NAME¶

DLAZQ3 - for deflation, computes a shift (TAU) and calls dqds

SYNOPSIS¶

SUBROUTINE DLAZQ3(

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 DOUBLE PRECISION DESIG, DMIN, DMIN1, DMIN2, DN, DN1, DN2, QMAX, SIGMA, TAU DOUBLE PRECISION Z( * )

PURPOSE¶

DLAZQ3 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) INTEGER

PP=0 for ping, PP=1 for pong.

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. TTYPE is passed as an argument in order to save its value between calls to DLAZQ3

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 DLAZQ3

This is a thread safe version of DLASQ3, which passes TTYPE, DMIN1, DMIN2, DN, DN1. DN2 and TAU through the argument list in place of declaring them in a SAVE statment.