Stable Numerics Subroutine Library
Programming Reference Manual
Version 1.2 DD-00006-012

3.6.1 Not-A-Number Pair

A pair is considered a Not-a-Number (NaN) if either of its components, x or y, is NaN. This aligns with the IEEE 754 standard for floating-point arithmetic, where any operation involving NaN propagates the NaN value. Specifically:

〈x,y⟩= NaN if x =NaN∨ y= NaN.

In such cases, the pair cannot represent a valid numerical value, and any arithmetic operation involving a NaN pair will result in another NaN pair.