[GiNaC-devel] Power laws

[Vladimir V. Kisil]

	Dear All,

	Coming back to our previous discussion (with a long history) on
  the power law (e^x)^a=e^(x*a). I am attaching a patch which does not
  break the automatic simplification exp(x)/exp(x)=1.

  I am also continuing to think on a generic tool to implement various
  transformation rules. Current "self"-isolation regime may provide a
  space for its implementation.

  Best wishes,
  Vladimir
-- 
Vladimir V. Kisil                 http://www.maths.leeds.ac.uk/~kisilv/
  Book:     Geometry of Mobius Transformations     http://goo.gl/EaG2Vu
  Software: Geometry of cycles          http://moebinv.sourceforge.net/
  Jupyter: https://github.com/vvkisil/MoebInv-notebooks
>>>>> On Tue, 15 Oct 2019 14:18:03 +0100, "Vladimir V. Kisil" <kisilv at maths.leeds.ac.uk> said:

    VVK> 	Dear Richard,
>>>>> On Tue, 15 Oct 2019 09:23:21 +0200, "Richard B. Kreckel"
    VVK> <kreckel at in.terlu.de> said:
    RK> Well, after celebrating this patch, we should discuss it
    RK> breaking check/exam_paranoia.cpp:217.

    RK> That particular check has nothing to do with the exp() function,
    RK> so we could re-write it in terms of Li2() or some other function
    RK> and be done with it.

    RK> But François Maltey objected about exp(x)/exp(x) not eval'ing to
    RK> 1 any more:
    RK> https://www.ginac.de/pipermail/ginac-devel/2009-October/001680.html

    RK> And, somehow, that should be addressed, I guess.

    VVK>     It seems that both mentioned issues are connected. I am
    VVK> attaching a revised patch which applies the law of exponents,
    VVK> but keeps exp(x)^(-1) as exp(x)^(-1). With this patch
    VVK> check/exam_paranoia.cpp (as well as all other checks) went well
    VVK> (at least on my computer.)

    RK> I propose writing generic functions outside the automatic eval
    RK> system along these lines
    RK> https://www.ginac.de/FAQ.html#treetraverse searching for common
    RK> arguments of exp() which may be combined. Would you like to
    RK> venture?

    VVK>   I will keep thinking on implementation of the rule e^t * e^s
    VVK> = e^(t+s).  At the moment, I am in a favour to make it a part
    VVK> of a more general mechanism which will allow a user to apply
    VVK> some specific transformations for particular functions on
    VVK> demand (beyond wildcard substitutions). So it will not be done
    VVK> with the automatic evaluation and will not slow down the
    VVK> traditional performance. May be it is worth to add some more
    VVK> properties like add_func(), mul_func(), ncmul_func() to
    VVK> complement the existing power_func()...

    VVK>   Best wishes, Vladimir -- Vladimir V. Kisil
    VVK> http://www.maths.leeds.ac.uk/~kisilv/ Book: Geometry of Mobius
    VVK> Transformations http://goo.gl/EaG2Vu Software: Geometry of
    VVK> cycles http://moebinv.sourceforge.net/ Jupyter (Colab):
    VVK> https://github.com/vvkisil/MoebInv-notebooks Jupyter
    VVK> (CodeOcean): https://codeocean.com/capsule/7952650/tree

    VVK> _______________________________________________ GiNaC-devel
    VVK> mailing list GiNaC-devel at ginac.de
    VVK> https://www.cebix.net/mailman/listinfo/ginac-devel

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