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 <[email protected] > <javascript:>> 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 <[email protected]> > 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 <[email protected]> > 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 [email protected]. > >> >> > To post to this group, send email to [email protected]. > >> >> > 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 [email protected]. > >> > To post to this group, send email to [email protected]. > >> > 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 [email protected] <javascript:>. > > To post to this group, send email to [email protected] > <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/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 [email protected]. To post to this group, send email to [email protected]. 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.
