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SLAMSH(l) LAPACK auxiliary routine (version 1.5) SLAMSH(l)

NAME

SLAMSH - send multiple shifts through a small (single node) matrix to see how consecutive small subdiagonal elements are modified by subsequent shifts in an effort to maximize the number of bulges that can be sent through

SYNOPSIS

( S, LDS, NBULGE, JBLK, H, LDH, N, ULP )

INTEGER LDS, NBULGE, JBLK, LDH, N REAL ULP REAL S(LDS,*), H(LDH,*)

PURPOSE

SLAMSH sends multiple shifts through a small (single node) matrix to
see how consecutive small subdiagonal elements are modified by
subsequent shifts in an effort to maximize the number of bulges
that can be sent through. SLAMSH 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

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.
On entry, the leading dimension of S. Unchanged on exit. 1 < NBULGE <= JBLK <= LDS/2
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.
On entry, the number of shifts determined for S. Unchanged on exit.
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.
On entry, the leading dimension of S. Unchanged on exit.
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.
On entry, machine precision Unchanged on exit.

Implemented by: G. Henry, May 1, 1997

12 May 1997 LAPACK version 1.5