Re: Interval[{a,b}]-Interval[{a,b}] = 0?

• To: mathgroup at smc.vnet.net
• Subject: [mg66639] Re: [mg66613] Interval[{a,b}]-Interval[{a,b}] = 0?
• From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
• Date: Thu, 25 May 2006 02:58:09 -0400 (EDT)
• References: <200605240701.DAA08477@smc.vnet.net> <A22AA36D-C546-42C6-AC08-5C5D4F8C8662@mimuw.edu.pl>
• Sender: owner-wri-mathgroup at wolfram.com

```On 24 May 2006, at 19:46, Andrzej Kozlowski wrote:

>
> On 24 May 2006, at 16:01, Richard Fateman wrote:
>
>> Is this a bug or a feature?
>> Notice that Interval[{-1,1}]-Interval[{-1,1}] is Interval[{-2,2}].
>>
>> (I'm using Mathematica 5.1)
>>
>> RJF
>>
>
> I get
>
> Interval[{-1,1}]-Interval[{-1,1}]
>
>
> Interval[{-2,2}]
>
> In[6]:=
> \$Version
>
> Out[6]=
> 5.1 for Mac OS X (October 25, 2004)
>
> This is most certainly correct (as, I think, you point out in your
> post). So whatever you have found, is neither a bug or a feature of
> my copy of Mathematica 5.1. Hmm... perhaps they have some "cracked"
> copies of Mathematica at Berkley? ;-)
>
> Andrzej Kozlowski
> Tokyo, Japan

It took me more than 12 hours to understand the point of RJF's post...
I don't think putting the entire contents into the subject  and then
formulating the body so that it seems to be saying the opposite of
what one wants to say, is a good policy (if one is really hoping for
a response, of course. )

Yes, Mathematica does return

In[8]:=
Interval[{a,b}]-Interval[{a,b}]

Out[8]=
0

Obviously that is because Mathematica does implement interval
arithmetic with symbolic end points. If something is not implemented
I don't think it makes sense to call it a bug or a feature.

Andrzej Kozlowski

```

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