DLANEG (3)  Linux Manuals
NAME
dlaneg.f 
SYNOPSIS
Functions/Subroutines
INTEGER function dlaneg (N, D, LLD, SIGMA, PIVMIN, R)
DLANEG computes the Sturm count.
Function/Subroutine Documentation
INTEGER function dlaneg (integerN, double precision, dimension( * )D, double precision, dimension( * )LLD, double precisionSIGMA, double precisionPIVMIN, integerR)
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 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.)
Parameters:

N
N is INTEGER The order of the matrix.
DD is DOUBLE PRECISION array, dimension (N) The N diagonal elements of the diagonal matrix D.
LLDLLD is DOUBLE PRECISION array, dimension (N1) The (N1) elements L(i)*L(i)*D(i).
SIGMASIGMA is DOUBLE PRECISION Shift amount in T  sigma I = L D L^T.
PIVMINPIVMIN is DOUBLE PRECISION The minimum pivot in the Sturm sequence. May be used when zero pivots are encountered on nonIEEE754 architectures.
RR 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.
Date:
 September 2012
Contributors:

Osni Marques, LBNL/NERSC, USA
Christof Voemel, University of California, Berkeley, USA
Jason Riedy, University of California, Berkeley, USA
Definition at line 119 of file dlaneg.f.
Author
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