Date: Jun 3, 2013 11:11 PM
Author: Andrzej Kozlowski
Subject: Re: Applying Mathematica to practical problems


On 3 Jun 2013, at 09:34, Richard Fateman <fateman@cs.berkeley.edu> wrote:

> On 6/1/2013 9:23 PM, Andrzej Kozlowski wrote:
>> This is one of many examples of "cross purpose" arguing. I was not
>> discussing implementing non-standard analysis at all. My point was
>> that that there is nothing logically more dubious about a finite
>> "number" x such that x+1=1 than there is about a positive "number" x
>> such that nx< 1 for every positive integer n, or, alternatively,
>> finite "number" x such that x/n >1 for every positive integer n.
>> Mathematicians often use the word "number" when referring to objects
>> belonging to some "extension" of the real line.

>
> Oh where to start. Here's one place.
>
> You say it is ok to have a number x such that x+1=1. I agree.
> I say it is NOT ok to have a number x such that x+1=x.
> You respond
> It is ok to have a number x such that x+1=1.
> Can you see the difference?


Yes, I was careless about this, but that was because it does not really
matter. It is O.K. to extend the real line to an algebraic and
topological sturcture which contains objects such x such that x+1=x.
Of course such objects do not have inverses, so you can't conclude that
0=1. Admittedly, in Mathematica the underlying logic is obscured by
the fact that it equality is not identity, so you do have

1`0 == 1

True

1`0 == 0

True

but

1`0 == 0

True

All this means that equality is a non-transitive relation on this
extended set of objects (but identity is). That is also logically
perfectly sound.

>
>
> Also is the Grobner basis program in Mathematica the fastest?
> I suspect it is not, though I have not compared it to Faugere's
> work, or other unnamed systems. Is it the only one using significance
> arithmetic? I suspect it is. What would that prove? What
> would that prove about use as a default?


This is nonsense. Faugere does not work on numerical analysis and has
not implemented a numerical Groebner basis. Other people have worked on
approximate Grobener bases using fixed precision arithmetic but (as far
as I know) there are no working implementations available.

Groebner bases with exact coefficients are an entirely different
subject, unrelated to this discussion.


>
> Finally, I would remind AK (and others)
> that proving some number of correct results
> does not prove an algorithm is correct. Proving even one incorrect
> result demonstrates a bug.
>


You have never demonstrated one incorrect result proved by Mathematica.

AK