[GiNaC-devel] Matrices vs indexed

[Sheplyakov Alexei]

On Tue, Aug 01, 2006 at 04:01:09PM -0400, Alejandro Limache wrote:
> according to Ginac-mini FAQ:
> >The indexed class (and most derived classes) is intended for tensor 
> >manipulation without referring to a particular basis. Thus, the indexed 
> >class is well suited for calculations involving  (formally defined) 
> >tensor algebra of "non-integer-dimensional space".
> >....
> >In that framework, unrolling ai*ai to a1^2+a2^2+a3^2+... is not possible, 
> >since the dimension >is not integer!
 
> I am physicist (not a relativist one though).. but, is there something
> more useful than tensors representations (i.e tensor components)
> defined for integer indexes?!!!.

That depends. For calculations in perturbative quantum field theory 
withing the dimensional regularisation tensor compontents are useless
(and in fact, ill-defined).

> It is because that I always want to get the components of tensors
> (which can be arranged as multidimensional arrays/matrices)
> is that I want to be able to unroll indexed objects.
I don't think GiNaC is a proper tool for that. Something like blitz++[1],
tvmet[2], ublas[3] might be more useful for you.


[1] http://www.oonumerics.org/blitz/
[2] http://tvmet.sourceforge.net
[3] http://www.boost.org/libs/numeric/ublas/doc/index.htm

Best regards,
 Alexei.

-- 
All science is either physics or stamp collecting.

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