
dlarrk.f(3) LAPACK dlarrk.f(3)
NAME
dlarrk.f 
SYNOPSIS
Functions/Subroutines
subroutine dlarrk (N, IW, GL, GU, D, E2, PIVMIN, RELTOL, W, WERR, INFO)
DLARRK computes one eigenvalue of a symmetric tridiagonal matrix T to suitable
accuracy.
Function/Subroutine Documentation
subroutine dlarrk (integerN, integerIW, double precisionGL, double precisionGU, double
precision, dimension( * )D, double precision, dimension( * )E2, double precisionPIVMIN,
double precisionRELTOL, double precisionW, double precisionWERR, integerINFO)
DLARRK computes one eigenvalue of a symmetric tridiagonal matrix T to suitable accuracy.
Purpose:
DLARRK computes one eigenvalue of a symmetric tridiagonal
matrix T to suitable accuracy. This is an auxiliary code to be
called from DSTEMR.
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.
IW
IW is INTEGER
The index of the eigenvalues to be returned.
GL
GL is DOUBLE PRECISION
GU
GU is DOUBLE PRECISION
An upper and a lower bound on the eigenvalue.
D
D is DOUBLE PRECISION array, dimension (N)
The n diagonal elements of the tridiagonal matrix T.
E2
E2 is DOUBLE PRECISION array, dimension (N1)
The (n1) squared offdiagonal elements of the tridiagonal matrix T.
PIVMIN
PIVMIN is DOUBLE PRECISION
The minimum pivot allowed in the Sturm sequence for T.
RELTOL
RELTOL is DOUBLE PRECISION
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.
W
W is DOUBLE PRECISION
WERR
WERR is DOUBLE PRECISION
The error bound on the corresponding eigenvalue approximation
in W.
INFO
INFO is INTEGER
= 0: Eigenvalue converged
= 1: Eigenvalue did NOT converge
Internal Parameters:
FUDGE DOUBLE PRECISION, 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 dlarrk.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dlarrk.f(3) 
