NAME¶

SLARRC - 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