Should NaN be reported as "UNDEFINED" ?

[Ethan M. <merritt@u.washington.edu>]

On a machine with IEEE-compliant floating point interpretations,
the string "NaN"  (not case sensitive) is a legal floating point
value.  Thus if NaN occurs in an input data file, the point is 
not flagged as DF_UNDEFINED.

Should it be?  

DF_UNDEFINED usually means some random non-parsable
junk appears in the field, or perhaps the field is empty.

I've uploaded a trivial patch that marks input NaN values as
UNDEFINED, attached to Bug #1490699

But I'd like to hear whether everyone agrees that this is
correct behaviour.

What about infinities ("Inf")?  
I am inclined to pass those through, since the sign information
is still present and conceivably a plotting function would want
to handle +/- Inf explicitly.

-- 
Ethan A Merritt
Biomolecular Structure Center
University of Washington, Seattle WA