Hi Anne,

It seems my example was an over simplification.

Start with the tensor power of a finite type crystal or representation.
This is a linear combination of weights with integer coefficients.
I have two methods for replacing each integer coefficient by a polynomial.
Each polynomial has positive integer coefficients and evaluated at 1 gives 
the original
integer. One method using the LiE package and plethysm in particular.
The other polynomial uses the energy function. The actual command (which I 
simplified
above) is:

 sage: sum( L.term( a.weight(), q^(a.energy_function() ) ) for a in hw ) 

where L now has coefficients polynomials in q.

One possibility would be to use classical_decomposition as you suggest and 
then
construct the crystal isomorphisms explicitly. Then using this isomorphism 
on words I can
construct the energy function on words in the ordinary crystal.

At the moment I am restricting attention to KR crystals whose classical 
decomposition
is irreducible. I have not understood if I also need to restrict to level 0.

On Saturday, November 23, 2013 10:16:39 PM UTC, Anne Schilling wrote:
>
> Hi Bruce, 
>
> If you are only interested in the classical weight, then you can do 
>
> sage: C = KirillovReshetikhinCrystal(['A',1,1],1,2) 
> sage: B = C.classical_decomposition() 
> sage: T = TensorProductOfCrystals(*[B]*3) 
> sage: L = CombinatorialFreeModule(ZZ,B.weight_lattice_realization()) 
> sage: hw = [a for a in T if a.is_highest_weight()] 
> sage: sum( L.term( a.weight(), 1 ) for a in hw ) 
> B[(3, 3)] + 3*B[(4, 2)] + 2*B[(5, 1)] + B[(6, 0)] 
>
> Best wishes, 
>
> Anne 
>
> On 11/23/13 2:13 AM, Bruce wrote: 
> > Sorry about being difficult. 
> > 
> > Here is one command: 
> > 
> > lie.p_tensor(3,[2],'A1') 
> > 
> > Here is an alternative: 
> > 
> > C = KirillovReshetikhinCrystal(['A',1,1],1,2) 
> > L = CombinatorialFreeModule(ZZ,C.weight_lattice_realization()) 
> > T = TensorProductOfCrystals(*[C]*3) 
> > hw = [ a for a in T if a.e(1) == None ] 
> > sum( L.term( a.weight(), 1 ) for a in hw ) 
> > 
> > I would like to convince sage (in this simplified example) that these 
> are "the same". 
> > 
> > Thank you for your patience. 
> > 
> > On Saturday, November 23, 2013 7:28:26 AM UTC, Nicolas M. Thiery wrote: 
> > 
> >     On Fri, Nov 22, 2013 at 08:09:25AM -0800, Bruce wrote: 
> >     >    Here is the result of the first calculation (using the KR 
> crystal) and its 
> >     >    parent: 
> > 
> >     Please, not the result but the command (or a simplified version) 
> >     producing the result!  Otherwise one has to reconstruct the command 
> to 
> >     play with the objects :-) 
> > 
> >     Cheers, 
> >                                     Nicolas 
>

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