dlasq4.f

Section: LAPACK (3)
Updated: Tue Nov 14 2017
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NAME

dlasq4.f

SYNOPSIS

Functions/Subroutines

subroutine dlasq4 (I0, N0, Z, PP, N0IN, DMIN, DMIN1, DMIN2, DN, DN1, DN2, TAU, TTYPE, G)
DLASQ4 computes an approximation to the smallest eigenvalue using values of d from the previous transform. Used by sbdsqr.

Function/Subroutine Documentation

subroutine dlasq4 (integer I0, integer N0, double precision, dimension( * ) Z, integer PP, integer N0IN, double precision DMIN, double precision DMIN1, double precision DMIN2, double precision DN, double precision DN1, double precision DN2, double precision TAU, integer TTYPE, double precision G)

DLASQ4 computes an approximation to the smallest eigenvalue using values of d from the previous transform. Used by sbdsqr.

Purpose:

 DLASQ4 computes an approximation TAU to the smallest eigenvalue
 using values of d from the previous transform.

Parameters:

          I0 is INTEGER
        First index.

          N0 is INTEGER
        Last index.

          Z is DOUBLE PRECISION array, dimension ( 4*N0 )
        Z holds the qd array.

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

N0IN

          N0IN is INTEGER
        The value of N0 at start of EIGTEST.

DMIN

          DMIN is DOUBLE PRECISION
        Minimum value of d.

DMIN1

          DMIN1 is DOUBLE PRECISION
        Minimum value of d, excluding D( N0 ).

DMIN2

          DMIN2 is DOUBLE PRECISION
        Minimum value of d, excluding D( N0 ) and D( N0-1 ).

          DN is DOUBLE PRECISION
        d(N)

DN1

          DN1 is DOUBLE PRECISION
        d(N-1)

DN2

          DN2 is DOUBLE PRECISION
        d(N-2)

TAU

          TAU is DOUBLE PRECISION
        This is the shift.

TTYPE

          TTYPE is INTEGER
        Shift type.

          G is DOUBLE PRECISION
        G is passed as an argument in order to save its value between
        calls to DLASQ4.

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

: June 2016

Further Details:

  CNST1 = 9/16

Definition at line 153 of file dlasq4.f.

Author

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