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] <javascript:>> > 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] <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/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]. 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/2d41dd13-587e-4fca-996f-e3892b9fe792%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
