def _selfridge_conway(self, agents,
residue: List[CakeSlice]) -> CakeAllocation:
"""
Implements the Selfridge-Conway on the given agents and the cake residue, returning
an allocation of slices.
:param agents: agents to allocate among
:param residue: residue to allocate
:return: allocation of the residue.
"""
p1 = agents[0]
p2 = agents[1]
p3 = agents[2]
allocation = CakeAllocation(slice_equally(p1, 3, residue))
p2_slices_order = sorted(allocation.all_slices,
key=lambda s: s.value_according_to(p2),
reverse=True)
# if p2 thinks the two largest slices are equal in value, allocation preferred by order p3,p2,p1
if abs(p2_slices_order[0].value_according_to(p2) -
p2_slices_order[1].value_according_to(p2)) < 0.001:
for agent in [p3, p2, p1]:
favorite = find_favorite_slice(agent,
allocation.unallocated_slices)
allocation.allocate_slice(agent, favorite)
return allocation
# cut largest slice into 2, so that one part will be equal to the second largest
slice_a = p2_slices_order[0]
slice_b = p2_slices_order[1]
slice_c = p2_slices_order[2]
trimmings = slice_a.slice_to_value(
p2, p2_slices_order[1].value_according_to(p2))
slice_a1 = trimmings[0]
slice_a2 = trimmings[1]
allocation.set_slice_split(slice_a, trimmings)
# p3 chooses among the large slices
large_slices = [slice_a1, slice_b, slice_c]
favorite = find_favorite_slice(p3, large_slices)
allocation.allocate_slice(p3, favorite)
large_slices.remove(favorite)
# p2 chooses among the large slices
# if a1 was not chosen by p3, p2 must choose a1
if slice_a1 != favorite:
agent_pa = p2
agent_pb = p3
allocation.allocate_slice(p2, slice_a1)
large_slices.remove(slice_a1)
else:
agent_pa = p3
agent_pb = p2
favorite = find_favorite_slice(p2, large_slices)
allocation.allocate_slice(p2, favorite)
large_slices.remove(favorite)
# p1 gets the last large slice
allocation.allocate_slice(p1, large_slices.pop())
# pb slices a2 into 3 parts
a2_sliced_parts = slice_a2.slice_equally(agent_pb, 3)
# agent choose slices in order pa, p1, pb
for agent in [agent_pa, p1, agent_pb]:
favorite = find_favorite_slice(agent, a2_sliced_parts)
allocation.allocate_slice(agent, favorite)
return allocation
def _core(self,
cutter: Agent,
residue: List[CakeSlice],
agents: List[Agent],
exclude_from_competition: Agent = None) -> CakeAllocation:
"""
Runs the core protocol of "An Improved Envy-Free Cake Cutting Protocol for Four Agents".
Starts by having `cutter` cut the residue into 4 slices which they view as equal in value.
The preferences of the other agents are then explored. Agents whose first preference is not
conflicted with other agents receive their favorite slice.
If all the agents received their favorite slice, return. Otherwise, we start the competition phase.
For each of the non-cutter agents, we compare preferences.
Agent who:
- has not competition on the second preference, or
- has 1 competition on the second preference, the competing agent also considers the slice as their second
preference, and both have 1 competition for their first preference
will make a "2-mark" on the first preference, which is a mark that makes the left part of the slice
equal in value to the second preference.
Other agents make a "3-mark" on the second preference, which is a mark that markes the left part of that
preference equal in value to the third preference.
Now allocate the slices by the rightmost rule:
Find an agent which has made the rightmost mark on 2 slices. If one was found,
out of those 2 slices, cut them until the second rightmost mark on each slice. Said
agent will receive the preferred out of the two slices. The other slice is given to the
agent who made the second rightmost mark on the slice taken by the previous agent.
If there is no agent with rightmost marks on 2 slices, all the slices with marks are
cut until the second rightmost mark, and each is allocated to the agent who made the rightmost mark.
If any non-cutters remain that did not receive any slice yet, they are each given their preferred
slice, out of the remaining uncut slices, in arbitrary order.
Now the cutter is given the last unallocated complete slice, and the allocation
of slices is returned.
:param cutter: agent responsible for cutting
:param residue: remaining slices of the cake
:param agents: agents participating in the current allocation
:param exclude_from_competition: agent to exclude from the competition stage.
:return: an allocation of cake slices.
>>> a = PiecewiseConstantAgent([10, 10, 10], "test1")
>>> a2 = PiecewiseConstantAgent([10, 10, 10], "test2")
>>> a3 = PiecewiseConstantAgent([10, 10, 10], "test3")
>>> a4 = PiecewiseConstantAgent([10, 10, 10], "test4")
>>> s = CakeSlice(0, 3)
>>> algo = Algorithm([a, a2, a3, a4], logging.getLogger("test"))
>>> alloc = algo._core(a, [s], [a2, a3, a4])
>>> alloc.unallocated_slices
[]
>>> sorted([agent.name() for agent in alloc.agents_with_allocations])
['test1', 'test2', 'test3', 'test4']
>>> [alloc.get_allocation_for_agent(agent) for agent in [a, a2, a3, a4]]
[[(2.25,3)], [(0.75,1.5)], [(0,0.75)], [(1.5,2.25)]]
"""
active_agents = exclude_from_list(agents, [cutter])
self._logger.info(
"Starting core with cutter {} and agents {} on residue {}".format(
cutter.name(),
', '.join([agent.name() for agent in active_agents]),
str(residue)))
# residue may not be a complete slice
# cutter slices into 4
slices = slice_equally(cutter, 4, residue)
self._logger.info("Residue sliced into {}".format(str(slices)))
preferences = get_preferences_for_agents(active_agents, slices)
allocation = CakeAllocation(slices)
satisfied_agents = []
for agent in active_agents:
preference = preferences.get_preference_for_agent(agent)
favorite = preference[0]
favorite_conflicts_first, _ = preferences \
.find_agents_with_preference_for(favorite,
exclude_agents=[agent, exclude_from_competition])
# line 8 if, not talking about lack of conflict for primary slice...
if len(favorite_conflicts_first) == 0:
allocation.allocate_slice(agent, favorite)
satisfied_agents.append(agent)
self._logger.info(
"{} has preference {} with no conflicts, allocating".
format(agent.name(), favorite))
else:
self._logger.info(
"{} has preference {} with conflicts, not allocating".
format(agent.name(), favorite))
for agent in satisfied_agents:
active_agents.remove(agent)
if len(active_agents) == 0:
self._logger.info(
"all agents satisfied, allocating {} to cutter {}".format(
str(allocation.free_complete_slices[0]), cutter.name()))
allocation.allocate_slice(cutter,
allocation.free_complete_slices[0])
self._logger.info("core finished with {}".format(', '.join(
"{}: {}".format(
agent.name(),
str(allocation.get_allocation_for_agent(agent)))
for agent in allocation.agents_with_allocations)))
return allocation
# Conflict
# do marking
exclude = list(satisfied_agents)
exclude.append(exclude_from_competition)
self._logger.info("Starting conflict handling, excluding {}".format(
', '.join([agent.name() for agent in filter(None, exclude)])))
for agent in exclude_from_list(active_agents,
[exclude_from_competition]):
slice, mark = mark_by_preferences(agent, preferences,
allocation.marking, exclude)
self._logger.info("{} made mark at {} on slice {}".format(
agent.name(), str(mark), str(slice)))
# Allocate by rightmost rule
self._logger.info("Starting allocation by rightmost rule")
agents_to_rightmost_marked_slices = allocation.marking.rightmost_marks_by_agents(
)
allocated = False
for agent, slices in agents_to_rightmost_marked_slices.items():
if len(slices) != 2:
continue
self._logger.info("{} has rightmost mark on 2 slices {}".format(
agent.name(), str(slices)))
agents_to_allocated, sliced = allocate_by_rightmost_to_agent(
agent, slices, allocation, allocation.marking)
self._logger.info("slices cut into {}".format(str(sliced)))
self._logger.info("allocated {}".format(', '.join([
'{}: {}'.format(agent.name(), str(slice))
for agent, slice in agents_to_allocated.items()
])))
allocated = True
break
if not allocated:
self._logger.info("No agent with rightmost mark on 2 slices")
agents_to_allocated, sliced = allocate_all_partials_by_marks(
allocation, allocation.marking)
self._logger.info("slices cut into {}".format(str(sliced)))
self._logger.info("allocated {}".format(', '.join([
'{}: {}'.format(agent.name(), str(slice))
for agent, slice in agents_to_allocated.items()
])))
# if any non-cutters not given any slices
# each should choose favorite un-allocated complete slice
for agent in exclude_from_list(active_agents,
[exclude_from_competition]):
if agent not in allocation.agents_with_allocations:
favorite = find_favorite_slice(agent,
allocation.free_complete_slices)
allocation.allocate_slice(agent, favorite)
self._logger.info(
"{} has not received slice yet, chose and received {}".
format(agent.name(), str(favorite)))
# cutter given remaining un-allocated complete slice
self._logger.info("cutter receives {}".format(
str(allocation.free_complete_slices[0])))
allocation.allocate_slice(cutter, allocation.free_complete_slices[0])
self._logger.info("core finished with {}".format(', '.join(
"{}: {}".format(agent.name(),
str(allocation.get_allocation_for_agent(agent)))
for agent in allocation.agents_with_allocations)))
return allocation
def _correction(self, cutter: Agent, allocation: CakeAllocation,
total_allocation: CakeAllocation):
"""
Runs the correction protocol of "An Improved Envy-Free Cake Cutting Protocol for Four Agents".
Define A and B as the agents who made 2 marks on the allocated insignificant slice, where
A is the one who received that allocation.
Transfer the slice to B.
If there are no more partial slices (other than the insignificant slice), agents
C, A and D are allocated their favorite slices out of all the slices in the allocation,
in order.
Otherwise if there is another partial slice, let E be the agent who made the rightmost mark on
it other than B.
Allocate that slice to E.
The remaining non-cutter chooses their favorite out of the 2 remaining slices and receives it.
The cutter receives the last slice.
:param cutter: cutter of the allocation to fix
:param allocation: allocation to fix
:param total_allocation: the complete state of the cake
:return: void
>>> a = PiecewiseConstantAgent([10, 10, 10], "test1")
>>> a2 = PiecewiseConstantAgent([10, 10, 10], "test2")
>>> a3 = PiecewiseConstantAgent([10, 10, 10], "test3")
>>> a4 = PiecewiseConstantAgent([10, 10, 10], "test4")
>>> s = CakeSlice(0,0.75)
>>> s2 = CakeSlice(0.75,1.5)
>>> s3 = CakeSlice(1.5,2)
>>> s4 = CakeSlice(2,2.25)
>>> s5 = CakeSlice(2.25,3)
>>> algo = Algorithm([a, a2, a3, a4, s5], logging.getLogger("test"))
>>> alloc = CakeAllocation([s, s2, s3, s4, s5])
>>> alloc.allocate_slice(a, s)
>>> alloc.allocate_slice(a2, s2)
>>> alloc.allocate_slice(a3, s3)
>>> alloc.allocate_slice(a4, s4)
>>> sorted([agent.name() for agent in alloc.agents_with_allocations])
['test1', 'test2', 'test3', 'test4']
>>> m = alloc.marking.mark(a3, s4, 2)
>>> m = alloc.marking.mark(a3, s4, 1)
>>> algo._correction(s, alloc, alloc)
>>> alloc.unallocated_slices
[(2.25,3)]
>>> sorted([agent.name() for agent in alloc.agents_with_allocations])
['test2', 'test3']
>>> [alloc.get_allocation_for_agent(agent) for agent in [a, a2, a3, a4]]
[[], [(0,0.75), (0.75,1.5)], [(1.5,2), (2,2.25)], []]
"""
agent_with_insignificant = allocation.try_get_agent_with_insignificant_slice(
)
insignificant_slice = allocation.get_insignificant_slice(
agent_with_insignificant)
marks = allocation.marking.marks_on_slice(insignificant_slice)
self._logger.info("{} has insignificant {}, with marks {}".format(
agent_with_insignificant.name(), str(insignificant_slice),
str([mark[1] for mark in marks])))
if len(marks) != 2:
raise ValueError("Slice should have 2 marks")
# find insignificant slice
# A, B agents who marked that slice
# B is allocated the slice
agent_a = agent_with_insignificant
agent_b = [mark[0] for mark in marks if mark[0] != agent_a][0]
self._logger.info("{} is allocated insignificant".format(
agent_b.name()))
total_allocation.allocate_slice(agent_b, insignificant_slice)
remaining_agents = exclude_from_list(self._agents, [agent_a, agent_b])
agent_c = remaining_agents[0]
agent_d = remaining_agents[1]
# if no other slice is marked
# agents choose fav by C, A, D
# only the insignificant slice remains
if len(allocation.partial_slices) <= 1:
self._logger.info("no other partial slices")
for agent in [agent_c, agent_a, agent_d]:
if len(allocation.all_slices) > 0:
favorite = find_favorite_slice(agent,
allocation.all_slices)
total_allocation.allocate_slice(agent, favorite)
self._logger.info("{} choose and received {}".format(
agent.name(), str(favorite)))
self._logger.info("correction finished with {}".format(', '.join(
"{}: {}".format(
agent.name(),
str(allocation.get_allocation_for_agent(agent)))
for agent in allocation.agents_with_allocations)))
# else
# find rightmost mark not made by B on the other partial piece
# E = agent who made it
# E is allocated partial piece
# last non-cutter chooses their favorite among 2 complete slices
# the cutter is allocated the remaining piece
else:
other_slice = exclude_from_list(allocation.partial_slices,
[insignificant_slice])[0]
self._logger.info("{} is the other partial slice")
agent_e, mark_made = [
(agent, mark)
for agent, mark in allocation.marking.marks_on_slice(
other_slice) if agent != agent_b
][0]
self._logger.info(
"{} made mark {} on slice and receives it".format(
agent_e.name(), str(mark_made)))
total_allocation.allocate_slice(agent_e, other_slice)
last_non_cutter = exclude_from_list(self._agents,
[cutter, agent_e, agent_b])[0]
favorite = find_favorite_slice(last_non_cutter[0],
allocation.free_complete_slices)
self._logger.info(
"{} last non cutter choose and received {}".format(
last_non_cutter.name, str(favorite)))
total_allocation.allocate_slice(last_non_cutter, favorite)
self._logger.info("{} (cutter) receives {}".format(
cutter.name(), str(allocation.free_complete_slices[0])))
total_allocation.allocate_slice(cutter,
allocation.free_complete_slices[0])
self._logger.info("correction finished with {}".format(', '.join(
"{}: {}".format(
agent.name(),
str(allocation.get_allocation_for_agent(agent)))
for agent in allocation.agents_with_allocations)))
def allocate_by_rightmost_to_agent(
agent: Agent, marked_slices: List[CakeSlice],
allocation: CakeAllocation, marking: Marking
) -> Tuple[Dict[Agent, CakeSlice], List[List[CakeSlice]]]:
"""
Allocates slices by the rightmost rule, as described by envy-free algorithm's main
protocol line 15: `agent` receives their preferred slice out of two slices
where they made the rightmost mark, while the agent who made the second-rightmost
mark on the preferred slice of `agent`, receives the second marked slice until
its second-rightmost mark.
Let's define `agent` who made the rightmost mark, on two slices (s1, s2).
Each slice (of s1,s2) will have 2 marks at the least. The slices
are split into to parts each at the location of the second-rightmost mark
(s11 {second-rightmost mark} s12), (s21 {second-rightmost mark} s22).
Define a as `agent`'s preferred slice out of s11 and s21, and b the other slice.
`agent` is receives that slice. The agent who made the second-rightmost mark on slice
a, receives slice b.
:param agent: agent with 2 rightmost marks, one on each slice
:param marked_slices: slices marked by agent
:param allocation: the current allocation scope
:param marking: the marking context
:return: a tuple composed of a dict mapping agent to slice received, and a list of slices made
>>> s = CakeSlice(0, 1)
>>> s2 = CakeSlice(1, 1.5)
>>> s3 = CakeSlice(1.7, 2)
>>> a = PiecewiseConstantAgent([10, 10, 10], "agent")
>>> a2 = PiecewiseConstantAgent([10, 10, 10], "agent2")
>>> marking = Marking()
>>> m = marking.mark(a, s, 10)
>>> m = marking.mark(a, s2, 5)
>>> m = marking.mark(a2, s, 5)
>>> m = marking.mark(a2, s2, 2.5)
>>> alloc = CakeAllocation([s, s2, s3])
>>> allocated, sliced = allocate_by_rightmost_to_agent(a, [s, s2, s3], alloc, marking)
>>> sliced
[[(0,0.5), (0.5,1)], [(1,1.25), (1.25,1.5)]]
>>> {agent.name(): slice for agent, slice in allocated.items()}
{'agent': (0,0.5), 'agent2': (1,1.25)}
"""
second_rightmost1_agent, second_rightmost1_pos = marking.second_rightmost_mark(
marked_slices[0])
second_rightmost2_agent, second_rightmost2_pos = marking.second_rightmost_mark(
marked_slices[1])
sliced1 = marked_slices[0].slice_at(second_rightmost1_pos)
sliced2 = marked_slices[1].slice_at(second_rightmost2_pos)
allocation.set_slice_split(marked_slices[0], list(sliced1))
allocation.set_slice_split(marked_slices[1], list(sliced2))
slice_option1 = sliced1[0]
slice_option2 = sliced2[0]
favorite = find_favorite_slice(agent, [slice_option1, slice_option2])
marking_agent_on_fav = second_rightmost1_agent if favorite == slice_option1 else second_rightmost2_agent
other_slice = slice_option1 if favorite == slice_option2 else slice_option2
allocation.allocate_slice(agent, favorite)
allocation.allocate_slice(marking_agent_on_fav, other_slice)
return {
agent: favorite,
marking_agent_on_fav: other_slice
}, [sliced1, sliced2]