Implement cayley_graph method for Artin groups

Added a method to return the Cayley graph of Artin groups, requiring elements to be specified due to their infinite nature.

src/sage/groups/artin.py

@@ -710,6 +710,47 @@ def as_permutation_group(self):
         """
         raise ValueError("the group is infinite")
 
+    def cayley_graph(self, side='right', simple=False, elements=None,
+                     generators=None, connecting_set=None):
+        r"""
+        Return the Cayley graph of ``self``.
+
+        Since Artin groups are infinite, this method requires ``elements``
+        to be specified. It uses the generic semigroup Cayley graph
+        implementation.
+
+        INPUT:
+
+        - ``side`` -- ``'left'``, ``'right'``, or ``'twosided'``:
+          the side on which the generators act (default: ``'right'``)
+        - ``simple`` -- boolean (default: ``False``); if ``True``, returns
+          a simple graph (no loops, no labels, no multiple edges)
+        - ``generators`` -- list, tuple, or family of elements
+          of ``self`` (default: ``self.gens()``)
+        - ``connecting_set`` -- alias for ``generators``; deprecated
+        - ``elements`` -- list (or iterable) of elements of ``self``
+          (required for infinite groups)
+
+        OUTPUT: :class:`DiGraph`
+
+        EXAMPLES::
+
+            sage: def ball(group, radius):
+            ....:     ret = set()
+            ....:     ret.add(group.one())
+            ....:     for length in range(1, radius):
+            ....:         for w in Words(alphabet=group.gens(), length=length):
+            ....:              ret.add(prod(w))
+            ....:     return ret
+            sage: A = ArtinGroup(['A',2])                                               # needs sage.rings.number_field
+            sage: GA = A.cayley_graph(elements=ball(A, 4), generators=A.gens()); GA     # needs sage.combinat sage.graphs sage.rings.number_field
+            Digraph on 14 vertices
+        """
+        from sage.categories.semigroups import Semigroups
+        return Semigroups().ParentMethods.cayley_graph(
+            self, side=side, simple=simple, elements=elements,
+            generators=generators, connecting_set=connecting_set)
+
     def coxeter_type(self):
         """
         Return the Coxeter type of ``self``.