 SLARRC(3) the number of eigenvalues of the symmetric tridiagonal matrix T that are in the interval (VL,VU] if JOBT = 'T', and of L D L^T if JOBT = 'L'

## SYNOPSIS

SUBROUTINE SLARRC(
JOBT, N, VL, VU, D, E, PIVMIN, EIGCNT, LCNT, RCNT, INFO )

CHARACTER JOBT

INTEGER EIGCNT, INFO, LCNT, N, RCNT

REAL PIVMIN, VL, VU

REAL D( * ), E( * )

## PURPOSE

Find the number of eigenvalues of the symmetric tridiagonal matrix T that are in the interval (VL,VU] if JOBT = 'T', and of L D L^T if JOBT = 'L'.

## ARGUMENTS

JOBT (input) CHARACTER*1
= 'T': Compute Sturm count for matrix T.
= 'L': Compute Sturm count for matrix L D L^T.
N (input) INTEGER
The order of the matrix. N > 0.
VL (input) DOUBLE PRECISION
VU (input) DOUBLE PRECISION The lower and upper bounds for the eigenvalues.
D (input) DOUBLE PRECISION array, dimension (N)
JOBT = 'T': The N diagonal elements of the tridiagonal matrix T.
JOBT = 'L': The N diagonal elements of the diagonal matrix D.
E (input) DOUBLE PRECISION array, dimension (N)

JOBT = 'T': The N-1 offdiagonal elements of the matrix T.
JOBT = 'L': The N-1 offdiagonal elements of the matrix L.
PIVMIN (input) DOUBLE PRECISION
The minimum pivot in the Sturm sequence for T.
EIGCNT (output) INTEGER
The number of eigenvalues of the symmetric tridiagonal matrix T that are in the interval (VL,VU]
LCNT (output) INTEGER
RCNT (output) INTEGER The left and right negcounts of the interval.
INFO (output) INTEGER

## 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