# [Maxima] limit of erfc

Richard Fateman fateman at eecs.berkeley.edu
Thu May 17 16:20:47 CDT 2012

```On 5/17/2012 1:37 PM, Raymond Toy wrote:
>
>
> On Thu, May 17, 2012 at 1:02 PM, Stavros Macrakis
> <macrakis at alum.mit.edu <mailto:macrakis at alum.mit.edu>> wrote:
>
>     On Thu, May 17, 2012 at 3:50 PM, Raymond Toy
>     <toy.raymond at gmail.com <mailto:toy.raymond at gmail.com>> wrote:
>
>
>         I take this to mean we shouldn't have atan(inf) -> %pi/2.
>         Which means erf(inf) and friends should just return a noun.
>         But 0*inf always returns 0. Shouldn't we return und for that?
>
>
>     We should either return und or leave it unsimplified.  Similarly
>     for inf-inf, inf^0, is(equal(inf,inf)), etc. which currently
>     return nonsense results.
>
This topic has been addressed a few times.  One (probably incomplete)
solution is to
represent inf  as  a rational number type,   (1/0),  und as (0/0)  minf
as (-1 / 0)  and combine them
as appropriate.

((rat) 0 0)  multiplied by <anything>   is then   0*anything / 0   or
und.   (that is,  ((rat) 0 0). )

oddly enough, a lot of the work is done by REMOVING code, namely no
longer checking
for division by zero.

some additional code to display 0/0 as und etc.

I wrote a paper on this...

RJF

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