Dear Josie,
I fear that what you're asking for would be very difficult to implement (to
say the least); for canform, the renaming of indices is an essential part of
the simplification process, as this is how canform creates a "normalized"
version of tensor (sub)expressions before elimination. Without renaming,
canform would become essentially worthless.
By way of one particular example, suppose we have a sum of two
subexpressions, one using i the other using j as dummy indices, for which we
set properties. Suppose that canform recognizes that after
renaming/rearranging, the two subexpressions are really the same, and can be
combined into one. Which name should it then use for the dummy index, i or
j? If it preserves both, it cannot do the simplification, since the two
subexpressions remain different, defeating the basic idea behind bringing
tensors to CANonical FORM for simplification.
Viktor
-----Original Message-----
From: maxima-bounces at math.utexas.edu [mailto:maxima-bounces at math.utexas.edu]
On Behalf Of josie.huddleston at durham.ac.uk
Sent: Monday, January 21, 2008 11:20 AM
To: maxima at math.utexas.edu
Subject: Request for itensor's symtry.lisp
Hiya - I've been working on a program with itensor using my own indices that
are
specified to have certain properties outside the scope of itensor. My
problem
is that when using canform to simplify using tensor symmetries, any internal
indices are automatically turned into normal itensor dummies, thus
losing all the properties I've set for them.
So I was wondering if the symmetry workings of canform (and particularly
internal function canprod, which I think is where the trouble lies) could be
separated from the renaming features somehow, so that one could be called
without the other? Or if they can't, perhaps a new optional argument to
canform
that would suppress renaming tendencies...? If this modification isn't
wanted
for the released version, could I at least have a hint of what'll need
changing to
create my own version of canform for my program?
Thanks,
Josie
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