---
name: "laisnan"
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/laisnan"
---

# laisnan(3)

laisnan: test for NaN, unoptimized

## NAME

laisnan - laisnan: test for NaN, unoptimized

## SYNOPSIS

### Functions

logical function **dlaisnan** (din1, din2)\
 **DLAISNAN** tests input for NaN by comparing two arguments for inequality.  logical function **slaisnan** (sin1, sin2)\
 **SLAISNAN** tests input for NaN by comparing two arguments for inequality.

## Detailed Description

## Function Documentation

### logical function dlaisnan (double precision, intent(in) din1, double precision, intent(in) din2)

**DLAISNAN** tests input for NaN by comparing two arguments for inequality.

**Purpose:**

```
!>
!> This routine is not for general use.  It exists solely to avoid
!> over-optimization in DISNAN.
!>
!> DLAISNAN checks for NaNs by comparing its two arguments for
!> inequality.  NaN is the only floating-point value where NaN != NaN
!> returns .TRUE.  To check for NaNs, pass the same variable as both
!> arguments.
!>
!> A compiler must assume that the two arguments are
!> not the same variable, and the test will not be optimized away.
!> Interprocedural or whole-program optimization may delete this
!> test.  The ISNAN functions will be replaced by the correct
!> Fortran 03 intrinsic once the intrinsic is widely available.
!>
```

**Parameters**

*DIN1*

```
!>          DIN1 is DOUBLE PRECISION
!>
```

*DIN2*

```
!>          DIN2 is DOUBLE PRECISION
!>          Two numbers to compare for inequality.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **73** of file **dlaisnan.f**.

### logical function slaisnan (real, intent(in) sin1, real, intent(in) sin2)

**SLAISNAN** tests input for NaN by comparing two arguments for inequality.

**Purpose:**

```
!>
!> This routine is not for general use.  It exists solely to avoid
!> over-optimization in SISNAN.
!>
!> SLAISNAN checks for NaNs by comparing its two arguments for
!> inequality.  NaN is the only floating-point value where NaN != NaN
!> returns .TRUE.  To check for NaNs, pass the same variable as both
!> arguments.
!>
!> A compiler must assume that the two arguments are
!> not the same variable, and the test will not be optimized away.
!> Interprocedural or whole-program optimization may delete this
!> test.  The ISNAN functions will be replaced by the correct
!> Fortran 03 intrinsic once the intrinsic is widely available.
!>
```

**Parameters**

*SIN1*

```
!>          SIN1 is REAL
!>
```

*SIN2*

```
!>          SIN2 is REAL
!>          Two numbers to compare for inequality.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **73** of file **slaisnan.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.