LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ slasq3()

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.

Download SLASQ3 + dependencies [TGZ] [ZIP] [TXT]

Purpose:
!>
!> SLASQ3 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
[in]I0
!>          I0 is INTEGER
!>         First index.
!>
[in,out]N0
!>          N0 is INTEGER
!>         Last index.
!>
[in,out]Z
!>          Z is REAL array, dimension ( 4*N0 )
!>         Z holds the qd array.
!>
[in,out]PP
!>          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.
!>
[out]DMIN
!>          DMIN is REAL
!>         Minimum value of d.
!>
[out]SIGMA
!>          SIGMA is REAL
!>         Sum of shifts used in current segment.
!>
[in,out]DESIG
!>          DESIG is REAL
!>         Lower order part of SIGMA
!>
[in]QMAX
!>          QMAX is REAL
!>         Maximum value of q.
!>
[in,out]NFAIL
!>          NFAIL is INTEGER
!>         Increment NFAIL by 1 each time the shift was too big.
!>
[in,out]ITER
!>          ITER is INTEGER
!>         Increment ITER by 1 for each iteration.
!>
[in,out]NDIV
!>          NDIV is INTEGER
!>         Increment NDIV by 1 for each division.
!>
[in]IEEE
!>          IEEE is LOGICAL
!>         Flag for IEEE or non IEEE arithmetic (passed to SLASQ5).
!>
[in,out]TTYPE
!>          TTYPE is INTEGER
!>         Shift type.
!>
[in,out]DMIN1
!>          DMIN1 is REAL
!>
[in,out]DMIN2
!>          DMIN2 is REAL
!>
[in,out]DN
!>          DN is REAL
!>
[in,out]DN1
!>          DN1 is REAL
!>
[in,out]DN2
!>          DN2 is REAL
!>
[in,out]G
!>          G is REAL
!>
[in,out]TAU
!>          TAU is REAL
!>
!>         These are passed as arguments in order to save their values
!>         between calls to SLASQ3.
!>
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.