Langton's ant

Langton's ant, which wanders chaotically for about 10,000 steps before it builds a periodic highway.

• Name: langtons_ant
• Field: computer_science/automata
• Formalism: lattice dynamics
• References: Langton 1986

Factory

@register_model(
    field='computer_science/automata',
    tags=('lattice', 'ant', 'emergence'),
    references=('Langton 1986',),
    defaults={'until': 11000, 'dt': 100},
)
def langtons_ant(shape: Sequence[int] = (80, 80), *, heading: int = 0) -> System:
    """Return Langton's ant, which wanders chaotically for about 10,000 steps before it builds a periodic highway.

    Args:
        shape:
            The number of rows and columns of the torus.

        heading:
            The initial heading of the ant, 0 to 3 for north, east, south, and west.

    Returns:
        system:
            The model, with the colors `cells.color` and the ant `cells.ant`.

    Examples:
        >>> from skcomplex.models.computer_science.automata import langtons_ant
        >>> int((langtons_ant((9, 9)).elements[0].values['ant'] >= 0).sum())
        1
    """
    ant = np.full(tuple(shape), -1.0)
    ant[shape[0] // 2, shape[1] // 2] = heading
    return System(
        elements=[
            LatticeElement('cells', element=AntCellElement, space=LatticeSpace(tuple(shape)), values={'ant': ant}),
        ],
        interactions=[
            LocalRuleInteraction(
                'ant',
                target='cells',
                state=('color', 'ant'),
                rule=_ant_rule,
                neighborhood=VonNeumannNeighborhood(center=True),
                reads=('color', 'ant'),
            ),
        ],
    )

Components

class AntCellElement(Element):
    """Cell of Langton's ant: a color, and the heading of the ant on it or -1.

    The local rule of `langtons_ant` turns the ant right on a white cell and left on a black one, flips the cell's
    color, and moves the ant one cell forward.

    Args:
        label:
            The label of the cell or the lattice group.

        visual:
            How the element is drawn, or `None` for `default_visual_`.

        color:
            The initial color, 0 for white and 1 for black.

        ant:
            The initial heading of an ant on the cell, 0 to 3 for north, east, south, and west, or -1 for none.

    Examples:
        >>> from skcomplex.models.computer_science.automata import AntCellElement
        >>> AntCellElement('cell').ant
        -1
    """

    def __init__(
        self,
        label: str,
        visual: VisualSpec | None = None,
        *,
        color: Annotated[float, StateSpec(domain=FiniteEnumeratedSet([0, 1]))] = 0,
        ant: Annotated[float, StateSpec(domain=ZZ)] = -1,
    ) -> None:
        super().__init__(label, visual=visual)
        self.color = color
        self.ant = ant

class LocalRuleInteraction(Interaction):
    """Local rule of a cellular automaton, which sets the next value of every cell from its ordered neighbourhood.

    The rule is a table of the next value of every configuration of the neighbourhood, `TableSpec`, a rule of the sum
    of the neighbourhood, `TotalisticSpec`, a rule of the cell and the sum of its neighbours, `OuterTotalisticSpec`, an
    object whose `table()` returns a `TableSpec`, or a function. A function receives one array per neighbour of every
    read state, in neighbourhood order, with one value per cell, the uniform array `random` when the rule is stochastic,
    and the parameters of the bound group it names, and returns the next values of the states, one array per state.

    Args:
        label:
            The label of the interaction, unique among the parts of its system.

        target:
            The path of the group on the cells of a lattice, the nodes of a network, or a Cayley graph.

        state:
            The name of the state the rule sets, or a tuple of the names of the states it sets together.

        rule:
            The table, the totalistic rule, or the function.

        neighborhood:
            The ordered neighbourhood of every cell, such as `VonNeumannNeighborhood(center=True)`.

        reads:
            The names of the states whose neighbourhoods a function reads, or `None` for the states it sets.

        schedule:
            `'synchronous'`, `'random-sequential'`, `'random-site'`, `'checkerboard'`, or `'colored'`.

        stochastic:
            Whether a function receives the uniform random array `random`.

    Raises:
        ValidationError:
            The state or the read states are not names, or the neighbourhood is not a neighbourhood.

    Examples:
        >>> from skcomplex.core.interactions import LocalRuleInteraction
        >>> from skcomplex.core.spaces import VonNeumannNeighborhood
        >>> from skcomplex.specs import TotalisticSpec
        >>> parity = TotalisticSpec({1: 1, 3: 1})
        >>> around = VonNeumannNeighborhood(n_dim=1, center=True)
        >>> rule = LocalRuleInteraction('parity', target='cells', state='cell', rule=parity, neighborhood=around)
        >>> rule.check().schedule
        'synchronous'
    """

    def __init__(
        self,
        label: str,
        *,
        target: Annotated[str, RoleSpec()],
        state: str | tuple[str, ...],
        rule: object,
        neighborhood: BaseNeighborhood,
        reads: Sequence[str] | None = None,
        schedule: str = 'synchronous',
        stochastic: bool = False,
    ) -> None:
        super().__init__(label)
        self.target = target
        self.state = state
        self.rule = rule
        self.neighborhood = neighborhood
        self.reads = reads
        self.schedule = schedule
        self.stochastic = stochastic

    def _get_names(self) -> tuple[str, ...]:
        """Return the names of the states the rule sets."""
        return (self.state,) if isinstance(self.state, str) else tuple(self.state)

    def _check(self) -> None:
        """Raise an error for states that are not names, or a neighbourhood that is not one.

        Raises:
            ValidationError:
                The state or the read states are not names, or the neighbourhood is not a neighbourhood.
        """
        super()._check()
        names = [*self._get_names(), *(self.reads or ())]
        if not names or not all(isinstance(name, str) and name.isidentifier() for name in names):
            error_msg = f'The local rule {self.label!r} sets {self.state!r} and reads {self.reads!r}. Give state names.'
            raise ValidationError(error_msg)
        if not isinstance(self.neighborhood, BaseNeighborhood):
            error_msg = f'The neighbourhood of the local rule {self.label!r} is {self.neighborhood!r}. Give one.'
            raise ValidationError(error_msg)

    def _get_laws(self, namespace: SimpleNamespace) -> list[BaseLaw]:
        """Return the local rule law of the states of the target.

        Args:
            namespace:
                The namespace of the symbols the laws can use, with `namespace.target`.

        Returns:
            laws:
                The local rule law.
        """
        targets = tuple(getattr(self._get_member(namespace, 'target'), name) for name in self._get_names())
        reads = (
            None
            if self.reads is None
            else tuple(getattr(self._get_member(namespace, 'target'), name) for name in self.reads)
        )
        return [
            LocalRuleLaw(
                targets[0] if isinstance(self.state, str) else targets,
                self.neighborhood,
                self.rule,
                reads=reads,
                schedule=self.schedule,
                stochastic=self.stochastic,
                label=self.label,
            ),
        ]