---
name: "sstect"
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/sstect.f"
---

# sstect(3)

Part of [sstect.f(3)](/sstect.f/3.md).

## NAME

TESTING/EIG/sstect.f

## SYNOPSIS

### Functions/Subroutines

subroutine **sstect** (n, a, b, shift, num)\
 **SSTECT**

## Function/Subroutine Documentation

### subroutine sstect (integer n, real, dimension( \* ) a, real, dimension( \* ) b, real shift, integer num)

**SSTECT**

**Purpose:**

```
!>
!>    SSTECT counts the number NUM of eigenvalues of a tridiagonal
!>    matrix T which are less than or equal to SHIFT. T has
!>    diagonal entries A(1), ... , A(N), and offdiagonal entries
!>    B(1), ..., B(N-1).
!>    See W. Kahan , Report CS41, Computer Science Dept., Stanford
!>    University, July 21, 1966
!>
```

**Parameters**

*N*

```
!>          N is INTEGER
!>          The dimension of the tridiagonal matrix T.
!>
```

*A*

```
!>          A is REAL array, dimension (N)
!>          The diagonal entries of the tridiagonal matrix T.
!>
```

*B*

```
!>          B is REAL array, dimension (N-1)
!>          The offdiagonal entries of the tridiagonal matrix T.
!>
```

*SHIFT*

```
!>          SHIFT is REAL
!>          The shift, used as described under Purpose.
!>
```

*NUM*

```
!>          NUM is INTEGER
!>          The number of eigenvalues of T less than or equal
!>          to SHIFT.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **81** of file **sstect.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.