[Axiom-developer] [#180 bug #9216 differentiating sums with respect to a bound is wrong] Old Discussion

[kratt6]

Changes 
http://page.axiom-developer.org/zope/mathaction/180Bug9216DifferentiatingSumsWithRespectToABoundIsWrong/diff
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> >  > #3148:  bug #9216 differentiating sums with respect to a 
> > bound is wrong [A]
> > 
> > in my opinion correct beyond doubt.
> 
> In the patch report you wrote:
> 
> "Mathematically axiom produces correct output now, however
> I'm not sure whether my patch is best possible.
> 
> Maybe there should be a function D in OutputForm that displays
> unevaluated differentiation. Also, I find it ugly to use the
> raw %diff operator in COMBF. Furthermore, is it necessary to
> substitute a dummy variable for the variable of differentiation?"
> 
> I am concerned that this is another case of a "quick fix" for
> which we should consider a more general solution of the kind
> that you suggest above.

In this case the situation is a tiny little bit different, since here also 
Axioms internal representation is wrong. Worse: the design of Axioms Algebra 
currently doesn't provide "unevaluated differentiation". Obviously, it was 
thought that anything can be differentiated. In fact, I'm almost sure that 
attempting to differentiate a sum by one of its bound should signal an error, 
because it is impossible to assign a mathematically correct meaning to it. In 
this sense, I'd suggest that we aim to reach consensus until end of January.


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