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] > <javascript:>> 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] <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/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]. 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/503d6140-3541-42a5-95d4-9c202f7d8e4e%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
