SLAEDA(l) ) SLAEDA(l)NAME
SLAEDA - compute the Z vector corresponding to the merge step in the
CURLVLth step of the merge process with TLVLS steps for the CURPBMth
problem
SYNOPSIS
SUBROUTINE SLAEDA( N, TLVLS, CURLVL, CURPBM, PRMPTR, PERM, GIVPTR, GIV‐
COL, GIVNUM, Q, QPTR, Z, ZTEMP, INFO )
INTEGER CURLVL, CURPBM, INFO, N, TLVLS
INTEGER GIVCOL( 2, * ), GIVPTR( * ), PERM( * ), PRMPTR( * ),
QPTR( * )
REAL GIVNUM( 2, * ), Q( * ), Z( * ), ZTEMP( * )
PURPOSE
SLAEDA computes the Z vector corresponding to the merge step in the
CURLVLth step of the merge process with TLVLS steps for the CURPBMth
problem.
ARGUMENTS
N (input) INTEGER
The dimension of the symmetric tridiagonal matrix. N >= 0.
TLVLS (input) INTEGER
The total number of merging levels in the overall divide and
conquer tree.
CURLVL (input) INTEGER The current level in the overall merge
routine, 0 <= curlvl <= tlvls.
CURPBM (input) INTEGER The current problem in the current level
in the overall merge routine (counting from upper left to lower
right).
PRMPTR (input) INTEGER array, dimension (N lg N) Contains a list
of pointers which indicate where in PERM a level's permutation
is stored. PRMPTR(i+1) - PRMPTR(i) indicates the size of the
permutation and incidentally the size of the full, non-deflated
problem.
PERM (input) INTEGER array, dimension (N lg N)
Contains the permutations (from deflation and sorting) to be
applied to each eigenblock.
GIVPTR (input) INTEGER array, dimension (N lg N) Contains a list
of pointers which indicate where in GIVCOL a level's Givens
rotations are stored. GIVPTR(i+1) - GIVPTR(i) indicates the
number of Givens rotations.
GIVCOL (input) INTEGER array, dimension (2, N lg N) Each pair of
numbers indicates a pair of columns to take place in a Givens
rotation.
GIVNUM (input) REAL array, dimension (2, N lg N) Each number
indicates the S value to be used in the corresponding Givens
rotation.
Q (input) REAL array, dimension (N**2)
Contains the square eigenblocks from previous levels, the start‐
ing positions for blocks are given by QPTR.
QPTR (input) INTEGER array, dimension (N+2)
Contains a list of pointers which indicate where in Q an eigen‐
block is stored. SQRT( QPTR(i+1) - QPTR(i) ) indicates the size
of the block.
Z (output) REAL array, dimension (N)
On output this vector contains the updating vector (the last row
of the first sub-eigenvector matrix and the first row of the
second sub-eigenvector matrix).
ZTEMP (workspace) REAL array, dimension (N)
INFO (output) INTEGER
= 0: successful exit.
< 0: if INFO = -i, the i-th argument had an illegal value.
FURTHER DETAILS
Based on contributions by
Jeff Rutter, Computer Science Division, University of California
at Berkeley, USA
LAPACK version 3.0 15 June 2000 SLAEDA(l)
