On Wed, Apr 13, 2011 at 11:37 PM, Tom Bachmann <ness...@googlemail.com>wrote:
> How do you plan on implementing limits of bivariate functions? > Computing them is a *very* nontrivial extension over univariate limits > (as far as I can tell) ... > > To find limit at (x,y) = (0,0) replace "y" by "mx" and check whether the given limit is independent of "m" or not. If it is independent, than limit exists and otherwise not. *function.subs* will be handy for this. This idea can be extended for any general point (a,b) in plane with first I need to shift the origin to that point and than applying the same logic. I might come up with better method and handling extreme cases ( like x/y -> oo) during coding but this is my initial approach. But before that, I should make sure that this developers are happy with this change. > On 13 Apr., 16:45, Hector <hector1...@gmail.com> wrote: > > Hello groups, > > > > This is about the way limit has been defined in sympy. Currently, Sympy > > gives following result. > > > > In [1]: limit(abs(x)/x,x,0) > > Out[1]: 1 > > > > But as we know, the right-hand and left-hand of limit at given function > is > > different. > > > > In [2]: limit(abs(x)/x, x, 0, dir = "+") > > Out[2]: 1 > > > > In [3]: limit(abs(x)/x, x, 0, dir = "-") > > Out[3]: -1 > > > > And hence mathematically speaking, limit doesn't exist at given point. > Sympy > > assumes dir = "+" by default and hence giving the wrong answer. The > similar > > type of discussions has been made some times ago in Issue1000[1]. As > > suggested in discussions, the default dir should be " r " for real line > > where it checks both right hand side and left hand side limit and returns > > the answer iff both are equal. For this to happen, I am proposing that we > > should rename current "limit" function by "limit_eval" and define new > limit > > function which checks both right hand limit and left hand limit. > > > > I made the necessary changes, and the corresponding pull request is > #219[2]. > > If this changing definition things is fine with core developers, I would > > like to proceed further for limts of bi-variant functions. > > > > -- > > -Regards > > Hector > > > > Whenever you think you can or you can't, in either way you are right. > > > > [1] > http://code.google.com/p/sympy/issues/detail?can=2&q=1000&colspec=ID%... > > [2]https://github.com/sympy/sympy/pull/219 > > -- > 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. > > -- -Regards Hector Whenever you think you can or you can't, in either way you are right. -- 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.
