Dear Andrew,
On Tue, Jul 05, 2016 at 11:10:46AM -0700, Andrew wrote:
> Sorry if I should post this to sage-support ...
This sounds like the right place to discuss it!
> Does CartanType currently support A_\infty? I checked the docs and it
> seems not but I wanted to check because I need this. Well, actually, I
> only need some very rudimentary combinatorial data from the Cartan
> type, that I can easily manufacture myself, but thematically I really
> should index the objects that I am playing with by the appropriate
> Cartan types as I am hoping that what I am doing will work in types
> A^{(1)}_l, A^{(2)}_{2l}, C^{(1)}_l, D^{(2)}_l and A_\infty.
Currently, there is no support for `A_\infty`. This is mostly because
most of the interesting stuff that a cartan type provides in Sage
(e.g. the Cartan matrix, ...) is returned as a non lazy object.
Could you provide a couple examples of use that you have in mind?
In the simplest form, returning a formal object with very few methods
implemented (maybe just `is_crystalographic` and friends) would be
straightforward: add a file type_A_infinity.py with a CartanType class
and whatever you want inside it, and update CartanType.__call__ to use
it as appropriate.
> Whilst looking for this I came across the following, which I guess are
> syntax errors on my part rather than bugs:
> sage: CartanType(['A',4,1]) # works
> ['A', 4, 1]
> sage: CartanType(['A',infinity])
> File "<string>", line unknown
> ^
> SyntaxError: unexpected EOF while parsing
> sage: CartanType(['A',-1])
> File "<string>", line unknown
> ^
> SyntaxError: unexpected EOF while parsing
> sage: CartanType(['A',0])
> ['A', 0]
What's happening here is that the above does not fit within the
standard input formats that Cartan type accepts; and then it gets
confused and tries to parse the string in search of one of our
shortcuts like CartanType("A3*xA2~"). Yeah, this is a bug: it should
instead return a proper not implemented error.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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