Re: [Gnuplot-info] extrapolation beyond input range?

[swlab <sw...@co...>]

On Tuesday 08 February 2005 16:29, Dan Jacobson wrote:
> I wanted a way to get gnuplot to 'keep drawing those great lines,
> don't chicken out when you come to the edge', 

Well, once again, just "push the edge" by changing the plot range...

> but at the same time 
> "don't ask me to derive some function to fit my data, just use the
> points I gave you".

Ah OK. I'm afraid you gonna have a BIG problem here. First practically, as 
there's no way a computer program can guess what curve to draw through some 
points (you have to tell it first), second theoretically, as you can force 
whatver polynomial function of high enough order to go thru your points : and 
then what ? Would it make any sense ? In order to extrapolate results, you 
first have to understand how your dataset work.

> And "you were plotting nicely with that data
> file I gave you, don't ask me to wrack my brains to write a function,
> I won't blame you if it's just a guess where to extend those lines,
> just keep on...(until the new edge I specify beyond the data points.)"

Well, from me to you, that'd be pretty cool if it could be done in a 
meaningful way. But well, I'm afraid we'll have to wait till computers can 
read our mind (and I just can't wait for that day)

> I mean can't gnuplot make some best fit parabola or something for the
> given points? Well, "tell it not to chicken out but just keep going to
> infinity".

Frankly, the easiest way is to fit whatever simple function you feel would go 
through your data, and change the plot range. But once again, you need to 
have sort of an idea of how your data should behave. 

If you really wanna have a 'curve that goes thru the data till whatver range 
no matter any lack of sense it could be': export your plot to a bitmap, and 
use gimp or photoshop to draw the curve you'de like to see. I'm barely 
joking, it can help you figure what kind of function you could fit

Good luck anyway

-- 
Soil & Water Laboratory
Dept. of Biological & Environmental Engineering
Cornell University
Riley-Robb Hall
ITHACA, NY 14853