[Maxima] Operations on inf

Raymond Toy raymond.toy at ericsson.com
Thu Mar 8 09:37:42 CST 2007

```>>>>> "Stavros" == Stavros Macrakis <macrakis at alum.mit.edu> writes:

Stavros> 1.  (*) text/plain          ( ) text/html
Stavros> On 3/7/07, Robert Dodier <robert.dodier at gmail.com> wrote:
>>
>> On 3/7/07, Stavros Macrakis <macrakis at alum.mit.edu> wrote:
>>
Stavros> Hmm. I think it might be unnecessarily conservative to treat actual
>> constants as potential variables. I think it would OK to treat only
>> inf and minf as potential variables (e.g. 1^inf = limit(1^x, x, inf) = 1).
>>
>> That makes 0*inf = limit(0*x, x, inf) = 0, which differs from IEEE 754
>> arithmetic rules in which 0*INF => NAN. That makes me slightly
>> uncomfortable but I could get used to it, if Maxima applies its rules
>> consistently.

Stavros> IEEE 754 makes 0*inf=nan (i.e. und) for good reason.  After all, if 1/inf =
Stavros> 0 and inf/inf = und, then it had better be true that inf/inf = inf*(1/inf) =
Stavros> und.

Stavros> Incidentally 1^inf => und differs from IEEE 754 since 1^inf => 1 there.

My knowledge of IEEE 754 is probably old, but I thought IEEE 754 only
defined the four basic arithmetic operations and sqrt.  Exponentiation
was outside the scope of IEEE 754.

Ray
```