NAME¶

SLASQ3 - checks for deflation, computes a shift (TAU) and calls dqds

SYNOPSIS¶

SUBROUTINE SLASQ3(

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 REAL DESIG, DMIN, DMIN1, DMIN2, DN, DN1, DN2, G, QMAX, SIGMA, TAU REAL Z( * )

PURPOSE¶

SLASQ3 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) REAL 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) 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. DMIN1, DMIN2, DN, DN1, DN2, G, TAU (input/output) REAL These are passed as arguments in order to save their values between calls to SLASQ3.