Difference between NaN and NA?

[Matthias Brennwald]

Dear all

What is the difference between NaN and NA? I guess there are "different" 
differences, like technical aspects related to the internal programming of 
Octave (or its commercial counterpart), but also related to conventions 
when/how to use NaN or NA.

I tend to not use NA, and use NaN instead in more or less all situations where 
a variable does not contain a true numerical value. I do this mainly because I 
don't now the difference between the two and therefore decided not to mix them. 
However, I suspect it might be useful to use both in a somehow meaningful 
manner. I'd therefore like to know in which situations you'd use NaN rather 
than NA (and vice versa).

Matthias

----
Matthias Brennwald, Käferholzstrasse 173, CH-8046 Zürich, +41 44 364 17 03