Re: libevaluator library and GSL

[James Amundson <amundson@fnal.gov>]

On Fri, 2003-09-05 at 03:14, Alberto Manuel Brandão Simões wrote:

> > I wrote a similar library about 10 years ago. Derivatives are not too 
> > difficult to implement, but the expressions become really ugly. Try to 
> > derive sin(x)^cos(x) w.r.t. x to see what I mean :-).
> 
> I have such a system in Numexp-core (http://numexp.sf.net), but as
> Kenneth said, derivatives become very ugly.
> > 
> > Simplifying expressions is a much harder job. Of course you can do 
> > simple things like (x-x) -> 0 and (1*x) -> x but (x+y)-x is not that easy.
> 
> I am doing some of these simple simplifications. Started writing a
> better simplifier by patter matching in Perl. It gives some interesting
> results, but is not a decent way.

If you are interested in symbolic algebra, there are fully functional
free software packages available. I would argue that Maxima is the most
capable of them. (I might be biased by the fact that I lead the Maxima
Project.)

If you are really interested in learning how simplifications work in
computer algebra systems, you should probably try reading at least one
book on the subject. I would recommend starting with Paradigms of
Artificial Intelligence Programming by Peter Norvig. There are many
others.

--Jim