LAPACK

NAME¶

lasq3 - lasq3: dqds step

SYNOPSIS¶

Functions¶

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.

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.