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## Re: [Axiom-math] About rewrited expressions for power, log, exp and so.

**From**: |
Martin Rubey |

**Subject**: |
Re: [Axiom-math] About rewrited expressions for power, log, exp and so. |

**Date**: |
30 Nov 2006 16:58:26 +0100 |

**User-agent**: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.4 |

Francois Maltey <address@hidden> writes:
>* Hello,*
>* *
>* I try to understand how axiom is sure in Expression domain.*
>* and what suppositions axiom does.*
>* *
>* It seems that axiom makes a lot of fuzzy simplifications.*
yes.
>* But then how can I test if standard exemples of axiom continue to be right*
>* with a new elemntry.spad ?*
Well, I'm still hoping for a unit testing package. But in fact, I wouldn't mind
if some "standard example" stops working, but in exchange a dozen others start
working.
The "simplifier" in EXPR is nearly non-existent, and those bits that do exist
are quite broken.
>* sqrt (u^2) ---> sqrt (u^2) I agree sqrt ((-1)^2) = 1*
>* but (u^a)^(1/a) ---> u not coherent with a=2*
quite right. In fact, I believe I corrected this behaviour in "hackroot"
once. I didn't realize that there were other places with that nonsense, too.
>* What rules might apply axiom for expressions ? Is there a reason that theses*
>* rules aren't usual mathematic rules ? What is the axiom policy ? What is*
>* your advice ?*
My advice is: look at MuPaD and see how things are done there. I think they got
it right.
Apart from that, implement many good computable domains.
Great that you are working on this stuff.
Martin