man dlasq3 (Fonctions bibliothèques) - check for deflation, computes a shift (TAU) and calls dqds

NAME

DLASQ3 - check for deflation, computes a shift (TAU) and calls dqds

SUBROUTINE DLASQ3(: I0, N0, Z, PP, DMIN, SIGMA, DESIG, QMAX, NFAIL, ITER, NDIV, IEEE )
: LOGICAL IEEE
: INTEGER I0, ITER, N0, NDIV, NFAIL, PP
: DOUBLE PRECISION DESIG, DMIN, QMAX, SIGMA
: DOUBLE PRECISION Z( * )

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.

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.
TTYPE (output) INTEGER: Shift type.
IEEE (input) LOGICAL: Flag for IEEE or non IEEE arithmetic (passed to DLASQ5).