slaeda(3)

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, GIVCOL, 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 lev

el'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 sort

ing) 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 lev

el's Givens rotations are stored. GIVPTR(i+1) - GIVPTR(i) indi

cates 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 lev

els, the starting 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 eigenblock 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 ille

gal 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(3)