dlasq3 (l)  Linux Man Pages
dlasq3: checks for deflation, computes a shift (TAU) and calls dqds
Command to display dlasq3
manual in Linux: $ man l dlasq3
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.
Pages related to dlasq3
 dlasq3 (3)
 dlasq1 (l)  computes the singular values of a real NbyN bidiagonal matrix with diagonal D and offdiagonal E
 dlasq2 (l)  computes all the eigenvalues of the symmetric positive definite tridiagonal matrix associated with the qd array Z to high relative accuracy are computed to high relative accuracy, in the absence of denormalization, underflow and overflow
 dlasq4 (l)  computes an approximation TAU to the smallest eigenvalue using values of d from the previous transform
 dlasq5 (l)  computes one dqds transform in pingpong form, one version for IEEE machines another for non IEEE machines
 dlasq6 (l)  computes one dqd (shift equal to zero) transform in pingpong form, with protection against underflow and overflow
 dlas2 (l)  computes the singular values of the 2by2 matrix [ F G ] [ 0 H ]
 dlascl (l)  multiplies the M by N real matrix A by the real scalar CTO/CFROM
 dlascl2 (l)  performs a diagonal scaling on a vector
 dlasd0 (l)  a divide and conquer approach, DLASD0 computes the singular value decomposition (SVD) of a real upper bidiagonal NbyM matrix B with diagonal D and offdiagonal E, where M = N + SQRE