---
name: "slarrr"
section: "3lapack"
platform: "linux"
package: "liblapack-doc"
version: "3.2.1-8"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/slarrr/3lapack"
---

# slarrr(3lapack)

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

## NAME

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

## SYNOPSIS

- SUBROUTINE SLARRR(

  N, D, E, INFO )

- INTEGER

  N, INFO

- REAL

  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) REAL array, dimension (N)

  The N diagonal elements of the tridiagonal matrix T.

- E (input/output) REAL 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