From: hipster <hipster@...4all.nl>
Date: 2002-01-18T23:53:19+09:00
Subject: Re: Solving equation for a variable

On Fri, 18 Jan 2002  21:23:22 +0900, Massimiliano Mirra wrote:
> In a symbolic algebra tool named Yacas, one can do the following:
> 
> In> equation := area==base*height/2
> Out> area==(base*height)/2;
> In> Solve(equation,base)
> Out> (2*area)/height;
> 
> Is there any Ruby module that allows something like that, or do you
> have any pointer to explanations of the involved algorithms?

Mupad (www.mupad.com, free for personal use) is a CAS that has many of
its algorithms (including the solver AFAICS) implemented in its own
language, so you could glark some principles from it. Look for lib.tar
in the fileset, it has all the .mu files.

The ResearchIndex (www.researchindex.com) should be able to provide
you with everything you never wanted to know about symbolic expression
manipulation, but were forced to find out ;)

I've translated a symbolic derivation algorithm from _Structure and
Interpretation of Computer Programs_ from Lisp into Ruby; this could
provide some hints for developing a symbolic solver in Ruby:

        http://www.xs4all.nl/~hipster/lib/ruby/symbolic

regards,
Michel