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dlarra.f(3)                         LAPACK                         dlarra.f(3)


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
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2                   Sat Nov 16 2013                    dlarra.f(3)

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