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" 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.

       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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