Re: multiple plot lines with plot '-'

[Ethan A M. <sf...@us...>]

On Wednesday, May 16, 2012 12:41:08 pm pl...@pi... wrote:
> On 05/16/12 18:35, Daniel J Sebald wrote:
> > However, this isn't as different as you think.  I would guess that if
> > "datafile" were changed at an instant between when gnuplot does the two
> > plots, the two plots would look different.  The analogy is typing the
> > same thing at the keyboard or pipe when using '-'.
>
> This is not so hypothetical and improbably as it may seem.
> 
> Some of my embedded plots take 16-20s to run the ARM hardware I'm using. 
> It is totally possible (maybe probable) that the source file could 
> change in that time.

That is exactly why I added the "volatile" keyword and the option to
use "refresh" rather than "replot".

The original gnuplot behavior was to always read the file again when
replotting.  If the contents of the file had changed, you got a different
plot.   "volatile" and "refresh" tell it to try to replot using the input
data that was stored internally during the original read, so even if the
file contents have changed you get the same plot.

> plot datafile using 1:2 , '' using 1:3
> 
> Now both these lines are coming out on the same plot , I would expect it 
> to be a snapshot of the data at the same point in time. We are almost 
> certainly going to be comparing them. Currently there is a possibility 
> that the two lines represent different states of the data set.  If they 
> were not coincident in time it could lead to misrepresentation or 
> misinterpretation.

True. There is currently no protection against that, although there may
be ways of capturing all the needed information in a single plot clause.
E.g.
   plot datafile using 1:2:3 with yerrorbars pt 0
If this is a serious concern, it would help to have an example of the
real-world plot that is desired.