Maxima is really much simpler to use than you image, partly because your
preconceived notions are colored by previous experience with languages that
are much more restricted.
Try this:
foo():=block([],local(b),b[[1,2,3]]:x1, b[[6]]:x2, b[foobar/7]:x3, print
(arrayinfo(b)), listarray(b));
You can get the indices in use, and the values in use, in an indexed data
structure that you could use as an array, or you could use as something
else.
> -----Original Message-----
> From: maxima-bounces at math.utexas.edu
> [mailto:maxima-bounces at math.utexas.edu] On Behalf Of Fabrizio Caruso
> Sent: Tuesday, June 19, 2007 2:05 AM
> To: Robert Dodier
> Cc: maxima at math.utexas.edu
> Subject: Re: [Maxima] arrays/lists with multi-idices
>
> Hi again,
>
> Sorry, but I haven't still understood how to use
> arrays with list indeces.
>
> What I need to do is simply a procedure deCasteljau(...,n,deg)
> that works with b[a_1,a_2,...,a_n]
> or b[[a_1,a_2,...,a_n]], 0<=a_i<=deg,
> where n is passed as a parameter, i.e.
> multi-indeces whose arity is given by a parameter.
>
> The algorithm we are trying to implement
> is the multivariate "de Casteljau algorithm"
> for Bezier hypersurfaces.
>
>
> I get the following error messages:
>
> If I do:
> (%i22) foo (x) := block (local (b), array (b, 5),
> arrayapply(b,[1,2,3]) :
> x, listarray (b));
> (%i23) foo(10);
> "
>
> I then get:
> "
> Improper value assignment:
> arrayapply(b, [1, 2, 3])
> #0: foo(x=10)
> -- an error. To debug this try debugmode(true);
> "
>
> If I do
> "
> (%i26) foo (x) := block (local (b), array (b, 5), b[[1,3,4]] : x,
> listarray (b));
> (%o26) foo(x) := block(local(b), array(b, 5), b : x,
> listarray(b))
> [1, 3, 4]
> (%i27) foo(10);
> "
> I get:
> Array b has dimensions [5], but was called with [[1,3,4]]
> #0: foo(x=10)
> -- an error. To debug this try debugmode(true);
> "
>
> Fabrizio
>
>
>
>
> On Mon, 18 Jun 2007, Robert Dodier wrote:
>
> > On 6/18/07, Fabrizio Caruso <caruso at dm.unipi.it> wrote:
> >
> > > Sorry but I don't know hot to force arrays to be local.
> > > There must be something I am missing.
> > >
> > > For instance:
> > > foo(x):= block([b],b:make_array('hashed,3),b[1]:x);
> > >
> > > will change b[1] after its execution.
> > >
> > > Moreover I would like to use things like
> > > b[5,2,3,4] where the number of arguments is a parameter.
> >
> > Fabrizio, (1) local(a) within a block saves and restores the
> > properties (including some varieties of arrays) of a when the
> > block is entered and exited. (2) For Maxima arrays
> > implemented as Lisp hashtables, the number of indices is
> > immaterial; a hash key can be a list of indices (or anything).
> > For Maxima arrays implemented as Lisp arrays,
> > arraymake and arrayapply might be useful.
> >
> > e.g.
> >
> > foo (x) := block (local (b), array (b, 5), b[1] : x, listarray (b));
> > foo (3);
> > => [#####, 3, #####, #####, #####, #####]
> > listarray (b);
> > => (error message, b is not an array)
> >
> > bar (a, [L]) := arrayapply (a, L);
> > bar (x, i, j);
> > => x[i, j]
> > bar (x, i, j, k);
> > => x[i, j, k]
> >
> > I'm sorry that this is confusing; various ideas about arrays,
> > not entirely consistent, accumulated over the decades.
> > I think now is a good time to reconsider and maybe
> > clean up some of that stuff.
> >
> > Maybe if you say more about what you're trying to accomplish
> > we can give some advice.
> >
> > FWIW
> > Robert
> >
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