| NAN | Constant (Pseudo-constant)

math.h, timath.h

A constant defining an undefined value.

`NAN` is an acronyme of "Not a Number". TIOS generates `NAN` when nothing can be deduced about the magnitude of the result (for example, when dividing zero by zero, or when substracting two infinities of the same sign). Also, TIOS generates `NAN` when the argument of a function is out of legal range, excluding values of the argument which produces infinity results. For example, log will produce `NAN` when the argument is negative, but when the argument is zero, the result is NEGATIVE_INF.
`NAN` also belongs to the class of "transfinite" numbers (see is_transfinite). Use is_nan to check whether a value is `NAN`. This is a common method to check in run time whether the arguments of the called math functions was legal.

See also: UNSIGNED_INF