Thank you for your clarification. 在 2017年5月30日星期二 UTC-6下午2:22:04，Aaron Meurer写道： > > No, the deduction of even/odd on Add isn't implemented yet. But the > implication Implies(Q.odd(d + 1), Q.even(d)) is always true, so you > can add it to the assumed facts unconditionally. > > Aaron Meurer > > On Tue, May 30, 2017 at 3:43 PM, mike <[email protected] <javascript:>> > wrote: > > Thank you Aaron, your response is very helpful. > > > > Q.odd(d + 1) & Q.even(d) are deduced assumptions. It seems if I use the > > current method, Sympy can not get the conclusion "d is even" from "if > (d+1) > > is odd" directly. > > > > > > 在 2017年5月29日星期一 UTC-6下午9:59:11，Aaron Meurer写道： > >> > >> None in this case means that SymPy doesn't know how determine the > >> fact. It looks like the sathandlers has an even/odd fact for Mul but > >> not for Add > >> > https://github.com/sympy/sympy/blob/71eb404921a4596b9fe42a7a4a0ccfa7d63a62c0/sympy/assumptions/sathandlers.py#L339. > > > >> If I remember correctly, it's because the corresponding fact for Add > >> requires counting, and I wasn't sure how to do that efficiently > >> (without adding an exponential number of clauses for large Adds). > >> > >> You can always tell SymPy the facts that it needs to know to deduce > >> things, in this case > >> > >> >>> with assuming(Q.positive(c), Q.integer(c), Q.positive(d), > >> >>> Q.integer(d), Q.odd(c*(d + 1)), Q.odd(d + 1) >> Q.even(d)): > >> ... print(ask(Q.odd(d))) > >> False > >> > >> here >> means "implies" (you could also use Implies(Q.odd(d + 1), > >> Q.even(d))). > >> > >> Aaron Meurer > >> > >> > >> On Mon, May 29, 2017 at 9:45 PM, mike <[email protected]> wrote: > >> > Hi, > >> > > >> > I am new to learn sympy. This is a very simple question but I do not > >> > know > >> > how to deal with it. > >> > > >> > The question is: both c and d are positive integers, is c*d even if > >> > c*(d+1) > >> > is odd. > >> > > >> > my code: > >> > > >> > from sympy import Symbol > >> > from sympy.assumptions import assuming, Q, ask > >> > c = Symbol('c') > >> > d = Symbol('d') > >> > with assuming(Q.positive(c), Q.integer(c), Q.positive(d), > Q.integer(d)): > >> > with assuming(Q.odd(c*(d +1))): > >> > print(ask(Q.odd(c))) > >> > print(ask(Q.odd((d+1)))) > >> > > >> > This code works. c is odd and (d+1) is odd, but how to evaluate d is > odd > >> > or > >> > even. > >> > I run the code > >> > ask(Q.odd(d)), > >> > but the result is "NONE" > >> > > >> > Ask for help. > >> > Thanks, > >> > > >> > -- > >> > 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 [email protected]. > >> > To post to this group, send email to [email protected]. > >> > Visit this group at https://groups.google.com/group/sympy. > >> > To view this discussion on the web visit > >> > > >> > > https://groups.google.com/d/msgid/sympy/5206e651-feeb-4cd9-a4c5-ba85f17ec6f0%40googlegroups.com. > > > >> > For more options, visit https://groups.google.com/d/optout. > > > > -- > > 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 [email protected] <javascript:>. > > To post to this group, send email to [email protected] > <javascript:>. > > Visit this group at https://groups.google.com/group/sympy. > > To view this discussion on the web visit > > > https://groups.google.com/d/msgid/sympy/2d41dd13-587e-4fca-996f-e3892b9fe792%40googlegroups.com. > > > > > > For more options, visit https://groups.google.com/d/optout. >
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