dlaneg (l)  Linux Manuals
dlaneg: computes the Sturm count, the number of negative pivots encountered while factoring tridiagonal T  sigma I = L D L^T
Command to display dlaneg
manual in Linux: $ man l dlaneg
NAME
DLANEG  computes the Sturm count, the number of negative pivots encountered while factoring tridiagonal T  sigma I = L D L^T
SYNOPSIS
 FUNCTION DLANEG(

N, D, LLD, SIGMA, PIVMIN, R )

IMPLICIT
NONE

INTEGER
DLANEG

INTEGER
N, R

DOUBLE
PRECISION PIVMIN, SIGMA

DOUBLE
PRECISION D( * ), LLD( * )
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 IEEE754 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
nonzero, and Inf/Inf produces NaN. For more information, see:
Marques, Riedy, and Voemel, "Benefits of IEEE754 Features in
Modern Symmetric Tridiagonal Eigensolvers," SIAM Journal on
Scientific Computing, v28, n5, 2006. DOI 10.1137/050641624
(Tech report version in LAWN 172 with the same title.)
ARGUMENTS
 N (input) INTEGER

The order of the matrix.
 D (input) DOUBLE PRECISION array, dimension (N)

The N diagonal elements of the diagonal matrix D.
 LLD (input) DOUBLE PRECISION array, dimension (N1)

The (N1) elements L(i)*L(i)*D(i).
 SIGMA (input) DOUBLE PRECISION

Shift amount in T  sigma I = L D L^T.
 PIVMIN (input) DOUBLE PRECISION

The minimum pivot in the Sturm sequence. May be used
when zero pivots are encountered on nonIEEE754
architectures.
 R (input) INTEGER

The twist index for the twisted factorization that is used
for the negcount.
FURTHER DETAILS
Based on contributions by
Osni Marques, LBNL/NERSC, USA
Christof Voemel, University of California, Berkeley, USA
Jason Riedy, University of California, Berkeley, USA
Pages related to dlaneg
 dlaneg (3)
 dlangb (l)  returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of an n by n band matrix A, with kl subdiagonals and ku superdiagonals
 dlange (l)  returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real matrix A
 dlangt (l)  returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real tridiagonal matrix A
 dlanhs (l)  returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a Hessenberg matrix A
 dlansb (l)  returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of an n by n symmetric band matrix A, with k superdiagonals
 dlansf (l)  returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real symmetric matrix A in RFP format
 dlansp (l)  returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real symmetric matrix A, supplied in packed form
 dlanst (l)  returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real symmetric tridiagonal matrix A
 dlansy (l)  returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real symmetric matrix A