Provided by: liblapack-doc_3.12.0-3build1.1_all 
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, double precision, 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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