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MathGroup Archive 2004

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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


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