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Topic: The year of Cyber Tester
Replies: 123   Last Post: Jul 1, 2011 4:00 AM

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 Axel Vogt Posts: 1,068 Registered: 5/5/07
Re: odd simplify in Maple [was: Re: The year of Cyber Tester]
Posted: Oct 12, 2008 3:34 PM
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Robert Israel wrote:
> Axel Vogt <&noreply@axelvogt.de> writes:
>

>> Walter Roberson wrote:
>> ...

>> > The above are simple cases of obvious defects, unless you are
>> willing to
>> > define away a complete session crash as not being a "defect".
>> Vladimir's
>> > tools are more refined, finding situations where products produce
>> > dubious or decidedly incorrect answers. I don't think it would have

>> taken
>> > very long to find such a case in Matlab 2008b: all one would have to do
>> > is pull out some of the cases one had recorded against Maple, transpose
>> > them into Matlab notation, and watch as the Maple-based Matlab

>> Symbolic
>> > Toolbox
>> > reproduced the existing Maple bug. For example, Maple 12:
>> >

>> >> log(exp(RootOf(_Z*exp(_Z)))); simplify(%);
>> > Error, (in ln) numeric exception: division by zero
>> >
>> > but evalf(RootOf(_Z*exp(_Z))) is 0, and log(exp(0)) is 0 so there

>> should
>> > be no division by zero.
>> ...
>>
>> This Maple bug steps in before log, already at
>> 'simplify( exp(RootOf(exp(_Z))) )'.

>
> That is a different bug, I think. Zeros of exp(_Z) do not exist, but Maple
> does not know that, so it essentially applies the simplification rule
> f(RootOf(f(_Z))) = 0.
>
> I think what you mean is
>
> simplify(exp(RootOf(_Z*exp(_Z))));
>
> or more generally
>
> simplify(f(RootOf(f(_Z)*g(_Z))));
>
> 0
>
> If w is a zero of f(_Z)*g(_Z), we must have f(w) = 0 or g(w) = 0. I don't
> know why Maple jumps to the conclusion that f(w) = 0 here.

Thx, f(RootOf(f(_Z))) = 0 sounds like a reason to me.

I have the errors for 'exp(RootOf(exp(f(T)))); simplify(%);' as well
and dito with a factor exp(RootOf(f*exp(_Z))) or for f a function

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