---
name: "dlarrc.f"
section: "3"
platform: "linux"
package: "lapack-doc"
version: "3.12.1-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/dlarrc.f"
---

# dlarrc.f(3)

## NAME

SRC/dlarrc.f

## SYNOPSIS

### Functions/Subroutines

subroutine **dlarrc** (jobt, n, vl, vu, d, e, pivmin, eigcnt, lcnt, rcnt, info)\
 **DLARRC** computes the number of eigenvalues of the symmetric tridiagonal matrix.

## Function/Subroutine Documentation

### subroutine dlarrc (character jobt, integer n, double precision vl, double precision vu, double precision, dimension( \* ) d, double precision, dimension( \* ) e, double precision pivmin, integer eigcnt, integer lcnt, integer rcnt, integer info)

**DLARRC** computes the number of eigenvalues of the symmetric tridiagonal matrix.

**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'.
!>
```

**Parameters**

*JOBT*

```
!>          JOBT is CHARACTER*1
!>          = 'T':  Compute Sturm count for matrix T.
!>          = 'L':  Compute Sturm count for matrix L D L^T.
!>
```

*N*

```
!>          N is INTEGER
!>          The order of the matrix. N > 0.
!>
```

*VL*

```
!>          VL is DOUBLE PRECISION
!>          The lower bound for the eigenvalues.
!>
```

*VU*

```
!>          VU is DOUBLE PRECISION
!>          The upper bound for the eigenvalues.
!>
```

*D*

```
!>          D is 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*

```
!>          E is 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*

```
!>          PIVMIN is DOUBLE PRECISION
!>          The minimum pivot in the Sturm sequence for T.
!>
```

*EIGCNT*

```
!>          EIGCNT is INTEGER
!>          The number of eigenvalues of the symmetric tridiagonal matrix T
!>          that are in the interval (VL,VU]
!>
```

*LCNT*

```
!>          LCNT is INTEGER
!>
```

*RCNT*

```
!>          RCNT is INTEGER
!>          The left and right negcounts of the interval.
!>
```

*INFO*

```
!>          INFO is INTEGER
!>
```

**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 **135** of file **dlarrc.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.