# larrr - Man Page

larrr: step in stemr, test to do expensive tridiag eig algorithm

## Synopsis

### Functions

subroutine **dlarrr** (n, d, e, info)**DLARRR** performs tests to decide whether the symmetric tridiagonal matrix T warrants expensive computations which guarantee high relative accuracy in the eigenvalues.

subroutine **slarrr** (n, d, e, info)**SLARRR** performs tests to decide whether the symmetric tridiagonal matrix T warrants expensive computations which guarantee high relative accuracy in the eigenvalues.

## Detailed Description

## Function Documentation

### subroutine dlarrr (integer n, double precision, dimension( * ) d, double precision, dimension( * ) e, integer info)

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

**Purpose:**

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

**Parameters***N*N is INTEGER The order of the matrix. N > 0.

*D*D is DOUBLE PRECISION array, dimension (N) The N diagonal elements of the tridiagonal matrix T.

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

**Author**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Contributors:**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

Definition at line **93** of file **dlarrr.f**.

### subroutine slarrr (integer n, real, dimension( * ) d, real, dimension( * ) e, integer info)

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

**Purpose:**

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

**Parameters***N*N is INTEGER The order of the matrix. N > 0.

*D*D is REAL array, dimension (N) The N diagonal elements of the tridiagonal matrix T.

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

**Author**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Contributors:**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

Definition at line **93** of file **slarrr.f**.

## Author

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