Thank you very much. On Monday, November 9, 2015 at 7:17:29 PM UTC+2, Aaron Meurer wrote: > > I guess you'll want to check if the base is_Number and is_negative and > do the custom logic, otherwise run the superclass eval. Something like > (untested): > > @classmethod > def eval(cls, base, exp): > if base.is_Number and base.is_negative: > # Custom logic here > else: > return super().eval(base, exp) > > Aaron Meurer > > On Fri, Nov 6, 2015 at 2:32 PM, Paul Royik <distan...@gmail.com > <javascript:>> wrote: > > Thank you. > > How to override behaviour, so that above expression, > i.e.(-1)**(2/3).is_real > > outputs True? > > > > On Friday, November 6, 2015 at 9:51:39 PM UTC+2, Aaron Meurer wrote: > >> > >> You want to override eval. Take a look at > >> http://docs.sympy.org/latest/guide.html#functions for an example. > >> > >> Aaron Meurer > >> > >> On Fri, Nov 6, 2015 at 1:42 PM, Paul Royik <distan...@gmail.com> > wrote: > >> > I decided to use "cleaner" solution: create a custom Pow subclass > that > >> > evaluates. What method should I override? > >> > > >> > On Wednesday, November 4, 2015 at 9:25:17 PM UTC+2, Aaron Meurer > wrote: > >> >> > >> >> You can generally do this sort of thing using replace(). > >> >> Unfortunately, the pattern matcher doesn't recognize rational > numbers > >> >> as a/b, so you have to do a more manual check. This should work: > >> >> > >> >> e.replace(lambda i: i.is_Pow and i.base == x and i.exp.is_Rational, > >> >> lambda i: real_root(-1, > >> >> i.exp.as_numer_denom()[1])**i.exp.as_numer_denom()[0]) > >> >> > >> >> (replace -1 with whatever value you want to replace). A "cleaner" > >> >> solution would be to create a custom Pow subclass that evaluates > like > >> >> you want, and replace instances of Pow with your class before doing > a > >> >> substitution. > >> >> > >> >> Aaron Meurer > >> >> > >> >> On Wed, Nov 4, 2015 at 1:19 PM, Paul Royik <distan...@gmail.com> > wrote: > >> >> > So, there is no way to do it using subs and/or some manipulations? > >> >> > > >> >> > real_root(-1, 3) is of no help, because I can have arbitrary > >> >> > expression. > >> >> > > >> >> > On Wednesday, November 4, 2015 at 6:29:29 PM UTC+2, Aaron Meurer > >> >> > wrote: > >> >> >> > >> >> >> You need to use real_root, like > >> >> >> > >> >> >> In [3]: real_root(-1, 3) > >> >> >> Out[3]: -1 > >> >> >> > >> >> >> In [4]: real_root(-1, 3)**2 > >> >> >> Out[4]: 1 > >> >> >> > >> >> >> SymPy, like most math libraries, uses complex roots (i.e., > principal > >> >> >> roots) because they have nicer mathematical properties. > >> >> >> > >> >> >> Aaron Meurer > >> >> >> > >> >> >> On Wed, Nov 4, 2015 at 3:30 AM, Paul Royik <distan...@gmail.com> > >> >> >> wrote: > >> >> >> > I have the following expresssion: > >> >> >> > > >> >> >> > f=x**(Rational(2,3)) > >> >> >> > > >> >> >> > How can I get 1, when substituting (-1) instead of complex > number? > >> >> >> > For now, I got complex number when run f.subs(x,-1).evalf() > >> >> >> > > >> >> >> > -- > >> >> >> > 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+un...@googlegroups.com. > >> >> >> > To post to this group, send email to sy...@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/662a2085-1030-42d5-bbde-feb524fd246c%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 sympy+un...@googlegroups.com. > >> >> > To post to this group, send email to sy...@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/c88261c0-3449-4d7a-abf8-8d28ebdca59d%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 sympy+un...@googlegroups.com. > >> > To post to this group, send email to sy...@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/503d6140-3541-42a5-95d4-9c202f7d8e4e%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 sympy+un...@googlegroups.com <javascript:>. > > To post to this group, send email to sy...@googlegroups.com > <javascript:>. > > 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/2a8b8984-c262-4b64-8c05-80deb5d74700%40googlegroups.com. > > > > > > For more options, visit https://groups.google.com/d/optout. >
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