On Sat, Jul 23, 2011 at 5:28 PM, Matthew Brett <matthew.br...@gmail.com> wrote: > Hi, > > On Sun, Jul 24, 2011 at 12:23 AM, Aaron Meurer <asmeu...@gmail.com> wrote: >> Note that Float(1) is not the same as Float(1.0). Fredrik or someone >> else would have to explain the details, but I think the reasoning >> behind Float(int) => Integer is something related to precision. > > Right, sorry, I should have added that: > > sympy.Float(1.0) == sympy.numbers.One()
==, yes, but is, no. In [2]: Float(1.0) is S.One Out[2]: False In [3]: Float(1.0) == S.One Out[3]: True == works because of some type casting. You also get, for example: In [4]: 0.5 == Rational(1, 2) Out[4]: True > >> Also, as the commit message notes, there is the following >> inconsistency in 0.6.7: >> >> In [1]: -1.0*x >> Out[1]: -1.0⋅x >> >> In [2]: 1.0*x >> Out[2]: x > > To me, that inconsistency is a benefit. Is there some disbenefit? > I'm asking honestly. For me it is just a question of reduced > readability in doctests and examples. > > Cheers, > > Matthew > Yes, I think there is a disbenefit, because you loose the precision information in 1.0 when you convert it to S.One. This will happen when you use Floats. They are assumed to be close to (up to their precision), but not necessarily equal to the numbers the represent. So with the default precision of 15 or something like that, 1.0 is really 1 +- 1e-15. If you really want exact numbers (i.e., rationals), you should use them. Otherwise, SymPy assumes that Floats are not exact, and treats them as such. Others, if any of this is not true, please correct me. By the way, if you want to convert from floats to rationals, you can use nsimplify: In [14]: nsimplify(1.0*x, rational=True) Out[14]: x Aaron Meurer -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to sympy@googlegroups.com. To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
