02.05.2011 20:25, Ronan Lamy пишет:
Le dimanche 01 mai 2011 à 23:37 -0700, Ondrej Certik a écrit :
You should assume it. Non commutative symbols are just making things
very complicated, and it was a mistake to add them into the core of
sympy. They should start in sympy.quantum, and only after they are
being used a lot, we should start thinking how to handle them
properly.
I agree on this. Non-commutative Symbols don't make a lot of sense. If
we didn't have them (and severed the inheritance from Boolean), we could
say that Symbols are complex variables. Instead, we have a murky
definition.
Anyway, is_commutative is just an extreme example. Most .__new__()
and .eval() methods check one assumption or other. We'd have to throw
all that code away and rewrite it from scratch.
Non-commutative Symbols are generalization, commutative Symbols are
specialization. (Remarking that it is a pure mathematica, not a quantum
- because there are no physical lows used when we consider
Non-commutative Symbols),
but I agree that temporary it can be placed in sympy.quantum for tactic
aims.
In any case it would be convinient (and for effective core - to avoid
unnesesary checking) to isolate in the core the possibility to work with
commutative Symbols and possibility to work with non-commutative Symbols
(or even with non-associative symbols). Now, as I understand, in the
SymPy core the non-commutative core is not isolated, and at the same
time by defult the is_commutative is switch off (False) - but many
unnecessary checking are used further and we continue to deal with
commutative.
So the isolation is needed in any case (effective core) - even after "we
should start thinking how to handle them properly".
May be the interface of objects can be used for this.
This type of assumption is classified as related with algebraic
fields/rings. (For this type of assumptions may be meaningless to attach
assumption to symbols at whole )
--
Alexey U.
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