NAME
DLASQ3 - checks for deflation, computes a shift (TAU) and calls dqds
SYNOPSIS
- SUBROUTINE DLASQ3(
-
I0, N0, Z, PP, DMIN, SIGMA, DESIG, QMAX, NFAIL, ITER, NDIV, IEEE, TTYPE, DMIN1, DMIN2, DN, DN1, DN2, G, TAU )
- LOGICAL
-
IEEE
- INTEGER
-
I0, ITER, N0, NDIV, NFAIL, PP
- DOUBLE
-
PRECISION DESIG, DMIN, DMIN1, DMIN2, DN, DN1, DN2, G, QMAX, SIGMA, TAU
- DOUBLE
-
PRECISION Z( * )
PURPOSE
DLASQ3 checks for deflation, computes a shift (TAU) and calls dqds. In case of failure it changes shifts, and tries again until output is positive.
ARGUMENTS
- I0 (input) INTEGER
-
First index.
- N0 (input) INTEGER
-
Last index.
- Z (input) DOUBLE PRECISION array, dimension ( 4*N )
-
Z holds the qd array.
- PP (input/output) INTEGER
-
PP=0 for ping, PP=1 for pong. PP=2 indicates that flipping was applied to the Z array and that the initial tests for deflation should not be performed.
- DMIN (output) DOUBLE PRECISION
-
Minimum value of d.
- SIGMA (output) DOUBLE PRECISION
-
Sum of shifts used in current segment.
- DESIG (input/output) DOUBLE PRECISION
-
Lower order part of SIGMA
- QMAX (input) DOUBLE PRECISION
-
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 DLASQ5).
- TTYPE (input/output) INTEGER
-
Shift type. DMIN1, DMIN2, DN, DN1, DN2, G, TAU (input/output) DOUBLE PRECISION These are passed as arguments in order to save their values between calls to DLASQ3.