DLARRA (3)  Linux Manuals
NAME
dlarra.f 
SYNOPSIS
Functions/Subroutines
subroutine dlarra (N, D, E, E2, SPLTOL, TNRM, NSPLIT, ISPLIT, INFO)
DLARRA computes the splitting points with the specified threshold.
Function/Subroutine Documentation
subroutine dlarra (integerN, double precision, dimension( * )D, double precision, dimension( * )E, double precision, dimension( * )E2, double precisionSPLTOL, double precisionTNRM, integerNSPLIT, integer, dimension( * )ISPLIT, integerINFO)
DLARRA computes the splitting points with the specified threshold.
Purpose:

Compute the splitting points with threshold SPLTOL. DLARRA sets any "small" offdiagonal elements to zero.
Parameters:

N
N is INTEGER The order of the matrix. N > 0.
DD is DOUBLE PRECISION array, dimension (N) On entry, the N diagonal elements of the tridiagonal matrix T.
EE is DOUBLE PRECISION array, dimension (N) On entry, the first (N1) entries contain the subdiagonal elements of the tridiagonal matrix T; E(N) need not be set. On exit, the entries E( ISPLIT( I ) ), 1 <= I <= NSPLIT, are set to zero, the other entries of E are untouched.
E2E2 is DOUBLE PRECISION array, dimension (N) On entry, the first (N1) entries contain the SQUARES of the subdiagonal elements of the tridiagonal matrix T; E2(N) need not be set. On exit, the entries E2( ISPLIT( I ) ), 1 <= I <= NSPLIT, have been set to zero
SPLTOLSPLTOL is DOUBLE PRECISION The threshold for splitting. Two criteria can be used: SPLTOL<0 : criterion based on absolute offdiagonal value SPLTOL>0 : criterion that preserves relative accuracy
TNRMTNRM is DOUBLE PRECISION The norm of the matrix.
NSPLITNSPLIT is INTEGER The number of blocks T splits into. 1 <= NSPLIT <= N.
ISPLITISPLIT is INTEGER array, dimension (N) The splitting points, at which T breaks up into blocks. The first block consists of rows/columns 1 to ISPLIT(1), the second of rows/columns ISPLIT(1)+1 through ISPLIT(2), etc., and the NSPLITth consists of rows/columns ISPLIT(NSPLIT1)+1 through ISPLIT(NSPLIT)=N.
INFOINFO is INTEGER = 0: successful exit
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 136 of file dlarra.f.
Author
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