Re: libevaluator library and GSL

[Martin Jansche <jansche at ling dot ohio-state dot edu>]

On Thu, 4 Sep 2003, Aleksandar B. Samardzic wrote:

> I've written a library
> (http://savannah.nongnu.org/projects/libevaluator/) that makes
> possible to parse strings representing mathematical functions over
> single or multiple variables and later to evaluate these functions
> for different variable values (also to create representation of
> function derivative over specified variable etc.).

I'm only speaking for myself here: I'd like to have some of this
functionality available, but in a different form.  Specifically, I'd
prefer a formula-to-code translator which, given a symbolic formula,
would generate C code with calls to GSL functions (and could possibly
have other backends in addition).  That way, I can manually change the
generated code if necessary, plus it would presumably speed things up
if one were to use optimized compiled code instead of formulas that
need to be interpreted online.

Could you tell us more about what your evaluator does?  How does it
compute derivatives?  Symbolically or numerically?  Does it simplify
formulas?  Does it look for common subexpressions?  A number of the
optimizations one might want to do could be done by a compiler
(another reason to generate C source code).

For me, what it boils down to is this: if I want to quickly optimize
or integrate a symbolic function, I use Mathematica or some other
symbolic algebra system.  I use GSL for fixed, narrow tasks that have
to be run many times; in that case I need the code to be as efficient
as possible.  Now if there were a forumla translator that could read
Mathematica formulas (it uses a nice XML encoding) or Octave formulas
etc. and spit out GSL C code, that would be very useful.

- martin