reference/math/functions/is-nan.xml
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61374bbe228e8e9c55a24aba59a1e2bb2a871148
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<methodparam><type>float</type><parameter>num</parameter></methodparam>
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</methodsynopsis>
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<para>
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Returns whether the given <parameter>num</parameter> is <literal>NAN</literal> (<quote>Not A Number</quote>).
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Returns whether the given <parameter>num</parameter> is <constant>NAN</constant> (<quote>Not A Number</quote>).
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</para>
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<para>
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<literal>NAN</literal> is returned from mathematical operations that are undefined,
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<constant>NAN</constant> is returned from mathematical operations that are undefined,
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for example when passing parameters outside of function’s input domain. The square root
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(<function>sqrt</function>) is only defined for positive numbers, passing a negative number
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will result in <literal>NAN</literal>. Other examples of operations returning <literal>NAN</literal>
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are dividing <literal>INF</literal> by <literal>INF</literal> and any operation involving an
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existing <literal>NAN</literal> value.
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will result in <constant>NAN</constant>. Other examples of operations returning <constant>NAN</constant>
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are dividing <constant>INF</constant> by <constant>INF</constant> and any operation involving an
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existing <constant>NAN</constant> value.
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</para>
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<note>
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<para>
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Despite its name of <quote>Not A Number</quote>, <literal>NAN</literal> is a valid value of type &float;.
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Despite its name of <quote>Not A Number</quote>, <constant>NAN</constant> is a valid value of type &float;.
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</para>
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</note>
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<caution>
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<para>
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<literal>NAN</literal> does not compare equal to <literal>NAN</literal>. To check whether
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a float is <literal>NAN</literal>, <function>is_nan</function> must be used. Checking
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<constant>NAN</constant> does not compare equal to <constant>NAN</constant>. To check whether
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a float is <constant>NAN</constant>, <function>is_nan</function> must be used. Checking
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<code>$float === NAN</code> will not work.
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</para>
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</caution>
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<refsect1 role="returnvalues">
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&reftitle.returnvalues;
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<para>
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&true; if <parameter>num</parameter> is <literal>NAN</literal>, else &false;.
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&true; if <parameter>num</parameter> is <constant>NAN</constant>, else &false;.
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</para>
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</refsect1>
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