NAME¶

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

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