Alasdair ,
I can't actually access that pdf, if you have it, can you email it to
me please. I am actually a Georgia Tech alumni, so if any of the
authors of that other paper are still there as faculty, I may be able
to get some help from them (I was actually an ME, so I don't know many
EE faculty).
If the approaches mentioned in these papers are only for simple
functions, it may be easier to use the built in Maxima Laplace and
then go from s to z using an approach based on evaluating residues.
This is discussed in Ogata's discrete controls and another book by
Astrom called Computer Controlled Systems. It works for proper
transfer functions with a few restrictions.
Alasdair and the rest of the list:
It seems to me like there are two approaches to symbolic z transform:
1. Find a way to get Maxima to do simplification of infinite series
like what is typically done when teaching the z transform in a digital
controls class (usually there is some explanation in an appendix like
in Ogata's book).
2. Create a fancy look up table. This is what is done with either
the z or Laplace transform after the theory is understood. I don't
know how far you could get with this approach, but it basically
involves programming some basic transforms and then some properties of
the transform to try to make an expression fit something in the table
(things like an addition property, a shifting property, ...)
Do you have any idea what the existing Laplace transform and ilt
functions do? Is it similar to either of the approaches I am
describing? Is it a look up table and rules or the actual Laplace
integral?
This may be the thing that pushes me over the edge, but I must confess
that I am not (yet) a Maxima programmer. I have done some lisp
programming to make fancy things with the Gimp, but I am far from
comfortable and haven't done it in a while. I program mainly in
Python.
Ryan
On 1/26/07, Alasdair McAndrew <amca01 at gmail.com> wrote:
> I've done some web searching, and also some database searches, and can't
> find anything about public Macsyma z-transform code. However, back in 1995,
> some code was written for REDUCE:
>
> http://www.zib.de/Symbolik/reduce/moredocs/ztrans.pdf
>
> I have no idea of the differences between Macsyma and REDUCE, and how
> non-trivial it would be to port REDUCE code to Maxima, but maybe it would be
> worth a look... the first author is now at Universit?t Kassel:
>
> http://www.mathematik.uni-kassel.de/~koepf/indexenglish.html
>
> -Alasdair
>
>
> On 1/27/07, Stavros Macrakis <macrakis at alum.mit.edu> wrote:
> > On 1/26/07, Alasdair McAndrew <amca01 at gmail.com> wrote:
> > > I think a symbolic z-transform would be a very welcome addition to
> Maxima.
> > > I don't know if commercial Macsyma ever included z-transform routines,
> but
> > > if so it should be possible to port them to Maxima (assuming that you
> can
> > > obtain the source code).
> >
> > Well, if we could (legally) obtain the source code (whether in Lisp or
> > in the Macsyma language) to commercial Macsyma, there are *many*
> > things we could improve. But as far as I know, the copyright holder
> > has no interest in releasing it under an free or open license.
> >
> > If, on the other hand, there is code developed for commercial Macsyma
> > by *outside* developers, there is a chance they can be persuaded to
> > contribute their code to the Maxima project.
> >
> > -s
> >
>
>
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