[GiNaC-devel] Bug(?) in reposition_dummy_indices: test case and patch

[Sheplyakov Alexei]

On Wed, Aug 30, 2006 at 12:08:26PM +0200, Chris Dams wrote:
> > This simple program
> >
> > [...]
> > 
> > fails (both with GiNaC 1.4 CVS and 1.3.x). I believe that the reason 
> > is bug in indexed.cpp:reposition_dummy_indices() and propose attached
> > patch to fix it. Note that patch *seems* to be correct, but IMHO it
> > is somewhat ugly and probably inefficient. Could anyone suggest a better
> > solution?
> 
> What if we simply don't do this kind of toggling of the variance in the
> case that both indices of the dummy pair belong to the same indexed object
> and the indexed object has a symmetry in which the dummy pair is involved?
Then

T.mu.nu~mu~nu - T~nu~mu.nu.mu

where T has cyclic symmetry, would not evaluate to zero. Which is (IMHO)
very bad thing...

> Seems simpler to me.

There exist a lot of simple *incorrect* solutions :)

Best regards,
 Alexei

-- 
All science is either physics or stamp collecting.

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