SLARRK (3)  Linux Manuals
NAME
slarrk.f 
SYNOPSIS
Functions/Subroutines
subroutine slarrk (N, IW, GL, GU, D, E2, PIVMIN, RELTOL, W, WERR, INFO)
SLARRK computes one eigenvalue of a symmetric tridiagonal matrix T to suitable accuracy.
Function/Subroutine Documentation
subroutine slarrk (integerN, integerIW, realGL, realGU, real, dimension( * )D, real, dimension( * )E2, realPIVMIN, realRELTOL, realW, realWERR, integerINFO)
SLARRK computes one eigenvalue of a symmetric tridiagonal matrix T to suitable accuracy.
Purpose:

SLARRK computes one eigenvalue of a symmetric tridiagonal matrix T to suitable accuracy. This is an auxiliary code to be called from SSTEMR. To avoid overflow, the matrix must be scaled so that its largest element is no greater than overflow**(1/2) * underflow**(1/4) in absolute value, and for greatest accuracy, it should not be much smaller than that. See W. Kahan "Accurate Eigenvalues of a Symmetric Tridiagonal Matrix", Report CS41, Computer Science Dept., Stanford University, July 21, 1966.
Parameters:

N
N is INTEGER The order of the tridiagonal matrix T. N >= 0.
IWIW is INTEGER The index of the eigenvalues to be returned.
GLGL is REAL
GUGU is REAL An upper and a lower bound on the eigenvalue.
DD is REAL array, dimension (N) The n diagonal elements of the tridiagonal matrix T.
E2E2 is REAL array, dimension (N1) The (n1) squared offdiagonal elements of the tridiagonal matrix T.
PIVMINPIVMIN is REAL The minimum pivot allowed in the Sturm sequence for T.
RELTOLRELTOL is REAL The minimum relative width of an interval. When an interval is narrower than RELTOL times the larger (in magnitude) endpoint, then it is considered to be sufficiently small, i.e., converged. Note: this should always be at least radix*machine epsilon.
WW is REAL
WERRWERR is REAL The error bound on the corresponding eigenvalue approximation in W.
INFOINFO is INTEGER = 0: Eigenvalue converged = 1: Eigenvalue did NOT converge
Internal Parameters:

FUDGE REAL , default = 2 A "fudge factor" to widen the Gershgorin intervals.
Author:

Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
 September 2012
Definition at line 145 of file slarrk.f.
Author
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