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C HA P T E R 2
Ol i v e r S c h u l t e
Intelligent Agents

Outline
Artificial Intelligence a modern approach
2
 Agents and environments
 Rationality
 PEAS (Performance measure, Environment,
Actuators, Sensors)
 Environment types
 Agent types

3
The PEAS Model

Agents
4
• An agent is anything that can be viewed as
perceiving its environment through sensors and
acting upon that environment through actuators
• Human agent:
– eyes, ears, and other organs for sensors;
– hands, legs, mouth, and other body parts for actuators
• Robotic agent:
– cameras and infrared range finders for sensors
– various motors for actuators

Agents and environments
5
• The agent function maps from percept histories to
actions:
• [f: P*  A]
• The agent program runs on the physical architecture to
produce f
• agent = architecture + program

Vacuum-cleaner world
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 Percepts: location and contents, e.g., [A,Dirty]
 Actions: Left, Right, Suck, NoOp
 Agent’s function  look-up table
 For many agents this is a very large table
Demo With Open Source Code

7
Multiple Choice Question (not graded)
A rational agent
1. finds a correct solution every time.
2. achieves optimal performance every time.
3. achieves the best performance on average.
4. achieves the best worst-case performance.
Pick one.

Rational agents
8
• Rationality
– Performance measuring success
– Agents prior knowledge of environment
– Actions that agent can perform
– Agent’s percept sequence to date
• Rational Agent: For each possible percept sequence, a
rational agent should select an action that is expected to
maximize its performance measure, given the evidence
provided by the percept sequence and whatever built-in
knowledge the agent has.
• See File: intro-choice.doc
•

Rationality
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 Rational is different from omniscience
 Percepts may not supply all relevant information
 E.g., in card game, don’t know cards of others.
 Rational is different from being perfect
 Rationality maximizes expected outcome while perfection
maximizes actual outcome.

Autonomy in Agents
 Extremes
 No autonomy – ignores environment/data
 Complete autonomy – must act randomly/no program
 Example: baby learning to crawl
 Ideal: design agents to have some autonomy
 Possibly become more autonomous with experience
The autonomy of an agent is the extent to which its
behaviour is determined by its own experience,
rather than knowledge of designer.

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Multiple Choice Question
PEAS stands for
1. green vegetables.
2. Peace, Environment, Action, Service
3. Performance, Environment, Agent, Search.
4. Performance, Environment, Actuators, Sensors.
Check one.

PEAS
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• PEAS: Performance measure, Environment,
Actuators, Sensors.
• Must first specify the setting for intelligent agent
design
• Consider, e.g., the task of designing an automated
taxi driver:
– Performance measure: Safe, fast, legal, comfortable trip,
maximize profits
– Environment: Roads, other traffic, pedestrians, customers.
– Actuators: Steering wheel, accelerator, brake, signal, horn.
– Sensors: Cameras, sonar, speedometer, GPS, odometer,
engine sensors, keyboard

PEAS
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 Agent: Part-picking robot
 Performance measure: Percentage of parts in correct
bins
 Environment: Conveyor belt with parts, bins
 Actuators: Jointed arm and hand
 Sensors: Camera, joint angle sensors

PEAS
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 Agent: Interactive English tutor
 Performance measure: Maximize student's score on
test
 Environment: Set of students
 Actuators: Screen display (exercises, suggestions,
corrections)
 Sensors: Keyboard

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Environments

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In an episodic environment
1. outcomes do not depend on action history.
2. outcomes do depend on action history.
3. The environment does not change while the agent
is planning.
4. Other agents are involved in the episode.
Check one.

Environment types
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• Fully observable (vs. partially observable)
• Deterministic (vs. stochastic)
• Episodic (vs. sequential)
• Static (vs. dynamic)
• Discrete (vs. continuous)
• Single agent (vs. multiagent).

Fully observable (vs. partially observable)
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 Is everything an agent requires to choose its actions
available to it via its sensors?
 If so, the environment is fully accessible
 If not, parts of the environment are inaccessible
 Agent must make informed guesses about world.
Cross Word Backgammon Taxi driver Part picking robot
Poker Image analysis
Fully Fully Fully
Partially
Partially Partially

Deterministic (vs. stochastic)
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 Does the change in world state depend only on
current state and agent’s action?
 Non-deterministic environments
 Have aspects beyond the control of the agent
 Utility functions have to guess at changes in world
Cross Word Backgammon Taxi driver Part
Deterministic Deterministic
Stochastic
Stochastic
Stochastic Stochastic

Episodic (vs. sequential):
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 Is the choice of current action
 Dependent on previous actions?
 If not, then the environment is episodic
 In sequential environments:
 Agent has to plan ahead:
 Current choice will affect future actions
Sequential
Sequential
Sequential
Sequential Episodic Episodic

Static (vs. dynamic):
22
 Static environments don’t change
 While the agent is deliberating over what to do
 Dynamic environments do change
 So agent should/could consult the world when choosing actions
 Semidynamic: If the environment itself does not change
with the passage of time but the agent's performance
score does.
Static Static Static Dynamic
Dynamic Semi
Another example: off-line route planning vs. on-board
navigation system

Discrete (vs. continuous)
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 A limited number of distinct, clearly defined percepts and
actions vs. a range of values (continuous)
Discrete Discrete Discrete Conti Conti Conti

Single agent (vs. multiagent):
24
 An agent operating by itself in an environment vs.
there are many agents working together
Single Single Single
Multi
Multi
Multi

Summary.
Observable Deterministic Episodic Static Discrete Agents
Cross Word Fully Deterministic Sequential Static Discrete Single
Poker Fully Stochastic Sequential Static Discrete Multi
Backgammon Partially Stochastic Sequential Static Discrete Multi
Taxi driver Partially Stochastic Sequential Dynamic Conti Multi
Part picking
robot
Partially Stochastic Episodic Dynamic Conti Single
Image
analysis
Fully Deterministic Episodic Semi Conti Single

27
Agents

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A goal-based agent
1. uses reflexes to reach a goal.
2. maximizes average performance.
3. selects actions to reach a goal given sensory input.
4. learns from its experience.
Select one.

Agent types
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 Four basic types in order of increasing generality:
 Simple reflex agents
 Reflex agents with state/model
 Goal-based agents
 Utility-based agents
 All these can be turned into learning agents

Simple reflex agents
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Simple reflex agents
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 Simple but very limited intelligence.
 Action does not depend on percept history, only on
current percept.
 Thermostat.
Therefore no memory requirements.
 Infinite loops
 Suppose vacuum cleaner does not observe location. What
do you do given location = clean? Left on A or right on B -
> infinite loop.
 Fly buzzing around window or light.
 Possible Solution: Randomize action.

States: Beyond Reflexes
• Recall the agent function that maps from percept histories
to actions:
[f: P*  A]
 An agent program can implement an agent function by
maintaining an internal state.
 The internal state can contain information about the state
of the external environment.
 The state depends on the history of percepts and on the
history of actions taken:
[f: P*, A* S A] where S is the set of states.
32

Model-based reflex agents
34
 Know how world evolves
 Overtaking car gets closer from
behind
 How agents actions affect the
world
 Wheel turned clockwise takes you
right
 Model based agents update their
state

Goal-based agents
35
• knowing state and environment? Enough?
– Taxi can go left, right, straight
• Have a goal
 A destination to get to
 Uses knowledge about a goal to guide its actions
 E.g., Search, planning

Goal-based agents
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• Reflex agent breaks when it sees brake lights. Goal based agent
reasons
– Brake light -> car in front is stopping -> I should stop -> I should use brake

Utility-based agents
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 Goals are not always enough
 Many action sequences get taxi to destination
 Consider other things. How fast, how safe…..
 A utility function maps a state onto a real number
which describes the associated degree of
“happiness”, “goodness”, “success”.
 Where does the utility measure come from?
 Economics: money.
 Biology: number of offspring.
 Your life?

Utility-based agents
38

Learning agents
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 Performance element is
what was previously the
whole agent
 Input sensor
 Output action
 Learning element
 Modifies performance
element.

Learning agents (Taxi driver)
 Performance element
 How it currently drives
 Taxi driver Makes quick left turn across 3 lanes
 Critics observe shocking language by passenger and other drivers
and informs bad action
 Learning element tries to modify performance elements for future
 Problem generator suggests experiment: try out something called
Brakes on different Road conditions
 Exploration vs. Exploitation
 Learning experience can be costly in the short run
 shocking language from other drivers
 Less tip
 Fewer passengers
41

The Big Picture: AI for Model-Based Agents
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Action
Learning
Knowledge
Logic
Probability
Heuristics
Inference
Planning
Decision Theory
Game Theory
Reinforcement
Learning
Machine Learning
Statistics

The Picture for Reflex-Based Agents
43
Action
Learning
Reinforcement
Learning
• Studied in AI, Cybernetics, Control Theory, Biology,
Psychology.

Discussion Question
 Model-based behaviour has a large overhead.
 Our large brains are very expensive from an
evolutionary point of view.
 Why would it be worthwhile to base behaviour on a
model rather than “hard-code” it?
 For what types of organisms in what type of
environments?
 What kind of agent is the Dyson cleaner?
44

Summary
 Agents can be described by their PEAS.
 Environments can be described by several key properties:
64 Environment Types.
 A rational agent maximizes the performance measure for
their PEAS.
 The performance measure depends on the agent
function.
 The agent program implements the agent function.
 3 main architectures for agent programs.
 In this course we will look at some of the common and
useful combinations of environment/agent architecture.
45

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