Re: Re: Re: Re: Mathematica language issues

*To*: mathgroup at smc.vnet.net*Subject*: [mg53165] Re: [mg53142] Re: [mg53112] Re: [mg53050] Re: Mathematica language issues*From*: DrBob <drbob at bigfoot.com>*Date*: Mon, 27 Dec 2004 06:41:36 -0500 (EST)*References*: <200412241058.FAA05777@smc.vnet.net> <200412250900.EAA18524@smc.vnet.net> <97F219DA-567C-11D9-8E89-000A95B4967A@mimuw.edu.pl> <opsjknlip6iz9bcq@monster.ma.dl.cox.net> <DCEFA273-56E9-11D9-9B3E-000A95B4967A@mimuw.edu.pl>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

>> Occasionally WRI admits that this behaviour is not what they intended and >> it then is officially classified as a bug. I don't think I've ever heard of a case like that. At most, some employee says, "That may be a bug," or "That looks like a bug." There's never anything official about it, AFAIK. Is there an official bug list that mortals can reach? I never heard of any. > I can't prove it but it would make an interesting > theorem which, in the spirit of Chaitin's algorithmic information > theory, we could state by saying that Mathematica is > information-theoretically incompressible ;-) Granted, Godel's Incompleteness theorem rules us all. No getting around that! Still, I recommend someone add the Villegas paper to Help. Bobby On Sun, 26 Dec 2004 11:57:21 +0900, Andrzej Kozlowski <akoz at mimuw.edu.pl> wrote: > > > Correctness in the strict sense does not seem to be an issue here. > Because it does not give you access to the source code Mathematica > documentation consists either of "models" , rather like Fred's, or > examples of usage from which the user is supposed to work by analogy to > deduce what will happen in other cases. Neither of these approaches > gives you full knowledge and always there is some remaining "mystery". > Sometimes when working by analogy and attempting inputs that were not > actually explicitly mentioned in the documentation you will soemtimes > discover that they do not work as you had expected. Occasionally WRI > admits that this behaviour is not what they intended and it then is > officially classified as a bug. Sometimes, however, it turns out to be > an exception that was merely "undocumented". But what does that really > mean? Obviously documentation does not mean listing all possible inputs > and all possible outputs; even if such a thing were possible it would > not be very useful. How can this be corrected? Well, either by creating > a more complicated model (like the one Fred has now proposed for the > operation of Times and Plus) or by giving some extra examples or > counter-examples, e.g saying explicitly: a+b+c/.s:a+b->0 will not > work. But the situation seems to be rather like with Goedel's > Incompletness; adding such things to the documentation will almost > certainly lead to new exceptions. In the end it may be that the only > complete and correct documentation of Matheamtica would have to consist > of its source code. I can't prove it but it would make an interesting > theorem which, in the spirit of Chaitin's algorithmic information > theory, we could state by saying that Mathematica is > information-theoretically incompressible ;-) > > > Andrzej > > On 26 Dec 2004, at 01:18, DrBob wrote: > >>>> If Fred's "speculations" came form an employee of WRI they could >>>> have the status of "documentation" without changing a word. The >>>> mystery here is simply a question of authoritativeness. >> >> If he's correct, you mean. >> >> Bobby >> >> On Sat, 25 Dec 2004 22:55:10 +0900, Andrzej Kozlowski >> <akoz at mimuw.edu.pl> wrote: >> >>> *This message was transferred with a trial version of CommuniGate(tm) >>> Pro* >>> I am sure Fred will provide his own answers, but on the principle "the >>> more the merrier" (especially at Christmas) , I thought I would >>> contribute my own comments: >>> >>> On 25 Dec 2004, at 18:00, DrBob wrote: >>> >>>> Fred, >>>> >>>> At several points you made statements I simply don't understand. The >>>> examples clarify what you meant for the most part, but I'm still >>>> wondering, so here goes: >>>> >>>>>> Unevaluated is meant to pass unevaluated arguments to a function >>>>>> body and as such it works perfectly. No one in practice is >>>>>> interested >>>>>> in (1+1)*Unevaluated[2+2]. >>>> >>>> Do you mean a Function body? If not, Times in that example qualifies >>>> as a function body. (I think.) >>> >>> One uses Unevaluated to prevent a rule from being applied. This means >>> that a rational person will only do it when he knows there is a rule >>> that he does not want to be used. There is no normal situation where >>> one would use Unevaluated and there was no specific evaluation one >>> wanted to prevent. >>> >>>> >>>>>> If now no rules for f can be applied, Mathematica returns the >>>>>> result >>>>>> so far, with Unevaluated wrapped again around the labeled >>>>>> arguments. >>>> >>>> So it's only rules FOR F that matter? Does the distributive property >>>> count as a rule for Times? >>> >>> You do not need Unevaluated to prevent the distributive rule being >>> used >>> because it is never used automatically. You need to apply something >>> like Distribute etc. >>> >>>> >>>>>> If a rule for f can be applied, the administration of arguments >>>>>> that come from Unevaluated is completely skipped. >>>> >>>> I don't get any meaning from the phrase "administration of >>>> arguments". >>> >>> I think Fred meant that the rule is applied to the arguments "as >>> given", without changing them or rearranging in any way. >>> >>>> >>>>>> I first formulate my assumption (only WRI and maybe a few others >>>>>> know if I am right!) >>>> >>>> Even if your assumption is correct (as I suspect it is), this >>>> statement doesn't really square with a later claim that there's no >>>> mystery. >>> >>> A certian mystery exists even when we have full documentation, because >>> even that is only a description of expected behaviour of Mathematica >>> and does not include the actual mechanism behind the behaviour (of >>> which at most a vague idea is provided). Everything else requires the >>> source code. If Fred's "speculations" came form an employee of WRI >>> they >>> could have the status of "documentation" without changing a word. The >>> mystery here is simply a question of authoritativeness. >>> >>> >>> Andrzej Kozlowski >>> Chiba, Japan >>> http://www.akikoz.net/~andrzej/ >>> http://www.mimuw.edu.pl/~akoz/ >>> >>> >>> >>> >> >> >> >> -- >> DrBob at bigfoot.com >> www.eclecticdreams.net >> >> > > > > -- DrBob at bigfoot.com www.eclecticdreams.net

**References**:**Re: Re: Re: Mathematica language issues***From:*"Fred Simons" <f.h.simons@tue.nl>

**Re: Re: Re: Mathematica language issues***From:*DrBob <drbob@bigfoot.com>

**Re: Re: Re: Re: Mathematica language issues**

**Re: Help with a summation**

**Re: Re: Re: Re: Mathematica language issues**

**Unevaluated, Plus and Times (was Re: Re: Re: Re: Mathematica language issues)**