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CentOS 7.0 - man page for slaneg (centos section 3)

slaneg.f(3)							      LAPACK							       slaneg.f(3)

slaneg.f -
Functions/Subroutines INTEGER function slaneg (N, D, LLD, SIGMA, PIVMIN, R) SLANEG computes the Sturm count. Function/Subroutine Documentation INTEGER function slaneg (integerN, real, dimension( * )D, real, dimension( * )LLD, realSIGMA, realPIVMIN, integerR) SLANEG computes the Sturm count. Purpose: SLANEG 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 SLARRB. 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, "Benefits of IEEE-754 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. D D is REAL array, dimension (N) The N diagonal elements of the diagonal matrix D. LLD LLD is REAL array, dimension (N-1) The (N-1) elements L(i)*L(i)*D(i). SIGMA SIGMA is REAL Shift amount in T - sigma I = L D L^T. PIVMIN PIVMIN is REAL The minimum pivot in the Sturm sequence. May be used when zero pivots are encountered on non-IEEE-754 architectures. R 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. 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 slaneg.f. Author Generated automatically by Doxygen for LAPACK from the source code. Version 3.4.2 Tue Sep 25 2012 slaneg.f(3)