CLAMSH(l) ) CLAMSH(l)NAME
CLAMSH - send multiple shifts through a small (single node) matrix to
see how consecutive small subdiagonal elements are modified by subse‐
quent shifts in an effort to maximize the number of bulges that can be
sent through
SYNOPSIS
SUBROUTINE CLAMSH( S, LDS, NBULGE, JBLK, H, LDH, N, ULP )
INTEGER JBLK, LDH, LDS, N, NBULGE
REAL ULP
COMPLEX H( LDH, * ), S( LDS, * )
PURPOSE
CLAMSH sends multiple shifts through a small (single node) matrix to
see how consecutive small subdiagonal elements are modified by subse‐
quent shifts in an effort to maximize the number of bulges that can be
sent through. CLAMSH should only be called when there are multiple
shifts/bulges
(NBULGE > 1) and the first shift is starting in the middle of an
unreduced Hessenberg matrix because of two or more consecutive
small subdiagonal elements.
ARGUMENTS
S (local input/output) COMPLEX array, ( LDS,* )
On entry, the matrix of shifts. Only the 2x2 diagonal of S is
referenced. It is assumed that S has JBLK double shifts (size
2). On exit, the data is rearranged in the best order for
applying.
LDS (local input) INTEGER
On entry, the leading dimension of S. Unchanged on exit. 1 <
NBULGE <= JBLK <= LDS/2
NBULGE (local input/output) INTEGER
On entry, the number of bulges to send through H ( >1 ).
NBULGE should be less than the maximum determined (JBLK). 1 <
NBULGE <= JBLK <= LDS/2 On exit, the maximum number of bulges
that can be sent through.
JBLK (local input) INTEGER
On entry, the number of shifts determined for S. Unchanged on
exit.
H (local input/output) COMPLEX array ( LDH,N )
On entry, the local matrix to apply the shifts on. H should be
aligned so that the starting row is 2. On exit, the data is
destroyed.
LDH (local input) INTEGER
On entry, the leading dimension of H. Unchanged on exit.
N (local input) INTEGER
On entry, the size of H. If all the bulges are expected to go
through, N should be at least 4*NBULGE+2. Otherwise, NBULGE
may be reduced by this routine.
ULP (local input) REAL
On entry, machine precision Unchanged on exit.
FURTHER DETAILS
Implemented by: M. Fahey, May 28, 1999
ScaLAPACK version 1.7 13 August 2001 CLAMSH(l)
