Let g be an affine Lie algebra and g^L be its Langlands dual. It is
conjectured that g has a positive geometric crystal whose ultra-discretization
is isomorphic to the limit of certain coherent family of perfect crystals for
g^L. We prove that the ultra-discretization of the positive geometric crystal
for g = D_4^3 given by Igarashi and Nakashima is isomorphic to the limit of the
coherent family of perfect crystals for g^L= G_2^1 constructed recently by
Misra, Mohamad and Okado.
For a classical simple algebraic group $G$ we obtain the affirmative answer
for the conjecture in [8] that there exists an isomorphism between the
geometric crystal on the flag variety and the one on the unipotent subgroup
$U^-$.
We introduce an epsilon system on a geometric crystal of type $A_n$, which is
a certain set of rational functions with some conditions. We shall show that
there is a product structure and that it is invariant under the action of
tropical R maps.
We shall realize certain affine geometric crystal of type $D_4^{(3)}$
associated with the fundamental representation $W(\pi_1)$ explicitly . By its
explicit form, we see that it has a positive structure.
We present a one-to-one correspondence between the set of admissible pictures
and the Littlewood-Richardson crystals. As a simple consequence, we shall show
that the set of pictures does not depend on the choice of admissible orders.