From: Alex Fenton <alex@...>
Date: 2007-12-17T11:40:17+09:00
Subject: Re: Curve fitting to data

Phil Rhoades wrote:

> On Sun, 2007-12-16 at 23:55 +0000, Thomas Adam wrote:
>> On 16/12/2007, Phil Rhoades <phil@pricom.com.au> wrote:
>>> People,
>>>
>>> Does anyone know of a Ruby app that will fit a curve to data eg fitting
>>> a curve to:
>>>
>>> -10 0
>>> -9  19
>> This looks like a prime candidate for GNUPlot -- which ruby has bindings for.
> 
> 
> I think GNUPlot requires the knowledge of the type of fn you are trying
> to fit - I want the software to TELL me what sort of fn it is eg for the
> data:

You can access the "R" statistical package via Ruby, which seems to have 
curve fitting capabilities. But this would involve learning R, which 
I've found to have a steeper curve than I cared to climb.

More generally, I think for most scientific purposes, it's a good idea 
to have an idea of the type of curve (power, quadratic, cubic etc) that 
might underlie the observed data. Most applications enforce this. If you 
know the general form of the equation that's being fitted ( eg ax^2 + bx 
+ c for a quadratic), it would be possible to get estimates for a, b and 
c by using eg ordinary least squares to find a solution that minimises 
the difference between observed and predicted values. How you get to 
that with acceptable time is an algorithmic question...

But nothing I know of exactly in Ruby. You might take a look at the 
source code for the website you linked to:
http://pythonequations.cvs.sourceforge.net/pythonequations/PythonEquations/DESolver/DESolver.py?revision=1.2&view=markup

Maybe a fun one for a Ruby Quiz sometime?

alex