Loop Crystals

class sage.categories.loop_crystals.KirillovReshetikhinCrystals(s=None)

Bases: sage.categories.category_singleton.Category_singleton

Category of Kirillov-Reshetikhin crystals.

class ElementMethods

Bases: object

energy_function()

Return the energy function of self.

Let $B$ be a KR crystal. Let $b^{\sharp}$ denote the unique element such that $\varphi(b^{\sharp}) = \ell \Lambda_0$ with $\ell = \min \{ \langle c, \varphi(b) \mid b \in B \}$. Let $u_B$ denote the maximal element of $B$. The energy of $b \in B$ is given by

$$D(b) = H(b \otimes b^{\sharp}) - H(u_B \otimes b^{\sharp}),$$

where $H$ is the local energy function.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['D',4,1], 2,1)
sage: for x in K.classically_highest_weight_vectors():
....:    x, x.energy_function()
([], 1)
([[1], [2]], 0)

sage: K = crystals.KirillovReshetikhin(['D',4,3], 1,2)
sage: for x in K.classically_highest_weight_vectors():
....:    x, x.energy_function()
([], 2)
([[1]], 1)
([[1, 1]], 0)

lusztig_involution()

Return the result of the classical Lusztig involution on self.

EXAMPLES:

sage: KRT = crystals.KirillovReshetikhin(['D',4,1], 2, 3, model='KR')
sage: mg = KRT.module_generators[1]
sage: mg.lusztig_involution()
[[-2, -2, 1], [-1, -1, 2]]
sage: elt = mg.f_string([2,1,3,2]); elt
[[3, -2, 1], [4, -1, 2]]
sage: elt.lusztig_involution()
[[-4, -2, 1], [-3, -1, 2]]

class ParentMethods

Bases: object

R_matrix(K)

Return the combinatorial $R$-matrix of self to K.

The combinatorial $R$-matrix is the affine crystal isomorphism $R : L \otimes K \to K \otimes L$ which maps $u_{L} \otimes u_K$ to $u_K \otimes u_{L}$, where $u_K$ is the unique element in $K = B^{r,s}$ of weight $s\Lambda_r - s c \Lambda_0$ (see maximal_vector()).

INPUT:

• self – a crystal $L$

• K – a Kirillov-Reshetikhin crystal of the same type as $L$

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',2,1],1,1)
sage: L = crystals.KirillovReshetikhin(['A',2,1],1,2)
sage: f = K.R_matrix(L)
sage: [[b,f(b)] for b in crystals.TensorProduct(K,L)]
[[[[[1]], [[1, 1]]], [[[1, 1]], [[1]]]],
 [[[[1]], [[1, 2]]], [[[1, 1]], [[2]]]],
 [[[[1]], [[2, 2]]], [[[1, 2]], [[2]]]],
 [[[[1]], [[1, 3]]], [[[1, 1]], [[3]]]],
 [[[[1]], [[2, 3]]], [[[1, 2]], [[3]]]],
 [[[[1]], [[3, 3]]], [[[1, 3]], [[3]]]],
 [[[[2]], [[1, 1]]], [[[1, 2]], [[1]]]],
 [[[[2]], [[1, 2]]], [[[2, 2]], [[1]]]],
 [[[[2]], [[2, 2]]], [[[2, 2]], [[2]]]],
 [[[[2]], [[1, 3]]], [[[2, 3]], [[1]]]],
 [[[[2]], [[2, 3]]], [[[2, 2]], [[3]]]],
 [[[[2]], [[3, 3]]], [[[2, 3]], [[3]]]],
 [[[[3]], [[1, 1]]], [[[1, 3]], [[1]]]],
 [[[[3]], [[1, 2]]], [[[1, 3]], [[2]]]],
 [[[[3]], [[2, 2]]], [[[2, 3]], [[2]]]],
 [[[[3]], [[1, 3]]], [[[3, 3]], [[1]]]],
 [[[[3]], [[2, 3]]], [[[3, 3]], [[2]]]],
 [[[[3]], [[3, 3]]], [[[3, 3]], [[3]]]]]

sage: K = crystals.KirillovReshetikhin(['D',4,1],1,1)
sage: L = crystals.KirillovReshetikhin(['D',4,1],2,1)
sage: f = K.R_matrix(L)
sage: T = crystals.TensorProduct(K,L)
sage: b = T( K(rows=[[1]]), L(rows=[]) )
sage: f(b)
[[[2], [-2]], [[1]]]

Alternatively, one can compute the combinatorial $R$-matrix using the isomorphism method of digraphs:

sage: K1 = crystals.KirillovReshetikhin(['A',2,1],1,1)
sage: K2 = crystals.KirillovReshetikhin(['A',2,1],2,1)
sage: T1 = crystals.TensorProduct(K1,K2)
sage: T2 = crystals.TensorProduct(K2,K1)
sage: T1.digraph().is_isomorphic(T2.digraph(), edge_labels=True, certificate=True) #todo: not implemented (see #10904 and #10549)
(True, {[[[1]], [[2], [3]]]: [[[1], [3]], [[2]]], [[[3]], [[2], [3]]]: [[[2], [3]], [[3]]],
[[[3]], [[1], [3]]]: [[[1], [3]], [[3]]], [[[1]], [[1], [3]]]: [[[1], [3]], [[1]]], [[[1]],
[[1], [2]]]: [[[1], [2]], [[1]]], [[[2]], [[1], [2]]]: [[[1], [2]], [[2]]], [[[3]],
[[1], [2]]]: [[[2], [3]], [[1]]], [[[2]], [[1], [3]]]: [[[1], [2]], [[3]]], [[[2]], [[2], [3]]]: [[[2], [3]], [[2]]]})

affinization()

Return the corresponding affinization crystal of self.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',2,1], 1, 1)
sage: K.affinization()
Affinization of Kirillov-Reshetikhin crystal of type ['A', 2, 1] with (r,s)=(1,1)

sage: K = crystals.KirillovReshetikhin(['A',2,1], 1, 1, model='KR')
sage: K.affinization()
Affinization of Kirillov-Reshetikhin tableaux of type ['A', 2, 1] and shape (1, 1)

b_sharp()

Return the element $b^{\sharp}$ of self.

Let $B$ be a KR crystal. The element $b^{\sharp}$ is the unique element such that $\varphi(b^{\sharp}) = \ell \Lambda_0$ with $\ell = \min \{ \langle c, \varphi(b) \rangle \mid b \in B \}$.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',6,2], 2,1)
sage: K.b_sharp()
[]
sage: K.b_sharp().Phi()
Lambda[0]

sage: K = crystals.KirillovReshetikhin(['C',3,1], 1,3)
sage: K.b_sharp()
[[-1]]
sage: K.b_sharp().Phi()
2*Lambda[0]

sage: K = crystals.KirillovReshetikhin(['D',6,2], 2,2)
sage: K.b_sharp() # long time
[]
sage: K.b_sharp().Phi() # long time
2*Lambda[0]

cardinality()

Return the cardinality of self.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['E',6,1], 1,1)
sage: K.cardinality()
27
sage: K = crystals.KirillovReshetikhin(['C',6,1], 4,3)
sage: K.cardinality()
4736732

classical_decomposition()

Return the classical decomposition of self.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',3,1], 2,2)
sage: K.classical_decomposition()
The crystal of tableaux of type ['A', 3] and shape(s) [[2, 2]]

classically_highest_weight_vectors()

Return the classically highest weight elements of self.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['E',6,1],1,1)
sage: K.classically_highest_weight_vectors()
([(1,)],)

is_perfect(ell=None)

Check if self is a perfect crystal of level ell.

A crystal $\mathcal{B}$ is perfect of level $\ell$ if:

1. $\mathcal{B}$ is isomorphic to the crystal graph of a finite-dimensional $U_q'(\mathfrak{g})$-module.

2. $\mathcal{B} \otimes \mathcal{B}$ is connected.

3. There exists a $\lambda\in X$, such that $\mathrm{wt}(\mathcal{B}) \subset \lambda + \sum_{i\in I} \ZZ_{\le 0} \alpha_i$ and there is a unique element in $\mathcal{B}$ of classical weight $\lambda$.

4. For all $b \in \mathcal{B}$, $\mathrm{level}(\varepsilon (b)) \geq \ell$.

5. For all $\Lambda$ dominant weights of level $\ell$, there exist unique elements $b_{\Lambda}, b^{\Lambda} \in \mathcal{B}$, such that $\varepsilon(b_{\Lambda}) = \Lambda = \varphi(b^{\Lambda})$.

Points (1)-(3) are known to hold. This method checks points (4) and (5).

If self is the Kirillov-Reshetikhin crystal $B^{r,s}$, then it was proven for non-exceptional types in [FOS2010] that it is perfect if and only if $s/c_r$ is an integer (where $c_r$ is a constant related to the type of the crystal).

It is conjectured this is true for all affine types.

INPUT:

• ell – (default: $s / c_r$) integer; the level

REFERENCES:

[FOS2010]

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',2,1], 1, 1)
sage: K.is_perfect()
True

sage: K = crystals.KirillovReshetikhin(['C',2,1], 1, 1)
sage: K.is_perfect()
False

sage: K = crystals.KirillovReshetikhin(['C',2,1], 1, 2)
sage: K.is_perfect()
True

sage: K = crystals.KirillovReshetikhin(['E',6,1], 1,3)
sage: K.is_perfect()
True

Todo

Implement a version for tensor products of KR crystals.

level()

Return the level of self when self is a perfect crystal.

See also

is_perfect()

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',2,1], 1, 1)
sage: K.level()
1
sage: K = crystals.KirillovReshetikhin(['C',2,1], 1, 2)
sage: K.level()
1
sage: K = crystals.KirillovReshetikhin(['D',4,1], 1, 3)
sage: K.level()
3

sage: K = crystals.KirillovReshetikhin(['C',2,1], 1, 1)
sage: K.level()
Traceback (most recent call last):
...
ValueError: this crystal is not perfect

local_energy_function(B)

Return the local energy function of self and B.

See LocalEnergyFunction for a definition.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',6,2], 2,1)
sage: Kp = crystals.KirillovReshetikhin(['A',6,2], 1,1)
sage: H = K.local_energy_function(Kp); H
Local energy function of
 Kirillov-Reshetikhin crystal of type ['BC', 3, 2] with (r,s)=(2,1)
tensor
 Kirillov-Reshetikhin crystal of type ['BC', 3, 2] with (r,s)=(1,1)

maximal_vector()

Return the unique element of classical weight $s \Lambda_r$ in self.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['C',2,1],1,2)
sage: K.maximal_vector()
[[1, 1]]
sage: K = crystals.KirillovReshetikhin(['E',6,1],1,1)
sage: K.maximal_vector()
[(1,)]

sage: K = crystals.KirillovReshetikhin(['D',4,1],2,1)
sage: K.maximal_vector()
[[1], [2]]

module_generator()

Return the unique module generator of classical weight $s \Lambda_r$ of the Kirillov-Reshetikhin crystal $B^{r,s}$.

EXAMPLES:

sage: La = RootSystem(['G',2,1]).weight_space().fundamental_weights()
sage: K = crystals.ProjectedLevelZeroLSPaths(La[1])
sage: K.module_generator()
(-Lambda[0] + Lambda[1],)

q_dimension(q=None, prec=None, use_product=False)

Return the $q$-dimension of self.

The $q$-dimension of a KR crystal is defined as the $q$-dimension of the underlying classical crystal.

EXAMPLES:

sage: KRC = crystals.KirillovReshetikhin(['A',2,1], 2,2)
sage: KRC.q_dimension()
q^4 + q^3 + 2*q^2 + q + 1
sage: KRC = crystals.KirillovReshetikhin(['D',4,1], 2,1)
sage: KRC.q_dimension()
q^10 + q^9 + 3*q^8 + 3*q^7 + 4*q^6 + 4*q^5 + 4*q^4 + 3*q^3 + 3*q^2 + q + 2

r()

Return the value $r$ in self written as $B^{r,s}$.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',3,1], 2,4)
sage: K.r()
2

s()

Return the value $s$ in self written as $B^{r,s}$.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',3,1], 2,4)
sage: K.s()
4

class TensorProducts(category, *args)

Bases: sage.categories.tensor.TensorProductsCategory

The category of tensor products of Kirillov-Reshetikhin crystals.

class ElementMethods

Bases: object

affine_grading()

Return the affine grading of self.

The affine grading is calculated by finding a path from self to a ground state path (using the helper method e_string_to_ground_state()) and counting the number of affine Kashiwara operators $e_0$ applied on the way.

OUTPUT: an integer

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',2,1],1,1)
sage: T = crystals.TensorProduct(K,K)
sage: t = T.module_generators[0]
sage: t.affine_grading()
1

sage: K = crystals.KirillovReshetikhin(['A',2,1],1,1)
sage: T = crystals.TensorProduct(K,K,K)
sage: hw = T.classically_highest_weight_vectors()
sage: for b in hw:
....:     print("{} {}".format(b, b.affine_grading()))
[[[1]], [[1]], [[1]]] 3
[[[2]], [[1]], [[1]]] 2
[[[1]], [[2]], [[1]]] 1
[[[3]], [[2]], [[1]]] 0

sage: K = crystals.KirillovReshetikhin(['C',2,1],1,1)
sage: T = crystals.TensorProduct(K,K,K)
sage: hw = T.classically_highest_weight_vectors()
sage: for b in hw:
....:     print("{} {}".format(b, b.affine_grading()))
[[[1]], [[1]], [[1]]] 2
[[[2]], [[1]], [[1]]] 1
[[[-1]], [[1]], [[1]]] 1
[[[1]], [[2]], [[1]]] 1
[[[-2]], [[2]], [[1]]] 0
[[[1]], [[-1]], [[1]]] 0

e_string_to_ground_state()

Return a string of integers in the index set $(i_1, \ldots, i_k)$ such that $e_{i_k} \cdots e_{i_1}$ of self is the ground state.

This method calculates a path from self to a ground state path using Demazure arrows as defined in Lemma 7.3 in [ST2011].

OUTPUT: a tuple of integers $(i_1, \ldots, i_k)$

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',2,1],1,1)
sage: T = crystals.TensorProduct(K,K)
sage: t = T.module_generators[0]
sage: t.e_string_to_ground_state()
(0, 2)

sage: K = crystals.KirillovReshetikhin(['C',2,1],1,1)
sage: T = crystals.TensorProduct(K,K)
sage: t = T.module_generators[0]; t
[[[1]], [[1]]]
sage: t.e_string_to_ground_state()
(0,)
sage: x = t.e(0)
sage: x.e_string_to_ground_state()
()
sage: y = t.f_string([1,2,1,1,0]); y
[[[2]], [[1]]]
sage: y.e_string_to_ground_state()
()

energy_function(algorithm=None)

Return the energy function of self.

ALGORITHM:

definition

Let $T$ be a tensor product of Kirillov-Reshetikhin crystals. Let $R_i$ and $H_i$ be the combinatorial $R$-matrix and local energy functions, respectively, acting on the $i$ and $i+1$ factors. Let $D_B$ be the energy function of a single Kirillov-Reshetikhin crystal. The energy function is given by

$$D = \sum_{j > i} H_i R_{i+1} R_{i+2} \cdots R_{j-1} + \sum_j D_B R_1 R_2 \cdots R_{j-1},$$

where $D_B$ acts on the rightmost factor.

grading

If self is an element of $T$, a tensor product of perfect crystals of the same level, then use the affine grading to determine the energy. Specifically, let $g$ denote the affine grading of self and $d$ the affine grading of the maximal vector in $T$. Then the energy of self is given by $d - g$.

For more details, see Theorem 7.5 in [ST2011].

INPUT:

• algorithm – (default: None) use one of the following algorithms to determine the energy function:

  • 'definition' - use the definition of the energy function;

  • 'grading' - use the affine grading;

  if not specified, then this uses 'grading' if all factors are perfect of the same level and otherwise this uses 'definition'

OUTPUT: an integer

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',2,1], 1, 1)
sage: T = crystals.TensorProduct(K,K,K)
sage: hw = T.classically_highest_weight_vectors()
sage: for b in hw:
....:     print("{} {}".format(b, b.energy_function()))
[[[1]], [[1]], [[1]]] 0
[[[2]], [[1]], [[1]]] 1
[[[1]], [[2]], [[1]]] 2
[[[3]], [[2]], [[1]]] 3

sage: K = crystals.KirillovReshetikhin(['C',2,1], 1, 2)
sage: T = crystals.TensorProduct(K,K)
sage: hw = T.classically_highest_weight_vectors()
sage: for b in hw:
....:     print("{} {}".format(b, b.energy_function()))
[[], []] 4
[[[1, 1]], []] 3
[[], [[1, 1]]] 1
[[[1, 1]], [[1, 1]]] 0
[[[1, 2]], [[1, 1]]] 1
[[[2, 2]], [[1, 1]]] 2
[[[-1, -1]], [[1, 1]]] 2
[[[1, -1]], [[1, 1]]] 2
[[[2, -1]], [[1, 1]]] 2

sage: K = crystals.KirillovReshetikhin(['C',2,1], 1, 1)
sage: T = crystals.TensorProduct(K)
sage: t = T.module_generators[0]
sage: t.energy_function('grading')
Traceback (most recent call last):
...
NotImplementedError: all crystals in the tensor product
 need to be perfect of the same level

class ParentMethods

Bases: object

cardinality()

Return the cardinality of self.

EXAMPLES:

sage: RC = RiggedConfigurations(['A', 3, 1], [[3, 2], [1, 2]])
sage: RC.cardinality()
100
sage: len(RC.list())
100

sage: RC = RiggedConfigurations(['E', 7, 1], [[1,1]])
sage: RC.cardinality()
134
sage: len(RC.list())
134

sage: RC = RiggedConfigurations(['B', 3, 1], [[2,2],[1,2]])
sage: RC.cardinality()
5130

classically_highest_weight_vectors()

Return the classically highest weight elements of self.

This works by using a backtracking algorithm since if $b_2 \otimes b_1$ is classically highest weight then $b_1$ is classically highest weight.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',2,1],1,1)
sage: T = crystals.TensorProduct(K,K,K)
sage: T.classically_highest_weight_vectors()
([[[1]], [[1]], [[1]]],
 [[[2]], [[1]], [[1]]],
 [[[1]], [[2]], [[1]]],
 [[[3]], [[2]], [[1]]])

maximal_vector()

Return the maximal vector of self.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',2,1],1,1)
sage: T = crystals.TensorProduct(K,K,K)
sage: T.maximal_vector()
[[[1]], [[1]], [[1]]]

one_dimensional_configuration_sum(q=None, group_components=True)

Compute the one-dimensional configuration sum of self.

INPUT:

• q – (default: None) a variable or None; if None, a variable $q$ is set in the code

• group_components – (default: True) boolean; if True, then the terms are grouped by classical component

The one-dimensional configuration sum is the sum of the weights of all elements in the crystal weighted by the energy function.

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['A',2,1],1,1)
sage: T = crystals.TensorProduct(K,K)
sage: T.one_dimensional_configuration_sum()
B[-2*Lambda[1] + 2*Lambda[2]] + (q+1)*B[-Lambda[1]]
 + (q+1)*B[Lambda[1] - Lambda[2]] + B[2*Lambda[1]]
 + B[-2*Lambda[2]] + (q+1)*B[Lambda[2]]
sage: R.<t> = ZZ[]
sage: T.one_dimensional_configuration_sum(t, False)
B[-2*Lambda[1] + 2*Lambda[2]] + (t+1)*B[-Lambda[1]]
 + (t+1)*B[Lambda[1] - Lambda[2]] + B[2*Lambda[1]]
 + B[-2*Lambda[2]] + (t+1)*B[Lambda[2]]

sage: R = RootSystem(['A',2,1])
sage: La = R.weight_space().basis()
sage: LS = crystals.ProjectedLevelZeroLSPaths(2*La[1])
sage: LS.one_dimensional_configuration_sum() == T.one_dimensional_configuration_sum() # long time
True

extra_super_categories()

EXAMPLES:

sage: from sage.categories.loop_crystals import KirillovReshetikhinCrystals
sage: KirillovReshetikhinCrystals().TensorProducts().extra_super_categories()
[Category of finite regular loop crystals]

super_categories()

EXAMPLES:

sage: from sage.categories.loop_crystals import KirillovReshetikhinCrystals
sage: KirillovReshetikhinCrystals().super_categories()
[Category of finite regular loop crystals]

class sage.categories.loop_crystals.LocalEnergyFunction(B, Bp, normalization=0)

Bases: sage.categories.map.Map

The local energy function.

Let $B$ and $B'$ be Kirillov-Reshetikhin crystals with maximal vectors $u_B$ and $u_{B'}$ respectively. The local energy function $H : B \otimes B' \to \ZZ$ is the function which satisfies

$$\begin{split}H(e_0(b \otimes b')) = H(b \otimes b') + \begin{cases} 1 & \text{if } i = 0 \text{ and LL}, \\ -1 & \text{if } i = 0 \text{ and RR}, \\ 0 & \text{otherwise,} \end{cases}\end{split}$$

where LL (resp. RR) denote $e_0$ acts on the left (resp. right) on both $b \otimes b'$ and $R(b \otimes b')$, and normalized by $H(u_B \otimes u_{B'}) = 0$.

INPUT:

• B – a Kirillov-Reshetikhin crystal

• Bp – a Kirillov-Reshetikhin crystal

• normalization – (default: 0) the normalization value

EXAMPLES:

sage: K = crystals.KirillovReshetikhin(['C',2,1], 1,2)
sage: K2 = crystals.KirillovReshetikhin(['C',2,1], 2,1)
sage: H = K.local_energy_function(K2)
sage: T = tensor([K, K2])
sage: hw = T.classically_highest_weight_vectors()
sage: for b in hw:
....:     b, H(b)
([[], [[1], [2]]], 1)
([[[1, 1]], [[1], [2]]], 0)
([[[2, -2]], [[1], [2]]], 1)
([[[1, -2]], [[1], [2]]], 1)

REFERENCES:

[KKMMNN1992]

class sage.categories.loop_crystals.LoopCrystals(s=None)

Bases: sage.categories.category_singleton.Category_singleton

The category of $U_q'(\mathfrak{g})$-crystals, where $\mathfrak{g}$ is of affine type.

The category is called loop crystals as we can also consider them as crystals corresponding to the loop algebra $\mathfrak{g}_0[t]$, where $\mathfrak{g}_0$ is the corresponding classical type.

EXAMPLES:

sage: from sage.categories.loop_crystals import LoopCrystals
sage: C = LoopCrystals()
sage: C
Category of loop crystals
sage: C.super_categories()
[Category of crystals]
sage: C.example()
Kirillov-Reshetikhin crystal of type ['A', 3, 1] with (r,s)=(1,1)

class ParentMethods

Bases: object

digraph(subset=None, index_set=None)

Return the DiGraph associated to self.

INPUT:

• subset – (optional) a subset of vertices for which the digraph should be constructed

• index_set – (optional) the index set to draw arrows

See also

sage.categories.crystals.Crystals.ParentMethods.digraph()

EXAMPLES:

sage: C = crystals.KirillovReshetikhin(['D',4,1], 2, 1)
sage: G = C.digraph()
sage: G.latex_options()  # optional - dot2tex
LaTeX options for Digraph on 29 vertices:
{...'edge_options': <function ... at ...>...}
sage: view(G, tightpage=True)  # optional - dot2tex graphviz, not tested (opens external window)

weight_lattice_realization()

Return the weight lattice realization used to express weights of elements in self.

The default is to use the non-extended affine weight lattice.

EXAMPLES:

sage: C = crystals.Letters(['A', 5])
sage: C.weight_lattice_realization()
Ambient space of the Root system of type ['A', 5]
sage: K = crystals.KirillovReshetikhin(['A',2,1], 1, 1)
sage: K.weight_lattice_realization()
Weight lattice of the Root system of type ['A', 2, 1]

example(n=3)

Return an example of Kirillov-Reshetikhin crystals, as per Category.example().

EXAMPLES:

sage: from sage.categories.loop_crystals import LoopCrystals
sage: B = LoopCrystals().example(); B
Kirillov-Reshetikhin crystal of type ['A', 3, 1] with (r,s)=(1,1)

super_categories()

EXAMPLES:

sage: from sage.categories.loop_crystals import LoopCrystals
sage: LoopCrystals().super_categories()
[Category of crystals]

class sage.categories.loop_crystals.RegularLoopCrystals(s=None)

Bases: sage.categories.category_singleton.Category_singleton

The category of regular $U_q'(\mathfrak{g})$-crystals, where $\mathfrak{g}$ is of affine type.

class ElementMethods

Bases: object

classical_weight()

Return the classical weight of self.

EXAMPLES:

sage: R = RootSystem(['A',2,1])
sage: La = R.weight_space().basis()
sage: LS = crystals.ProjectedLevelZeroLSPaths(2*La[1])
sage: hw = LS.classically_highest_weight_vectors()
sage: [(v.weight(), v.classical_weight()) for v in hw]
[(-2*Lambda[0] + 2*Lambda[1], (2, 0, 0)),
 (-Lambda[0] + Lambda[2], (1, 1, 0))]

super_categories()

EXAMPLES:

sage: from sage.categories.loop_crystals import RegularLoopCrystals
sage: RegularLoopCrystals().super_categories()
[Category of regular crystals,
 Category of loop crystals]