[GiNaC-list] Indexed vs labelled

Vladimir V Kisil kisil_v at onetel.com
Mon Jul 31 14:13:39 CEST 2006

Dear All,

Browsing email on my vacation I noticed a discussion on indexed objects. So far
my impression is that GiNaC FAQ is mainly written in do-not-do-this-and-that
style. Some active GiNaC users (e.g. me) may wish to see more positive
suggestion. For example, I would be grateful  for answering such questions:

Q4. "Indices" of various kinds proved to be useful in different areas of
mathematics, e.g. linear algebra. If present idx and varidx classes are
strictly reserved for differential geometric usage in spaces with fractional
dimensions, are there plans to add some other classes, say "labels", which may
be freely utilised for other purposes?

Q5. I need expressions of the type \sum_{j=1}^n a_j b_j for an unspecified
symbolic value n and quantities a_j and b_j *labelled* (rememberring that
_indexed_ is already copyrighted) by j in this range. Since the varidx class
for j is not encouraged and the Einstein summing convention is not "meaningful"
in GiNaC, what is the recommended way to define such a sum in my program?

Best wishes from the sunny Odessa ;-)
Vladimir V. Kisil      email: kisilv at maths.leeds.ac.uk

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