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Manual

larra

NAME
SYNOPSIS
Functions
Detailed Description
Function Documentation
subroutine dlarra (integer n, double precision, dimension( * ) d, doubleprecision, dimension( * ) e, double precision, dimension( * ) e2,double precision spltol, double precision tnrm, integer nsplit,integer, dimension( * ) isplit, integer info)
subroutine slarra (integer n, real, dimension( * ) d, real, dimension( * )e, real, dimension( * ) e2, real spltol, real tnrm, integer nsplit,integer, dimension( * ) isplit, integer info)
Author

NAME

larra - larra: step in stemr

SYNOPSIS

Functions

subroutine dlarra (n, d, e, e2, spltol, tnrm, nsplit, isplit, info)
DLARRA computes the splitting points with the specified threshold.
subroutine slarra (n, d, e, e2, spltol, tnrm, nsplit, isplit, info)
SLARRA computes the splitting points with the specified threshold.

Detailed Description

Function Documentation

subroutine dlarra (integer n, double precision, dimension( * ) d, doubleprecision, dimension( * ) e, double precision, dimension( * ) e2,double precision spltol, double precision tnrm, integer nsplit,integer, dimension( * ) isplit, integer info)

DLARRA computes the splitting points with the specified threshold.

Purpose:

Compute the splitting points with threshold SPLTOL.
DLARRA sets any ’small’ off-diagonal elements to zero.

Parameters

N

N is INTEGER
The order of the matrix. N > 0.

D

D is DOUBLE PRECISION array, dimension (N)
On entry, the N diagonal elements of the tridiagonal
matrix T.

E

E is DOUBLE PRECISION 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 DOUBLE PRECISION 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 zero

SPLTOL

SPLTOL is DOUBLE PRECISION
The threshold for splitting. Two criteria can be used:
SPLTOL<0 : criterion based on absolute off-diagonal value
SPLTOL>0 : criterion that preserves relative accuracy

TNRM

TNRM is DOUBLE PRECISION
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

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

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

subroutine slarra (integer n, real, dimension( * ) d, real, dimension( * )e, real, dimension( * ) e2, real spltol, real tnrm, integer nsplit,integer, dimension( * ) isplit, integer info)

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.

Parameters

N

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 zero

SPLTOL

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 accuracy

TNRM

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

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

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

Author

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