[Maxima] display all results of sqrt()

[Stavros Macrakis]

Oops, actually, the naive result of expand(expr^2) if each oneof is
independent is 4,6,7,9.

On Wed, Aug 19, 2009 at 2:56 PM, Stavros Macrakis<macrakis at alum.mit.edu> wrote:
> The problem here is with correlated expressions. Consider
>
>     expr: oneof(1,2)+1
>
> Presumably expr^2 can take on the values 4 and 9.  But what about
> expand(expr^2)?  Surely that should also take on the values 4 and 9,
> and not 4, 6, and 9...
>
>            -s
>
> On Wed, Aug 19, 2009 at 2:43 PM, Barton Willis<willisb at unk.edu> wrote:
>> Some time ago, I had the idea of a "one_of" object. Such an object
>> might be useful when an expression has multiple representations (say
>> the Gauss hypergeometric functions with all six linear
>> transformations). In the end, the user could choose the "best" of the
>> alternatives. I didn't pursue the idea, but to start it was something
>> like:
>>
>>  (%i46) one_of_p(e) := not mapatom(e) and op(e) = 'one_of$
>>
>>  (%i47) load("simplifying")$
>>
>>  (%i48) simp_one_of([e]) :=  block([p : [], q : []],
>>  e : listify(setify(e)),
>>  if e # [] and rest(e) = [] then first(e)
>>  else (
>>  for ek in e do (
>>     if one_of_p(ek) then p : append(p, args(ek)) else q : cons(ek,q)),
>>  simpfunmake('one_of, listify(setify(append(p,q))))))$
>>
>>  (%i49) simplifying('one_of,'simp_one_of)$
>>
>>  (%i50) one_of(a,one_of(a,b,c));
>>  (%o50) one_of(a,b,c)
>>
>> Doing arithmetic on one_of objects isn't particularly difficult, but
>> doing it automatically via tellsimpafter is out of my league. For such
>> tasks, I think it would be easier to have a automatically applied
>> optional post simplification function. Such a function could look for
>> and crunch sums / products / ...  of 'one_of' expressions.
>>
>>
>> Barton
>>
>> -----maxima-bounces at math.utexas.edu wrote: -----
>>
>>>To: Leo Butler <l.butler at ed.ac.uk>
>>>From: Robert Dodier <robert.dodier at gmail.com>
>>>Sent by: maxima-bounces at math.utexas.edu
>>>Date: 08/19/2009 01:21PM
>>>cc: maxima at math.utexas.edu, "Grasemann,  Karsten"
>>><karsten.grasemann at geagroup.com>
>>>Subject: Re: [Maxima] display all results of sqrt()
>>>
>>>On Wed, Aug 19, 2009 at 7:50 AM, Leo Butler<l.butler at ed.ac.uk> wrote:
>>>
>>>> (%i2) sqt(x) := block([], if listp(x) then map(sqt,x) else
>>>> [-sqrt(x),sqrt(x)]);
>>>
>>>I can't really do justice to this topic, so I'll settle for quibbling
>>>today ...
>>>
>>>I want to discourage cruft. The "block" construct isn't needed, and
>>>even if there were multiple expressions, in the absence of local variables
>>>you can write just (e1, e2, e3) . It's hard enough to understand
>>>what's going on without extra clutter.
>>>
>>>Aside from that, this question of representing multiple values is
>>>very interesting and I'm pretty sure we could figure out a way to
>>>handle it in a way that is both useful and well-founded. It seems likely
>>>that multiple values could be represented as sets. We probably
>>>have to strengthen Maxima's ability to handle sets to make it work.
>>>
>>>FWIW
>>>
>>>Robert Dodier
>>>_______________________________________________
>>>Maxima mailing list
>>>Maxima at math.utexas.edu
>>>http://www.math.utexas.edu/mailman/listinfo/maxima
>>
>>
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>