SLARRJ (3)  Linux Manuals
NAME
slarrj.f 
SYNOPSIS
Functions/Subroutines
subroutine slarrj (N, D, E2, IFIRST, ILAST, RTOL, OFFSET, W, WERR, WORK, IWORK, PIVMIN, SPDIAM, INFO)
SLARRJ performs refinement of the initial estimates of the eigenvalues of the matrix T.
Function/Subroutine Documentation
subroutine slarrj (integerN, real, dimension( * )D, real, dimension( * )E2, integerIFIRST, integerILAST, realRTOL, integerOFFSET, real, dimension( * )W, real, dimension( * )WERR, real, dimension( * )WORK, integer, dimension( * )IWORK, realPIVMIN, realSPDIAM, integerINFO)
SLARRJ performs refinement of the initial estimates of the eigenvalues of the matrix T.
Purpose:

Given the initial eigenvalue approximations of T, SLARRJ does bisection to refine the eigenvalues of T, W( IFIRSTOFFSET ) through W( ILASTOFFSET ), to more accuracy. Initial guesses for these eigenvalues are input in W, the corresponding estimate of the error in these guesses in WERR. During bisection, intervals [left, right] are maintained by storing their midpoints and semiwidths in the arrays W and WERR respectively.
Parameters:

N
N is INTEGER The order of the matrix.
DD is REAL array, dimension (N) The N diagonal elements of T.
E2E2 is REAL array, dimension (N1) The Squares of the (N1) subdiagonal elements of T.
IFIRSTIFIRST is INTEGER The index of the first eigenvalue to be computed.
ILASTILAST is INTEGER The index of the last eigenvalue to be computed.
RTOLRTOL is REAL Tolerance for the convergence of the bisection intervals. An interval [LEFT,RIGHT] has converged if RIGHTLEFT.LT.RTOL*MAX(LEFT,RIGHT).
OFFSETOFFSET is INTEGER Offset for the arrays W and WERR, i.e., the IFIRSTOFFSET through ILASTOFFSET elements of these arrays are to be used.
WW is REAL array, dimension (N) On input, W( IFIRSTOFFSET ) through W( ILASTOFFSET ) are estimates of the eigenvalues of L D L^T indexed IFIRST through ILAST. On output, these estimates are refined.
WERRWERR is REAL array, dimension (N) On input, WERR( IFIRSTOFFSET ) through WERR( ILASTOFFSET ) are the errors in the estimates of the corresponding elements in W. On output, these errors are refined.
WORKWORK is REAL array, dimension (2*N) Workspace.
IWORKIWORK is INTEGER array, dimension (2*N) Workspace.
PIVMINPIVMIN is REAL The minimum pivot in the Sturm sequence for T.
SPDIAMSPDIAM is REAL The spectral diameter of T.
INFOINFO is INTEGER Error flag.
Author:

Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
 September 2012
Contributors:

Beresford Parlett, University of California, Berkeley, USA
Jim Demmel, University of California, Berkeley, USA
Inderjit Dhillon, University of Texas, Austin, USA
Osni Marques, LBNL/NERSC, USA
Christof Voemel, University of California, Berkeley, USA
Definition at line 167 of file slarrj.f.
Author
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