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 <distantjob...@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+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/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+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/CAKgW%3D6LynWr9OeFAP6CpTqN3tKSw3bWdOO5hTMtH6z2d7bnM7w%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
