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# Manual Reference Pages  -  CLAMSH (l)

### NAME

CLAMSH - 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
Purpose
Arguments
Further Details

### 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 subsequent 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

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 ScaLAPACK version 1.7 CLAMSH (l) 13 August 2001

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