SYNOPSIS

SUBROUTINE DLARRC(

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

    

CHARACTER JOBT

    

INTEGER EIGCNT, INFO, LCNT, N, RCNT

    

DOUBLE PRECISION PIVMIN, VL, VU

    

DOUBLE PRECISION 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