# dlarrr (l) - Linux Manuals

## dlarrr: tests to decide whether the symmetric tridiagonal matrix T warrants expensive computations which guarantee high relative accuracy in the eigenvalues

## 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 byBeresford 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