SRC/dlarra.f(3)            Library Functions Manual            SRC/dlarra.f(3)

NAME
       SRC/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 (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  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

       Definition at line 134 of file dlarra.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

LAPACK                          Version 3.12.0                 SRC/dlarra.f(3)