---
name: "dslect.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/dslect.f"
---

# dslect.f(3)

## NAME

TESTING/EIG/dslect.f

## SYNOPSIS

### Functions/Subroutines

logical function **dslect** (zr, zi)\
 **DSLECT**

## Function/Subroutine Documentation

### logical function dslect (double precision zr, double precision zi)

**DSLECT**

**Purpose:**

```
!>
!> DSLECT returns .TRUE. if the eigenvalue ZR+sqrt(-1)*ZI is to be
!> selected, and otherwise it returns .FALSE.
!> It is used by DCHK41 to test if DGEES successfully sorts eigenvalues,
!> and by DCHK43 to test if DGEESX successfully sorts eigenvalues.
!>
!> The common block /SSLCT/ controls how eigenvalues are selected.
!> If SELOPT = 0, then DSLECT return .TRUE. when ZR is less than zero,
!> and .FALSE. otherwise.
!> If SELOPT is at least 1, DSLECT returns SELVAL(SELOPT) and adds 1
!> to SELOPT, cycling back to 1 at SELMAX.
!>
```

**Parameters**

*ZR*

```
!>          ZR is DOUBLE PRECISION
!>          The real part of a complex eigenvalue ZR + i*ZI.
!>
```

*ZI*

```
!>          ZI is DOUBLE PRECISION
!>          The imaginary part of a complex eigenvalue ZR + i*ZI.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **61** of file **dslect.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.