# ?larrc

Computes the number of eigenvalues of the symmetric tridiagonal matrix.

## Syntax

call slarrc( jobt, n, vl, vu, d, e, pivmin, eigcnt, lcnt, rcnt, info )

call dlarrc( jobt, n, vl, vu, d, e, pivmin, eigcnt, lcnt, rcnt, info )

## Description

This routine finds the number of eigenvalues of the symmetric tridiagonal matrix T or of its factorization `L*D*LT` in the specified interval.

## Input Parameters

jobt

  CHARACTER*1.

  `= 'T'`: computes Sturm count for matrix T.

  `= 'L'`: computes Sturm count for matrix `L*D*LT`.

n

  INTEGER.

  The order of the matrix. (`n > 1`).

vl,vu

  REAL for slarrc

  DOUBLE PRECISION for dlarrc

  The lower and upper bounds for the eigenvalues.
d

  REAL for slarrc

  DOUBLE PRECISION for dlarrc

  Array, DIMENSION (n).

  If `jobt= 'T'`: contains the n diagonal elements of the tridiagonal matrix T.

  If `jobt= 'L'`: contains the n diagonal elements of the diagonal matrix D.

e

  REAL for slarrc

  DOUBLE PRECISION for dlarrc

  Array, DIMENSION (n).

  If `jobt= 'T'`: contains the `(n-1)`offdiagonal elements of the matrix T.

  If `jobt= 'L'`: contains the `(n-1)`offdiagonal elements of the matrix L.

pivmin

  REAL for slarrc

  DOUBLE PRECISION for dlarrc

  The minimum pivot in the Sturm sequence for the matrix T.

## Output Parameters

eigcnt
  INTEGER.

  The number of eigenvalues of the symmetric tridiagonal matrix T that are in the half-open interval `(vl,vu]`.

lcnt,rcnt

  INTEGER.

  The left and right negcounts of the interval.

info

  INTEGER.

  Now it is not used and always is set to 0.

Parent topic: Auxiliary Routines