Artificial Intelligence

Artificial Intelligence
Tutor:
Engr. Sander
Ali

Definition of an Agent
Anything/entity that can be viewed as
perceiving its environment through
sensors and acting upon the
environment through effectors.
Examples
 A Human Agent
 A Robotic Agent

Sensors/Percepts and Effectors/Actions
 Humans
◦ Sensors: Eyes (vision), ears (hearing), skin (touch), tongue
(gustation), nose (olfaction), neuromuscular system
(proprioception)
◦ Percepts:
 At the lowest level – electrical signals from these sensors
 After preprocessing – objects in the visual field (location,
textures, colors, …), auditory streams (pitch, loudness,
direction), …
◦ Effectors: limbs, digits, eyes, tongue, …
◦ Actions: lift a finger, turn left, walk, run, carry an object, …
 Robot
◦ Sensors: camera, infrared range finders,
◦ Effectors: motors
Percepts and actions need to be carefully defined, possibly at
different levels of abstraction

What is Intelligent Agent?
Software entities that carryout some set
of operations on behalf of a user or
another program with some degree of
independence or autonomy, and so
doing employ some knowledge or
representation of a user’s goals or
desires.

Description of an Agent
 An intelligent agent perceives its environment via
sensors and acts rationally upon that environment with
its effectors.
 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
Main components
– Perception (sensors)
– Reasoning/cognition
– Action (actuators)

Vacuum-cleaner world
 Percepts: location and contents, e.g.,
[A,Dirty]
 Actions: Left, Right, Suck, NoOp

Possible Properties
 Agents are autonomous – they act on behalf of the
user
 Agents can adapt to changes in the environment
 Agents not only act reactively, but sometimes also
proactively
 Agents have social ability – they communicate with
the user, the system, and other agents as required
 Agents also cooperate with other agents to carry out
more complex tasks than they themselves can handle
 Agents migrate from one system to another to
access remote resources or even to meet other
agents

PEAS
 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
◦ Environment
◦ Actuators
◦ Sensors

PEAS
 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, engine
sensors, keyboard
◦

PEAS
 Agent: Medical diagnosis system
 Performance measure: Healthy
patient, minimize costs, lawsuits
 Environment: Patient, hospital, staff
 Actuators: Screen display (questions,
tests, diagnoses, treatments, referrals)

 Sensors: Keyboard (entry of
symptoms, findings, patient's
answers)

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

Examples of agent types and their PEAS description
PEAS: Performance Measure, Environment, Actuators,
sensorsAgent type P E A S
Medical
Diagnosis
System
Healthy patient,
minimize costs,
lawsuits
Patient,
Hospital Staff
Display
questions, tests,
diagnoses,
treatments,
referrals
Keyboard entry
of symptoms,
findings, patient's
Answers.
Interactive
English Tutor
Maximize
student's score
on test.
Set of
students,
testing agency.
Display
exercises,
suggestions,
corrections
Typed words.
Satellite Image
Analysis
System
Correct
categorization
Downlink from
orbiting
satellite
Display
categorization of
scene.
Colour pixel
arrays.
Refinery
Controller
Maximize purity,
yield, safety
Refinery,
operators
Valves, pumps,
heaters, displays
Temperature,
pressure,
chemical sensors
Taxi Driver Safe: fast, legal,
comfortable trip,
maximize profits
Roads, other
traffic,
pedestrians,
customers
Steering,
accelerator,
brake, signal,
horn, display.
Cameras, sonar,
speedometer,
GPS, odometer,
accelerometer,
engine sensors,
keyboard.

Home Work
For each of the following agents, develop a
PEAS description of the task environment:
a. Robot soccer player;
b. Internet book-shopping agent;
c. Autonomous Mars rover;
d. Mathematician's theorem-proving
assistant.

Properties of Environments
1. Fully observable/Partially observable.
 If an agent’s sensors give it access to the complete state of the
environment needed to choose an action, the environment is fully
observable.
 Such environments are convenient, since the agent is freed from
the task of keeping track of the changes in the environment.
2. Deterministic/Stochastic.
 An environment is deterministic if the next state of the
environment is completely determined by the current state of the
environment and the action of the agent; in a stochastic
environment, there are multiple, unpredictable outcomes
 In a fully observable, deterministic environment, the agent need
not deal with uncertainty.

3. Episodic/Sequential.
 An episodic environment means that subsequent episodes do
not depend on what actions occurred in previous episodes.
 In a sequential environment, the agent engages in a series of
connected episodes.
 Such environments do not require the agent to plan ahead.
4. Static/Dynamic.
 A static environment does not change while the agent is
thinking.
 The passage of time as an agent deliberates is irrelevant.
 The agent doesn’t need to observe the world during deliberation.
 If the environment can change while an agent is deliberating,
then we say the environment is dynamic for the agent.
 If the environment does not change with the passage of time but
the agent’s performance score does, then we say the
environment is semi-dynamic.

5. Discrete/Continuous.
◦ If the number of distinct percepts and actions is
limited, the environment is discrete, otherwise it is
continuous.
6. Single-agent/Multi-agent.
◦ If the environment contains other intelligent agents,
the agent needs to be concerned about strategic,
game-theoretic aspects of the environment (for either
cooperative or competitive agents)
◦ Most engineering environments don’t have multi-agent
properties, whereas most social and economic
systems get their complexity from the interactions of
(more or less) rational agents.

Environment Properties - Examples
Fully
observabl
e?
Deterministic? Episodic? Static
?
Discrete? Single
agent?
Solitaire No Yes Yes Yes Yes Yes
Backgammo
n
Yes No No Yes Yes No
Taxi driving No No No No No No
Internet
shopping
No No No No Yes No
Medical
diagnosis
No No No No No Yes
→ Lots of real-world domains fall into the hardest case!

Basic Agents Types
1. Table-driven agents
use a percept sequence/action table in memory to find the next
action. They are implemented by a (large) lookup table.
2. Simple reflex agents
are based on condition-action rules, implemented with an
appropriate production system. They are stateless devices
which do not have memory of past world states.
3. Agents with memory
have internal state, which is used to keep track of past states of
the world.
4. Agents with goals
are agents that, in addition to state information, have goal
information that describes desirable situations. Agents of this
kind take future events into consideration.
5. Utility-based agents
base their decisions on classic axiomatic utility theory in
order to act rationally.

Table Driven Agents
 Table lookup of percept-action pairs mapping
from every possible perceived state to the optimal
action for that state
 Problems
◦ Too big to generate and to store (Chess has about
10120 states)
◦ No knowledge of non-perceptual parts of the current
state
◦ Not adaptive to changes in the environment; requires
entire table to be updated if changes occur
◦ Looping: Can’t make actions conditional on previous
actions/states.

Simple Reflex Agent
 An agent whose action depends only on the current
percepts.
 Rule-based reasoning to map from percepts to
optimal action; each rule handles a collection of
perceived states
 Problems
◦ Still usually too big to generate and to store
◦ Still no knowledge of non-perceptual parts of state
◦ Still not adaptive to changes in the environment; requires
collection of rules to be updated if changes occur
◦ Still can’t make actions conditional on previous state

Table Driven/Reflex Agent Architecture

Agents with Memory
 Encode “internal state” of the world to remember
the past as contained in earlier percepts.
 Needed because sensors do not usually give the
entire state of the world at each input, so
perception of the environment is captured over
time. “State” is used to encode different "world
states" that generate the same immediate percept.
 Requires ability to represent change in the world;
one possibility is to represent just the latest state,
but then can’t reason about hypothetical courses
of action.

Architecture for an Agent with Memory

Goal Based Agents
 Choose actions so as to achieve a (given or
computed) goal.
 A goal is a description of a desirable situation.
 Keeping track of the current state is often not
enough  need to add goals to decide which
situations are good
 Deliberative instead of reactive.
 May have to consider long sequences of possible
actions before deciding if goal is achieved –
involves consideration of the future, “what will
happen if I do...?”

Architecture of Goal Based Agent

Utility based Agents
When there are multiple possible alternatives,
how to decide which one is best?
 A goal specifies a crude distinction between a happy and
unhappy state, but often need a more general
performance measure that describes “degree of
happiness.”
 Utility function U: State  Real indicating a measure of
success or happiness when at a given state.
 Allows decisions comparing choice between conflicting
goals, and choice between likelihood of success and
importance of goal (if achievement is uncertain).

Architecture for Utility based Agent

Summary
 An Agent perceives and acts in an environment, has an
architecture, and is implemented by an agent program.
 An Ideal agent always chooses the action which
maximizes its expected performance, given its percept
sequence so far.
 An Autonomous agent uses its own experience rather
than built-in knowledge of the environment by the
designer.
 An Agent program maps from percept to action and
updates its internal state.
 Reflex agents respond immediately to percepts.
 Goal-based agents act in order to achieve their
goal(s).
 Utility-based agents maximize their own utility
function.
 Representing knowledge is important for successful

Artificial Intelligence

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