On Thu, Sep 26, 2013 at 6:37 PM, Aaron Meurer <asmeu...@gmail.com> wrote:
> My idea was to put assumptions on Wild expressions. I guess using the
> new assumptions system, the assumptions do not need to be, nor should
> they be, actually tied to the symbols. This will also make it easy to
> add assumptions about general expressions, not just Wilds (and make it
> easier to do the sorts of things Angus was talking about). So
> something like
>
> expr = x + 2
> a = Wild('a', exclude=[x])
> expr.match(x + a, assumptions=Q.positive(a))
>
> would work, but for
>
> expr = x - 2
>
> it would not match.
>
> One could then specify arbitrary assumptions, and match would refuse
> to return any result where the assumptions are False. Or you could add
> a flag to make it even stronger: don't return a result unless the
> assumptions are True (as opposed to None).
>
> This may be far reaching and could be a bad idea, but I think we could
> then extend the assumptions system to allow "assumptions" like
> Q.free_of(a, x) to mean that a does not depend on x, or
> Q.isinstance(a, Mul) to mean that a is a Mul.
>
> The new assumptions system is still relatively weak and needs to be
> integrated into SymPy better, so this would be a lofty goal. But
> assuming we can unify the system, and get something like
> https://code.google.com/p/sympy/issues/detail?id=3929, I think this
> would be a nice way to specify things, much better (and more powerful)
> than throwing a bunch of lambdas around.So we definitely need to implement Rubi, I created an issue for it with motivation + steps to do: https://github.com/sympy/sympy/issues/7749 a prerequisite and a separate issue is fast pattern matching, that can handle ~10,000 rules quickly, which needs to be based on a decision tree: https://github.com/sympy/sympy/issues/7748 I have explained in details how it could work there. So it will require to rewrite the pattern matching, but I think most of the things from the current one can be reused, essentially one just traverses the expression tree just like now, but for all the rules at once using a decision tree. The #7748 is independent of #7749, but I think both issues should be solved concurently, as #7749 provides an application for #7748, that needs to work well and fast. Ondrej -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sympy+unsubscr...@googlegroups.com. To post to this group, send email to sympy@googlegroups.com. Visit this group at http://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CADDwiVCFw9nFT5Tv9ooqXMUh08M7FLONP-q62DfEu%2BpO%2BGMnmg%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
