SLAZQ3(1) LAPACK auxiliary routine (version 3.1) SLAZQ3(1)NAME
SLAZQ3 - for deflation, computes a shift (TAU) and calls dqds
SYNOPSIS
SUBROUTINE SLAZQ3( I0, N0, Z, PP, DMIN, SIGMA, DESIG, QMAX, NFAIL,
ITER, NDIV, IEEE, TTYPE, DMIN1, DMIN2, DN, DN1, DN2,
TAU )
LOGICAL IEEE
INTEGER I0, ITER, N0, NDIV, NFAIL, PP, TTYPE
REAL DESIG, DMIN, DMIN1, DMIN2, DN, DN1, DN2, QMAX,
SIGMA, TAU
REAL Z( * )
PURPOSE
SLAZQ3 checks for deflation, computes a shift (TAU) and calls dqds. In
case of failure it changes shifts, and tries again until output is pos‐
itive.
ARGUMENTS
I0 (input) INTEGER
First index.
N0 (input) INTEGER
Last index.
Z (input) REAL array, dimension ( 4*N )
Z holds the qd array.
PP (input) INTEGER
PP=0 for ping, PP=1 for pong.
DMIN (output) REAL
Minimum value of d.
SIGMA (output) REAL
Sum of shifts used in current segment.
DESIG (input/output) REAL
Lower order part of SIGMA
QMAX (input) REAL
Maximum value of q.
NFAIL (output) INTEGER
Number of times shift was too big.
ITER (output) INTEGER
Number of iterations.
NDIV (output) INTEGER
Number of divisions.
IEEE (input) LOGICAL
Flag for IEEE or non IEEE arithmetic (passed to SLASQ5).
TTYPE (input/output) INTEGER
Shift type. TTYPE is passed as an argument in order to save its
value between calls to SLAZQ3
DMIN1 (input/output) REAL
DMIN2 (input/output) REAL DN (input/output) REAL DN1
(input/output) REAL DN2 (input/output) REAL TAU
(input/output) REAL These are passed as arguments in order to
save their values between calls to SLAZQ3
This is a thread safe version of SLASQ3, which passes TTYPE,
DMIN1, DMIN2, DN, DN1. DN2 and TAU through the argument list in
place of declaring them in a SAVE statment.
LAPACK auxiliary routine (versioOctober 2006 SLAZQ3(1)