NAME

       lasq4 - lasq4: dqds step

SYNOPSIS

   Functions
       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.
       subroutine slasq4 (i0, n0, z, pp, n0in, dmin, dmin1, dmin2, dn, dn1, dn2, tau, ttype, g)
           SLASQ4 computes an approximation to the smallest eigenvalue using values of d from the
           previous transform. Used by sbdsqr.

Detailed Description

Function 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

                     I0 is INTEGER
                   First index.

           N0

                     N0 is INTEGER
                   Last index.

           Z

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

           PP

                     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

                     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

                     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.

       Further Details:

             CNST1 = 9/16

   subroutine slasq4 (integer i0, integer n0, real, dimension( * ) z, integer pp, integer n0in,
       real dmin, real dmin1, real dmin2, real dn, real dn1, real dn2, real tau, integer ttype,
       real g)
       SLASQ4 computes an approximation to the smallest eigenvalue using values of d from the
       previous transform. Used by sbdsqr.

       Purpose:

            SLASQ4 computes an approximation TAU to the smallest eigenvalue
            using values of d from the previous transform.

       Parameters
           I0

                     I0 is INTEGER
                   First index.

           N0

                     N0 is INTEGER
                   Last index.

           Z

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

           PP

                     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 REAL
                   Minimum value of d.

           DMIN1

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

           DMIN2

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

           DN

                     DN is REAL
                   d(N)

           DN1

                     DN1 is REAL
                   d(N-1)

           DN2

                     DN2 is REAL
                   d(N-2)

           TAU

                     TAU is REAL
                   This is the shift.

           TTYPE

                     TTYPE is INTEGER
                   Shift type.

           G

                     G is REAL
                   G is passed as an argument in order to save its value between
                   calls to SLASQ4.

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Further Details:

             CNST1 = 9/16

Author

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