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slarra.f(3) | LAPACK | slarra.f(3) |
NAME¶
slarra.f -SYNOPSIS¶
Functions/Subroutines¶
subroutine slarra (N, D, E, E2, SPLTOL, TNRM, NSPLIT, ISPLIT, INFO)
Function/Subroutine Documentation¶
subroutine slarra (integerN, real, dimension( * )D, real, dimension( * )E, real, dimension( * )E2, realSPLTOL, realTNRM, integerNSPLIT, integer, dimension( * )ISPLIT, integerINFO)¶
SLARRA computes the splitting points with the specified threshold. Purpose:Compute the splitting points with threshold SPLTOL. SLARRA sets any "small" off-diagonal elements to zero.
N
Author:
N is INTEGER The order of the matrix. N > 0.D
D is REAL array, dimension (N) On entry, the N diagonal elements of the tridiagonal matrix T.E
E is REAL array, dimension (N) On entry, the first (N-1) 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.E2
E2 is REAL array, dimension (N) On entry, the first (N-1) 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 zeroSPLTOL
SPLTOL is REAL The threshold for splitting. Two criteria can be used: SPLTOL<0 : criterion based on absolute off-diagonal value SPLTOL>0 : criterion that preserves relative accuracyTNRM
TNRM is REAL The norm of the matrix.NSPLIT
NSPLIT is INTEGER The number of blocks T splits into. 1 <= NSPLIT <= N.ISPLIT
ISPLIT 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 NSPLIT-th consists of rows/columns ISPLIT(NSPLIT-1)+1 through ISPLIT(NSPLIT)=N.INFO
INFO is INTEGER = 0: successful exit
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 slarra.f.
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
Author¶
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