general inverse solver?

Yacas was completely rewritten in java (Ryacas interfaces to the
C version) since the Ryacas project started so I would not exactly
characterize yacas as dead.   The work that is going on in yacas
may not have high visibility but that does not mean there is none.

Also while Maxima is more sophisticated in terms of algorithms,
yacas is actually more sophisticated from the viewpoint of its
language  which borrows ideas from both imperative and prolog  
programming
and its interfaces are more sophisticated (it is one of the few CAS  
systems
that developed an OpenMath interface) and its socket server is
used by the Ryacas interface.  yacas can also translate math  
expressions
to TeX and do exact arithmetic.

Also to put this in the correct context, yacas does seem capable of
answering the majority of questions that are posed on r-help that need
a CAS in the answer. From a practical viewpoint it does seem to have
the facilities that are most often needed.   The Ryacas vignette has
a survey of some of its algebra capabilities.

That being said, without taking away from yacas there is work going  
on to
interface R to a second CAS.

On Tue, Feb 10, 2009 at 2:33 AM, Hans W. Borchers
<hwborchers at googlemail.com> wrote:

I know that Ryacas is promoted here whenever requests about  
symbolic algebra
or calculus appear on the R-help list. But to say the truth, Yacas  
itself is
a very very limited Computer Algebra System and looking onto its  
home page
it appears the development will stop or has stopped anyway.

It would be fair to clearly state that there is no R package to solve
somewhat more involved symbolic mathematical problems. One could  
then point
the requestor to one of the open source Computer Algebra Systems   
(CAS) such
as Maxima or Axiom.

Interestingly, the free Math Toolbox Euler by Grossmann has  
integrated
Maxima into its numerical environment in a way that is really  
useful for
numerical and symbolic computations. I could imagine that in a  
similar way
Maxima can be integrated into R bringing the full power of computer  
algebra
to the R community.

Hans W. Borchers
ABB Corporate Research

----
Postscript

"The Euler Mathematical Toolbox is a powerful, versatile, and open  
source
software for numerical and symbolic computations ... Euler supports  
symbolic
mathematics using the open algebra system Maxima."

<http://mathsrv.ku-eichstaett.de/MGF/homes/grothmann/euler/>



Gabor Grothendieck wrote:

The forms of equations are limited but its not limited to just one:

library(Ryacas)

Loading required package: XML

x <- Sym("x")
y <- Sym("y")
Solve(List(x+y == 2, x-y == 0), List(x, y))

[1] "Starting Yacas!"
expression(list(list(x == 2 - y, y == 1)))


On Mon, Feb 9, 2009 at 7:45 PM, Carl Witthoft <carl at witthoft.com>  
wrote:

Gabor G a ecrit:
Check out the Ryacas package.   There is a vignette with some
examples.

----
Which led me to the manuals for yacas itself.  I'm guessing there  
may be
a
way to use yacas'  "AND" construct to combine a few equations and  
then
hope
the Newton Solver can work with that, but it's not clear that  
will work.

TK!Solver is nice because you aren't limited to linear equations,  
nor to
equations which "fit" into a matrix structure, and because it's  
legal to
have more than one unknown to be back-solved (assuming the  
problem is not
under- or over-defined, of course).

--
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