On Wed, Jan 14, 2015 at 12:02 AM, Chris Smith <[email protected]> wrote:
> By allowing the (-1)**(1/3) to remain we leave open (as with Rational > bases) the option of getting to the real root with real_root. I wish we had > a good mechanism to check if something like root(x, 3) + 2 == 0 when > substituting in -8 for x. It is for this reason that the following returns > no solution: > > >>> solve(root(x,3)+2) > [] > I suppose this is right. There is no x that when plugged in to that equation, gives 0. Maybe 8*exp_polar(3*pi*I) could be considered a solution. Aaron Meurer > > On Tuesday, January 13, 2015 at 3:20:46 PM UTC-6, Aaron Meurer wrote: >> >> Without commenting on your proposal, I'd like to point out that point of >> the principal nths root is that all other nth roots are the powers of that >> root. >> >> Aaron Meurer >> >> On Tue, Jan 13, 2015 at 3:14 PM, Chris Smith <[email protected]> wrote: >> >>> In PR 8814 <https://github.com/sympy/sympy/pull/8814> I write, >>> >>> >>> Something has to be done to allow one to compute real_root(float, odd) >>> as real. At first I thought to handle this in real_root, but then I thought >>> it might be better to catch it in _eval_power itself. Which do you think is >>> better: >>> >>> # This is how a negative rational base behaves: >>> >>> root(S('-1/10'),3) >>> (-1)**(1/3)*10**(2/3)/10 >>> # Now, for a negative float... >>> >>> root(S('-.1'),3)0.464158883361278*(-1)**(1/3) # <-- should a negative >>> >>> float give this (a)>>> _.n()0.232079441680639 + 0.401973384383085*I # >>> >>> <-- or this (b)? >>> >>> The SymPy trend is to fully evaluate an expression if args are numbers, >>> but by selecting the principle root in the case of Pow, the user looses the >>> option to select the real branch post-calc. (Hence, I favor not fully >>> evaluating in this case, selecting behavior (a).) If the power is not an >>> odd rational, the usual, fully evaluated result is obtained. >>> >>> >>> /c >>> >>> -- >>> 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/da5b3c19-ef67-4bcd-b5c3-b6c167bd378d%40googlegroups.com >>> <https://groups.google.com/d/msgid/sympy/da5b3c19-ef67-4bcd-b5c3-b6c167bd378d%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> 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/5dd074d2-2156-41e0-a6e0-ed6e0d3e8771%40googlegroups.com > <https://groups.google.com/d/msgid/sympy/5dd074d2-2156-41e0-a6e0-ed6e0d3e8771%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > 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/CAKgW%3D6%2BCV6GyXYmiCTSTiSNiy0GEXvoYbVEuQuD%3D8boA6DGEHA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
