lasq4(3) LAPACK lasq4(3)

lasq4 - lasq4: dqds step


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.

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

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

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Fri Aug 9 2024 02:33:22 Version 3.12.0