On Aug 9, 2009, at 8:07 PM, Ronan Lamy wrote:
> > Le dimanche 09 août 2009 à 16:34 -0700, Luke a écrit : >>> >>> * This line suggests that it would be helpful to create an 'inverse' >>> property - less work is needed to create this inverse than for a >>> generic >>> Pow instance. >> >> Could you elaborate on what you mean here? Do you mean an inverse >> property to Pow instances which have a integer exponent? Perhaps >> 'reciprocal' instead of 'inverse'? > Yes, I guess 'reciprocal' is better. I mean a class property defined > for > all instances that would look like: > @property > def reciprocal(self): > if self.exp == -1: > return self.base > else: > return Basic.__new__(self.__class__, self.base, -self.exp) > >> >>> *I don't see the point of the third test: it's only testing that (x >>> +y)**2*(x+y)**-4 == (x+y)**-2 which isn't related to expand. >> >> Yes, you are right, it isn't testing expand but I guess it probably >> doesn't hurt to keep it in either. > No, it doesn't hurt much, but each unneeded test makes running the > full > test suite a tiny bit more painful. Maybe we should replace it with something that doesn't have automatically combining exponents, such as: (x + y)**(2 + x)*(x + y)**(-x - 4) Then it at least checks to see if multinomial is being called after power_exp. Actually this isn't guarantied, because expand hints are applied in arbitrary order. See the expand docstring. So I am not sure if this will even work, and if so if it will on every machine (with different hash values and thus different orders in the hints dict). I forget how the expand functions are structured if expand_power_exp will call expand_multinomial afterwords or not (with the deep option set to True). Otherwise I agree. It is highly unlikely that we are ever going to change the fundamental automatic simplification of (x + y)**2*(x + y)**(-4) to (x + y)**(-2), which is the same sort of thing as x*x == x**2. And if it is broken, there are plenty of other tests that will break instead (such as the specifically structured test_Mul_doesnt_expand_exp() and others in test_arit.py. Aaron Meurer > > > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sympy-patches" group. To post to this group, send email to sympy-patches@googlegroups.com To unsubscribe from this group, send email to sympy-patches+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sympy-patches?hl=en -~----------~----~----~----~------~----~------~--~---
