Re: Difference table via DifferenceDelta[ ]. Why do I need two Table[ ] calls?

*To*: mathgroup at smc.vnet.net*Subject*: [mg121172] Re: Difference table via DifferenceDelta[ ]. Why do I need two Table[ ] calls?*From*: "Alexey Popkov" <lehin.p at gmail.com>*Date*: Fri, 2 Sep 2011 03:29:15 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <j3l6l1$d81$1@smc.vnet.net>*Reply-to*: "Alexey Popkov" <lehin.p at gmail.com>

Christopher, DifferenceDelta is an autoloaded function: In[1]:= ClearAttributes[DifferenceDelta, {Protected, ReadProtected}] Definition[DifferenceDelta] Out[2]= DifferenceDelta := System`Dump`AutoLoad[Hold[DifferenceDelta], Hold[DifferenceDelta], Discrete`DifferenceDelta`] /; System`Dump`TestLoad The need for Evaluate in your code is an inconsistency: such code should work well without beating the HoldAll attributes of Table. And error messages when your code is evaluated without Evaluate clearly show very bad design of this function. I recommend do not rely on such functions. As for why you have to evaluate your code twice, you may be interested in this thread: http://stackoverflow.com/questions/5649379/why-do-i-have-to-evaluate-this-twice Alexey ----- Original Message ----- From: "Christopher O. Young" <cy56 at comcast.net> Newsgroups: comp.soft-sys.math.mathematica Sent: Wednesday, August 31, 2011 3:41 PM Subject: [mg121172] Difference table via DifferenceDelta[ ]. Why do I need two Table[ ] calls? > The following gives me a difference table for x^3, but it would be nice if > I > could do it with only 1 Table call. > > Grid[ > Table[ > Table[ > DifferenceDelta[x^3, {x, n}] // Evaluate, > {x, -6, 6 - n + 1} > ] > , {n, 1, 3} > ], > Alignment -> Right > ] > > The following hangs up, though. I have to abort it after several minutes > of > nothing happening. > > Table[ > DifferenceDelta[x^3, {x, n}] // Evaluate, > {x, -6, 6}, > {n, 1, 3} > ] > > Any help appreciated. > > Chris Young > cy56 at comcast.net > > >