Re: NaNs not propagating

[sfeam <sf...@us...>]

On Monday, 03 November 2014 06:45:48 PM pl...@pi... wrote:
> Hi,
> 
> I seem have a problem with NaN not propagating to function calls.
> 
> 
> gnuplot>
> 
>   integ(x)=(int_last==0)?(NaN,int_last=x):(int_last=int_last+x)
> 
> plot int_last=0, "-" u 1:(integ($2-44)) w l
> input data ('e' ends) > 1 1
> input data ('e' ends) > 2 2
> input data ('e' ends) > 3 NaN
> input data ('e' ends) > 4 4
> input data ('e' ends) > 5 5
> input data ('e' ends) > e
> 
> gnuplot> print int_last+NaN
> NaN
> 
> 
> This gives a straight line with a break which means that the third line 
> is evaluating NaN as zero and passing -44 to the function.
> 
> I was expecting the argument (NaN-44) to pass NaN to the function which 
> would in turn return and assign a NaN  leaving all further points 
> unplotted.
> 
> Bug or feature ?

I think it rates as a bug.

When the data is read in, a using spec that evaluates to NaN is
flagged as "undefined".  This is sufficient for the purpose of
plotting that one point, but as you have discovered it doesn't
address side-effects of the evaluation.  Arguably if the point
itself is undefined then it is reasonable to say that any 
side-effects are also undefined, but it's less of a surprise
if this makes the side-effect expressions evaluate to NaN also.

I'll whip up a fix for 5.0 and 5.1.



By the way, in the definition you show for function integ()
  integ(x)=(int_last==0)?(NaN,int_last=x):(int_last=int_last+x)
the NaN has no effect whatsover because it is on the left
side of a comma.  That means the function reduces to

  integ(x) = (int_last = int_last+x)

	Ethan