updated eigenvalues for 1 <= I <= K.
Q (output) DOUBLE PRECISION array, dimension (LDQ,N)
Initially the first K columns are used as workspace. On output
the columns 1 to K contain the updated eigenvectors.
LDQ (input) INTEGER
The leading dimension of the array Q. LDQ >= max(1,N).
RHO (input) DOUBLE PRECISION
The value of the parameter in the rank one update equation.
RHO >= 0 required.
DLAMDA (input/output) DOUBLE PRECISION array, dimension (K)
The first K elements of this array contain the old roots of the
deflated updating problem. These are the poles of the secular
equation. May be changed on output by having lowest order bit
set to zero on Cray X-MP, Cray Y-MP, Cray-2, or Cray C-90, as
Q2 (input) DOUBLE PRECISION array, dimension (LDQ2, N)
The first K columns of this matrix contain the non-deflated
eigenvectors for the split problem.
INDX (input) INTEGER array, dimension (N)
The permutation used to arrange the columns of the deflated Q
matrix into three groups (see DLAED2). The rows of the eigen‐
vectors found by DLAED4 must be likewise permuted before the
matrix multiply can take place.
CTOT (input) INTEGER array, dimension (4)
A count of the total number of the various types of columns in
Q, as described in INDX. The fourth column type is any column
which has been deflated.
W (input/output) DOUBLE PRECISION array, dimension (K)
The first K elements of this array contain the components of
the deflation-adjusted updating vector. Destroyed on output.
S (workspace) DOUBLE PRECISION array, dimension (N1 + 1)*K
Will contain the eigenvectors of the repaired matrix which will
be multiplied by the previously accumulated eigenvectors to
update the system.
LDS (input) INTEGER
The leading dimension of S. LDS >= max(1,K).
INFO (output) 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
Based on contributions by
Jeff Rutter, Computer Science Division, University of California
at Berkeley, USA
Modified by Francoise Tisseur, University of Tennessee.
LAPACK routine (version 3.2) November 2008 DLAED3(1)