On Fri, Mar 18, 2011 at 2:44 PM, Sherjil Ozair <sherjiloz...@gmail.com>wrote:
> Hello Hector, > > limit(sin(x),x,oo) means sin(x) evaluated, as x approaches to infinity from > default positive side. > My apologies. I read it as sin(x)/x . > It is an oscillatory limit, equal to k and not k/oo, where k can be > anything in [-1,1]. > The answer should be Nan, and not an error, as then, sympy would be more > robust, and users will be able to use the math.isnan() function to check if > a limit is defined or undefined. > But why should it be NaN? As far as my little knowledge goes, NaN should be of the form 0/0 or oo/oo or 0*oo or 0**0 or 1**oo or oo**0. http://en.wikipedia.org/wiki/NaN ( Creation ) lim(sin(x),x,oo) is definitely not any of these types. > > Regards, > Sherjil > > While checking for this things, I find something really wearied. In [33]: import sympy as syp In [34]: syp.limit(syp.abs(x)/x,x,0,dir='+') Out[34]: 1 In [35]: syp.limit(syp.abs(x)/x,x,0,dir='-') Out[35]: -1 In [36]: syp.limit? Type: function Base Class: <type 'function'> String Form: <function limit at 0x8f7b64c> Namespace: Interactive File: /usr/lib/pymodules/python2.6/sympy/series/limits.py Definition: syp.limit(e, z, z0, dir='+') Docstring: Compute the limit of e(z) at the point z0. z0 can be any expression, including oo and -oo. For dir="+" (default) it calculates the limit from the right (z->z0+) and for dir="-" the limit from the left (z->z0-). For infinite z0 (oo or -oo), the dir argument doesn't matter. Now mathematically, limit x tending to 0, abs(x)/x should not exist. But SymPy doesn't warn about this during its execution nor in the documentation. This might be confusing for complete beginner or in other cases. > > On Fri, Mar 18, 2011 at 2:34 PM, Hector <hector1...@gmail.com> wrote: > >> >> >> On Fri, Mar 18, 2011 at 4:57 AM, Aaron S. Meurer <asmeu...@gmail.com>wrote: >> >>> For issue 2200, we didn't decide if limit(sin(x), x, oo) should raise an >>> error or should return nan (or something else). >>> >> >> Hello everyone, >> >> Hi Aaron, I was wondering why limit(sin(x),x,oo) should have any other >> value than 0 ? >> Is it not equal to k/oo where k is some finite number in [-1,1], which >> clearly tends to zero ? >> Please tell me is there any flow in my thinking or if I am missing >> something or is it because something related to SymPy. >> >> >> >>> Aaron Meurer >>> >>> On Mar 17, 2011, at 1:25 PM, Chris Smith wrote: >>> >>> > SherjilOzair wrote: >>> >> Mr. Ronan, >>> >> You've been a great help. Please help me start up my suggesting me a >>> >> small project or patch. >>> >> I would be very grateful. >>> >> >>> > Issue 2180, 2198 or 2200. >>> > >>> > -- >>> > 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. >>> > >>> >>> -- >>> 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. >> > > -- > 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.
