# ?larrr

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

## Syntax

call slarrr( n, d, e, info )

call dlarrr( n, d, e, info )

## Description

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

## Input Parameters

n

  INTEGER. The order of the matrix T. (`n > 0`).

d

  REAL for slarrr

  DOUBLE PRECISION for dlarrr

  Array, DIMENSION (n).

  Contains n diagonal elements of the matrix T.

e

  REAL for slarrr

  DOUBLE PRECISION for dlarrr

  Array, DIMENSION (`n`).

  The first `(n-1)` entries contain sub-diagonal elements of the tridiagonal matrix T; `e(n)` is set to 0.

## Output Parameters

info

  INTEGER.

  `= 0:` the matrix warrants computations preserving relative accuracy (default value).

  `= -1:` the matrix warrants computations guaranteeing only absolute accuracy.

Parent topic: Auxiliary Routines