On Sep 13, 5:53 pm, Mitesh Patel <qed...@gmail.com> wrote: > On 09/12/2010 10:19 PM, mda_ wrote: > > > On Sep 12, 5:44 pm, Mitesh Patel <qed...@gmail.com> wrote: > >> [...] > >> This appears to work: > > >> sage: bool(e^(-pi/2) == i^i) > >> True > > > Thanks Mitesh. What is the sage convention for returning the object > > as a result of "==" instead of bool when the result is not False? Is > > it ad hoc? > > I can't give an authoritative answer. As far as I can tell, just > symbolic relations are not immediately checked for truth. For example, > > sage: 3 <= 3 > True > sage: 3 <= SR(3) > 3 <= 3 > sage: bool(3 <= SR(3)) > True > sage: e == 3 > e == 3 > sage: bool(e == 3) > False > > The bool calls here call Expression.__nonzero__, which is documented in > > SAGE_ROOT/devel/sage/sage/symbolic/expression.pyx > > In particular, > > Return True unless this symbolic expression can be shown by Sage > to be zero. Note that deciding if an expression is zero is > undecidable in general. > > > Would you consider float(i^i) raising TypeError a bug? > > I believe this happens because Expresssion.__float__ uses just Pynac to > simplify i^i. However, if it's necessary, we fall back to Maxima to > check whether i^i equals e^(-pi/2).
Does sage publish its formal grammar (BNF)? Perhaps doing so would be useful. There are several free tools available: ANTLRWorks, Bison, Lisp _. Regards, Don -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
