Library Functions Manual

NAME¶

laneg - laneg: Sturm count

SYNOPSIS¶

Functions¶

integer function DLANEG (n, d, lld, sigma, pivmin, r)
DLANEG computes the Sturm count. integer function SLANEG (n, d, lld, sigma, pivmin, r)
SLANEG computes the Sturm count.

Detailed Description¶

Function Documentation¶

integer function DLANEG (integer n, double precision, dimension( * ) d, double precision, dimension( * ) lld, double precision sigma, double precision pivmin, integer r)¶

DLANEG computes the Sturm count.

Purpose:

!>
!> DLANEG computes the Sturm count, the number of negative pivots
!> encountered while factoring tridiagonal T - sigma I = L D L^T.
!> This implementation works directly on the factors without forming
!> the tridiagonal matrix T.  The Sturm count is also the number of
!> eigenvalues of T less than sigma.
!>
!> This routine is called from DLARRB.
!>
!> The current routine does not use the PIVMIN parameter but rather
!> requires IEEE-754 propagation of Infinities and NaNs.  This
!> routine also has no input range restrictions but does require
!> default exception handling such that x/0 produces Inf when x is
!> non-zero, and Inf/Inf produces NaN.  For more information, see:
!>
!>   Marques, Riedy, and Voemel,  SIAM Journal on
!>   Scientific Computing, v28, n5, 2006.  DOI 10.1137/050641624
!>   (Tech report version in LAWN 172 with the same title.)
!>

Parameters

!>          N is INTEGER
!>          The order of the matrix.
!>

!>          D is DOUBLE PRECISION array, dimension (N)
!>          The N diagonal elements of the diagonal matrix D.
!>

LLD

!>          LLD is DOUBLE PRECISION array, dimension (N-1)
!>          The (N-1) elements L(i)*L(i)*D(i).
!>

SIGMA

!>          SIGMA is DOUBLE PRECISION
!>          Shift amount in T - sigma I = L D L^T.
!>

PIVMIN

!>          PIVMIN is DOUBLE PRECISION
!>          The minimum pivot in the Sturm sequence.  May be used
!>          when zero pivots are encountered on non-IEEE-754
!>          architectures.
!>

!>          R is INTEGER
!>          The twist index for the twisted factorization that is used
!>          for the negcount.
!>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Contributors:

Osni Marques, LBNL/NERSC, USA
Christof Voemel, University of California, Berkeley, USA
Jason Riedy, University of California, Berkeley, USA

Definition at line 117 of file dlaneg.f.

integer function SLANEG (integer n, real, dimension( * ) d, real, dimension( * ) lld, real sigma, real pivmin, integer r)¶

SLANEG computes the Sturm count.