SYNOPSIS

SUBROUTINE DLARRR(

N, D, E, INFO )

    

INTEGER N, INFO

    

DOUBLE PRECISION D( * ), E( * )

PURPOSE

Perform tests to decide whether the symmetric tridiagonal matrix T warrants expensive computations which guarantee high relative accuracy in the eigenvalues.

ARGUMENTS

N (input) INTEGER

The order of the matrix. N > 0.

D (input) DOUBLE PRECISION array, dimension (N)

The N diagonal elements of the tridiagonal matrix T.

E (input/output) DOUBLE PRECISION array, dimension (N)

On entry, the first (N-1) entries contain the subdiagonal elements of the tridiagonal matrix T; E(N) is set to ZERO.

INFO (output) INTEGER

INFO = 0(default) : the matrix warrants computations preserving relative accuracy. INFO = 1 : the matrix warrants computations guaranteeing only absolute accuracy.

FURTHER DETAILS

Based on contributions by

   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