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lasq3 - Man Page

lasq3: dqds step

subroutine dlasq3 (i0, n0, z, pp, dmin, sigma, desig, qmax, nfail, iter, ndiv, ieee, ttype, dmin1, dmin2, dn, dn1, dn2, g, tau)
DLASQ3 checks for deflation, computes a shift and calls dqds. Used by sbdsqr.
subroutine slasq3 (i0, n0, z, pp, dmin, sigma, desig, qmax, nfail, iter, ndiv, ieee, ttype, dmin1, dmin2, dn, dn1, dn2, g, tau)
SLASQ3 checks for deflation, computes a shift and calls dqds. Used by sbdsqr.

Detailed Description

Function Documentation

subroutine dlasq3 (integer i0, integer n0, double precision, dimension( * ) z, integer pp, double precision dmin, double precision sigma, double precision desig, double precision qmax, integer nfail, integer iter, integer ndiv, logical ieee, integer ttype, double precision dmin1, double precision dmin2, double precision dn, double precision dn1, double precision dn2, double precision g, double precision tau)

DLASQ3 checks for deflation, computes a shift and calls dqds. Used by sbdsqr.

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.

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.
         PP=2 indicates that flipping was applied to the Z array
         and that the initial tests for deflation should not be
         performed.

DMIN

          DMIN is DOUBLE PRECISION
         Minimum value of d.

SIGMA

          SIGMA is DOUBLE PRECISION
         Sum of shifts used in current segment.

DESIG

          DESIG is DOUBLE PRECISION
         Lower order part of SIGMA

QMAX

          QMAX is DOUBLE PRECISION
         Maximum value of q.

NFAIL

          NFAIL is INTEGER
         Increment NFAIL by 1 each time the shift was too big.

ITER

          ITER is INTEGER
         Increment ITER by 1 for each iteration.

NDIV

          NDIV is INTEGER
         Increment NDIV by 1 for each division.

IEEE

          IEEE is LOGICAL
         Flag for IEEE or non IEEE arithmetic (passed to DLASQ5).

TTYPE

          TTYPE is INTEGER
         Shift type.

DMIN1

          DMIN1 is DOUBLE PRECISION

DMIN2

          DMIN2 is DOUBLE PRECISION

          DN is DOUBLE PRECISION

DN1

          DN1 is DOUBLE PRECISION

DN2

          DN2 is DOUBLE PRECISION

          G is DOUBLE PRECISION

TAU

          TAU is DOUBLE PRECISION

         These are passed as arguments in order to save their values
         between calls to DLASQ3.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 179 of file dlasq3.f.

subroutine slasq3 (integer i0, integer n0, real, dimension( * ) z, integer pp, real dmin, real sigma, real desig, real qmax, integer nfail, integer iter, integer ndiv, logical ieee, integer ttype, real dmin1, real dmin2, real dn, real dn1, real dn2, real g, real tau)

SLASQ3 checks for deflation, computes a shift and calls dqds. Used by sbdsqr.