Obtain Nan or Determine if a Value is Nan

@(@\newcommand{\W}[1]{ \; #1 \; } \newcommand{\R}[1]{ {\rm #1} } \newcommand{\B}[1]{ {\bf #1} } \newcommand{\D}[2]{ \frac{\partial #1}{\partial #2} } \newcommand{\DD}[3]{ \frac{\partial^2 #1}{\partial #2 \partial #3} } \newcommand{\Dpow}[2]{ \frac{\partial^{#1}}{\partial {#2}^{#1}} } \newcommand{\dpow}[2]{ \frac{ {\rm d}^{#1}}{{\rm d}\, {#2}^{#1}} }@)@This is cppad-20221105 documentation. Here is a link to its current documentation . Obtain Nan or Determine if a Value is Nan
Syntax

# include <cppad/utility/nan.hpp>

b = isnan(s)

b = hasnan(v)

Purpose
It obtain and check for the value not a number nan. The IEEE standard specifies that a floating point value a is nan if and only if the following returns true



    a != a

Include
The file cppad/utility/nan.hpp is included by cppad/cppad.hpp but it can also be included separately with out the rest of the CppAD routines.

Macros
Some C++ compilers use preprocessor symbols called nan and isnan. These preprocessor symbols will no longer be defined after this file is included.

isnan
This routine determines if a scalar value is nan.

s
The argument s has prototype



    const Scalar s

b
The return value b has prototype



    bool b

It is true if the value s is nan.

hasnan
This routine determines if a SimpleVector has an element that is nan.

v
The argument v has prototype



    const Vector &v

(see Vector for the definition of Vector ).

b
The return value b has prototype



    bool b

It is true if the vector v has a nan.

nan(zero)

Deprecated 2015-10-04
This routine has been deprecated, use CppAD numeric limits quiet_NaN in its place.

Syntax

s = nan(z)

z
The argument z has prototype



    const Scalar &z

and its value is zero (see Scalar for the definition of Scalar ).

s
The return value s has prototype



    Scalar s

It is the value nan for this floating point type.

Scalar
The type Scalar must support the following operations;

Operation	Description
`a / b`	division operator (returns a `Scalar` object)
`a == b`	equality operator (returns a `bool` object)
`a != b`	not equality operator (returns a `bool` object)

Note that the division operator will be used with a and b equal to zero. For some types (e.g. int) this may generate an exception. No attempt is made to catch any such exception.

Vector
The type Vector must be a SimpleVector class with elements of type Scalar .

Example
The file nan.cpp contains an example and test of this routine.

Input File: include/cppad/utility/nan.hpp