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5 - Planning and Decision Making

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Introduction to Planning in AI

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Teacher
Teacher

So class, today we dive into planning, which is a critical component of AI. Can anyone tell me why planning is essential for AI agents?

Student 1
Student 1

I think it's because they need to make decisions rather than just react.

Teacher
Teacher

Exactly! Planning allows AI to operate in complex, dynamic environments and pursue long-term goals. It’s more than just reacting; it’s about strategically deciding what to do next.

Student 2
Student 2

Can you give an example of where this planning is used?

Teacher
Teacher

Sure! Planning is crucial in robotics, logistics, and even gaming AI. Picture a robot navigating a maze; it must plan its path to the exit rather than just bumping into walls.

Student 3
Student 3

What components are needed for making a plan?

Teacher
Teacher

Great question! Every planning system consists of an initial state, a goal state, possible actions, and the actual plan—a sequence of actions leading to the goal. Remember the acronym I-P-G-A: Initial state, Plan, Goal state, Actions.

Student 4
Student 4

What do we have to consider when planning?

Teacher
Teacher

You must consider action preconditions and the effects of those actions on the environment, plus the entire search space of plans. It’s about making well-informed choices that lead to success.

Teacher
Teacher

In summary, planning is about thoughtful actions that lead to achieving goals in complex settings. Planning agents analyze possible actions before moving, setting them apart from reflex agents.

STRIPS and Goal Stack Planning

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Teacher
Teacher

Now that we've established what planning is, let’s look at a useful planning tool called STRIPS.

Student 1
Student 1

What is STRIPS exactly?

Teacher
Teacher

STRIPS is a formal language that helps break down planning actions into manageable parts. These parts include preconditions, an add list, and a delete list. For instance, moving from one location to another.

Student 2
Student 2

Can you give an example of those lists?

Teacher
Teacher

Sure! Consider the action 'Move(x, y)'. The precondition might be that you are at x and that x is connected to y. After the move, the status 'At(y)' will become true while 'At(x)' will become false.

Student 3
Student 3

That seems helpful! What's Goal Stack Planning?

Teacher
Teacher

Goal Stack Planning is a backward-chaining method where we start with the desired goal and work backward, checking conditions and actions until everything is satisfied.

Student 4
Student 4

What are the advantages of this approach?

Teacher
Teacher

It’s particularly effective for complex tasks, allowing for the reuse of actions and subgoals. But remember, it struggles in uncertain environments—so it assumes a deterministic world.

Teacher
Teacher

To wrap up this session, STRIPS simplifies planning in AI through logical manipulation, while Goal Stack Planning helps achieve complex goals systematically.

Markov Decision Processes (MDPs)

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Teacher
Teacher

Lastly, we’ll explore Markov Decision Processes, or MDPs, which provide a framework for making decisions when outcomes are uncertain. Why might we need this?

Student 1
Student 1

Maybe because not everything can be predicted?

Teacher
Teacher

Exactly! In the real world, actions can lead to unpredictable results, and MDPs help manage this with a structured approach.

Student 2
Student 2

What makes up an MDP?

Teacher
Teacher

An MDP includes a set of states, actions, a transition function that defines probabilities, a reward function, and the discount factor, which indicates the preference for immediate over future rewards.

Student 3
Student 3

So how do we find the best action if everything is uncertain?

Teacher
Teacher

Great question! We establish a policy, which maps states to actions, in order to maximize expected rewards over time. This is done usually via value iteration or policy iteration.

Student 4
Student 4

What are some applications of MDPs?

Teacher
Teacher

MDPs are used in various fields, like robotics for path planning under uncertainty, inventory control, game-playing AI, and healthcare decision systems.

Teacher
Teacher

In summary, understanding MDPs enables AI to navigate the complexities of uncertain environments effectively.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section explores the fundamentals of planning and decision-making in AI, detailing the essential components, mechanisms like STRIPS, Goal Stack Planning, and Markov Decision Processes (MDPs).

Standard

In this section, we delve into the importance of planning in AI, emphasizing its role in complex environments and long-term goal achievement. Key frameworks such as STRIPS, Goal Stack Planning, and Markov Decision Processes are examined, highlighting their components, applications, and the challenges faced in non-deterministic scenarios.

Detailed

Planning and Decision Making in AI

Introduction to Planning in AI

Planning is a fundamental aspect of Artificial Intelligence that involves formulating a series of actions to transition an agent from an initial state to a target goal state. Unlike simple reflex mechanisms, planning agents rationalize their next actions in a structured manner.

Why is Planning Needed?

  • It allows AI to operate in intricate, ever-changing conditions.
  • It aids in achieving long-term objectives.
  • It is crucial across various domains, including robotics, logistics, and gaming.

Components of a Planning System

  1. Initial State: Defined starting point of the agent.
  2. Goal State: The desired outcome of the plan.
  3. Actions (Operators): Transformative steps applicable to the world.
  4. Plan: Series of actions leading to the goal.
    Planning systems must also address:
  5. Action Preconditions: Conditions required for actions to take place.
  6. Effects of Actions: The resulting changes in the underlying environment.
  7. Search Space: The encompassing landscape of possible plans.

STRIPS and Goal Stack Planning

STRIPS Overview

STRIPS (Stanford Research Institute Problem Solver) is a framework for representing planning issues through logical action breakdowns, encapsulating:
- Preconditions: Conditions that must be fulfilled prior to the action.
- Add list: Effects that become true post-action.
- Delete list: Effects that no longer hold true.
For example, the action Move(x, y) involves:
- Preconditions: At(x) ∧ Connected(x, y)
- Add: At(y)
- Delete: At(x)
STRIPS transforms planning into a manageable form of logical statement manipulations for better reasoning.

Goal Stack Planning

This method utilizes a backward-chaining approach where goals are placed in a stack, and actions are executed to satisfy these goals step-by-step.
- Advantages: Manages complex, multi-step tasks and optimizes the reuse of actions.
- Limitations: Faces difficulties in non-deterministic situations and assumes a fully observable world.

Markov Decision Processes (MDPs)

MDPs offer a mathematical structuring for decision-making under uncertainty.

MDP Components

  1. S: Set of possible states.
  2. A: Set of actions.
  3. T(s, a, s′): Transition function defining probabilities of reaching state s′ post action a in state s.
  4. R(s, a, s′): Reward function giving immediate rewards after transitioning.
  5. γ (gamma): Discount factor indicating the value of future rewards.

MDP Goals

The aim is to discover a policy π(s) that maps states to actions, maximizing expected utility over time.

Solving MDPs

Two main strategies include:
- Value Iteration: Updates each state's value based on future rewards, utilizing Bellman’s equation.
- Policy Iteration: Continuously fine-tunes the policy based on the valuation of states.

MDP Applications

  • Robotics (navigating with unpredictable variation),
  • Inventory management,
  • Game AI,
  • Healthcare decision processes.
    In conclusion, planning and decision-making frameworks empower AI systems to transcend mere reactive behavior, addressing challenges in both predictable and unpredictable settings.

Audio Book

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Introduction to Planning in AI

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Planning is a key area of Artificial Intelligence that focuses on generating a sequence of actions that leads an agent from an initial state to a desired goal state. Unlike simple reflex agents, planning agents deliberate about "what to do next" in a structured and efficient way.

Detailed Explanation

Planning in AI involves creating a series of actions that help an agent move from where it currently is to where it wants to be. This is different from basic reflex agents that act based only on the current situation without thinking ahead. Planning agents are capable of strategizing their actions in a methodical way to reach their objectives efficiently.

Examples & Analogies

Think of a GPS navigation system. It doesn't just tell you where to go next; it also considers your starting location, your destination, and other routes to provide you with the best path. Similarly, planning agents assess various options before deciding the best action to reach their goals.

Why Planning?

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• Operates in complex, dynamic environments.
• Supports long-term goal achievement.
• Essential for robotics, logistics, game AI, and more.

Detailed Explanation

Planning is crucial because it allows agents to function effectively in environments that may change and are complicated. Without planning, achieving longer-term goals would be difficult as agents could only react to immediate situations. Planning enhances capabilities in various fields, such as robotics, where robots must navigate and operate in unpredictable settings, or in logistics for efficient distribution of goods.

Examples & Analogies

Imagine organizing a surprise birthday party. You can't just react to events; you need to plan steps like booking a venue, inviting guests, and coordinating food. Just as party planning requires foresight and preparation, AI systems need structured planning to succeed in complex scenarios.

Components of a Planning System

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• Initial State: The known starting point.
• Goal State: The desired outcome.
• Actions (Operators): Changes that can be made to the world.
• Plan: A sequence of actions that leads to the goal.

Planning agents must consider:
• Action preconditions (when actions are possible).
• Effects of actions (how the world changes).
• The overall search space of plans.

Detailed Explanation

A planning system consists of several key components. The initial state is where the agent begins, while the goal state defines where it wants to go. Actions or operators represent changes the agent can make, leading up to the creation of a plan, which is a sequence of actions to reach the goal. Additionally, agents need to account for when actions can occur and what the consequences of those actions will be, while navigating through the possible combinations of actions.

Examples & Analogies

If you're baking a cake, the initial state is your empty kitchen, and your goal state is a finished cake. Your actions include mixing ingredients and baking. You must plan what tools you need, which ingredients you have, and the order of tasks (your plan) to successfully create the cake. Each step has preconditions (like having the oven ready) and effects (like assembling the cake once baked).

STRIPS and Goal Stack Planning

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5.2 STRIPS and Goal Stack Planning
5.2.1 STRIPS (Stanford Research Institute Problem Solver)
STRIPS is a formal language used to represent planning problems. It breaks down actions into:
• Preconditions: What must be true before the action.
• Add list: Facts made true by the action.
• Delete list: Facts made false by the action.
Example: Move(x, y)
• Preconditions: At(x) ∧ Connected(x, y)
• Add: At(y)
• Delete: At(x)
STRIPS simplifies planning into symbolic manipulation of logical statements, making it easier to reason about actions and outcomes.

Detailed Explanation

STRIPS stands for Stanford Research Institute Problem Solver and is a formal way to describe planning tasks. It organizes actions into three categories: Preconditions, which must be met for an action to occur; the Add list, which tracks new facts that come into play once an action is completed; and the Delete list, which notes any facts that are negated by the action. This structured format helps simplify complex planning tasks by breaking them down into logical components.

Examples & Analogies

Consider someone trying to find their way around a new city. The precondition might be knowing where they currently are and if a route exists. The 'add' might be finding a location they can walk to, while the 'delete' might involve noting that they are no longer in their original location. STRIPS helps map out their journey logically.

Goal Stack Planning

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5.2.2 Goal Stack Planning
Goal Stack Planning is a top-down, backward-chaining approach that starts from the goal and works backward to the initial state.
Process:
1. Place the goal on a stack.
2. Pop the goal and determine if it's satisfied.
3. If not, find an action that achieves it and push its preconditions.
4. Repeat until all conditions are satisfied.
Advantages:
• Handles complex, multi-step problems.
• Reuses actions and subgoals.
Limitations:
• Struggles with nondeterministic or uncertain environments.
• Assumes a deterministic, fully observable world.

Detailed Explanation

Goal Stack Planning is a method where the planning begins from the goal and works backward to understand how to achieve it. It involves placing the goal on a stack, checking if it can be fulfilled, and if not, identifying the actions needed to reach that goal. While this approach effectively tackles complex challenges and allows for reusing actions and goals, it does have limits, particularly in unpredictable situations where outcomes may vary.

Examples & Analogies

Imagine you're assembling a Lego set. You start with the final model as your goal. You then work backward to determine which pieces you need, checking if you have them, and pulling out the individual steps to put them together. This backward approach is similar to Goal Stack Planning, which can be efficient but may not always account for unexpected missing pieces (like a piece not fitting).

Markov Decision Processes (MDPs)

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5.3 Markov Decision Processes (MDPs)
In real-world scenarios, outcomes of actions are often uncertain. Markov Decision Processes provide a mathematical framework for decision making under uncertainty.
5.3.1 MDP Definition
An MDP is defined by:
• S: Set of states
• A: Set of actions
• T(s, a, s′): Transition function – probability of reaching state s′ after taking action a in state s
• R(s, a, s′): Reward function – immediate reward received after transition
• γ (gamma): Discount factor – represents preference for immediate rewards over future rewards (0 ≤ γ ≤ 1)

Detailed Explanation

Markov Decision Processes (MDPs) are used when the result of actions is uncertain. An MDP is defined by a set of possible states (S) and actions (A) that can be taken in those states. The transition function (T) shows the probability of moving from one state to another after taking a specific action, while the reward function (R) indicates the immediate benefit received for making that transition. The discount factor (gamma) helps in determining how much importance is given to future rewards compared to immediate ones.

Examples & Analogies

Think of a decision while playing a board game where the outcome of each move can vary depending on the dice roll. You know the current state (your position on the board) and potential moves (actions). The transition function helps predict where you might land based on dice outcomes, and the rewards could be points or advantages, illustrating MDP concepts.

Objective and Solving of MDPs

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5.3.2 Objective of MDPs
The goal is to find a policy π(s): a mapping from states to actions that maximizes expected utility (or reward) over time.
5.3.3 Solving MDPs
Two primary methods:
• Value Iteration:
○ Iteratively updates values of each state based on expected future rewards.
Uses Bellman Equation:
V(s) = max_a ∑ [T(s, a, s′) × (R(s, a, s′) + γV(s′))]
• Policy Iteration:
○ Iteratively improves the policy by evaluating and improving the value function.

Detailed Explanation

The objective of MDPs is to find a policy, which is a strategy that defines the best action to take in every possible state to maximize the expected reward over time. There are two main techniques for solving MDPs: Value Iteration and Policy Iteration. Value Iteration calculates the value of each state based on possible future rewards using the Bellman Equation, while Policy Iteration improves the action choices over time to reach higher overall rewards.

Examples & Analogies

Returning to our board game analogy, a strategy can be seen as your game plan. Value Iteration would be like computing the best moves based on all possible future dice rolls and their outcomes, while Policy Iteration would involve adjusting your strategy as you learn more about the game as you play.

Applications of MDPs

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5.3.4 Applications of MDPs
• Robotics (path planning with uncertainty)
• Inventory control and resource allocation
• Game-playing AI
• Healthcare decision systems

Detailed Explanation

MDPs have a variety of applications in fields where uncertainty exists. In robotics, MDPs help robots understand the best paths to take when navigating unpredictable environments. In inventory control, they assist in making optimal decisions about stock replenishment and resource allocation to minimize costs. Game-playing AI uses MDPs to structure strategies where outcomes can vary based on player choices. In healthcare, MDPs can guide clinicians in making treatment decisions based on varying patient responses.

Examples & Analogies

Imagine a delivery drone navigating a busy city. It must adapt to changing weather, obstacles, and traffic conditions, paralleling how MDPs allow for strategic path planning under uncertainty. Similarly, in a board game you might encounter unpredictable challenges, and you must use the best strategy to win despite these uncertainties.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Planning: A critical component of AI focused on generating a sequence of actions.

  • STRIPS: A formal representation method for planning problems.

  • Goal Stack Planning: A backward chaining method for achieving goals.

  • Markov Decision Processes: A framework for decision-making under uncertainty.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • An AI robot navigating through a maze using planning to avoid obstacles and reach the exit.

  • Using STRIPS to define the actions necessary for a vehicle to reach a destination, including preconditions and outcomes.

  • Implementing MDPs in a game-playing AI where the agent must decide its next move based on possible outcomes.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • When planning an AI’s route, Make sure to list the actions out!

📖 Fascinating Stories

  • An AI robot embarks on a quest in a labyrinth, having to plan each step cautiously to avoid traps and find treasures – each choice contrary to another brings a new path and possibilities.

🧠 Other Memory Gems

  • To remember STRIPS: Precondition, Action Done (Add), Forget (Delete); P-A-F!

🎯 Super Acronyms

For planning components, use the acronym I-P-G-A

  • Initial state
  • Plan
  • Goal state
  • Actions.

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: Planning

    Definition:

    The process of generating a sequence of actions leading from an initial state to a desired goal state.

  • Term: Initial State

    Definition:

    The known starting point of the planning process.

  • Term: Goal State

    Definition:

    The desired final outcome the planning aims to achieve.

  • Term: Operators

    Definition:

    Actions or changes that can be made within the planning domain.

  • Term: STRIPS

    Definition:

    A formal language for representing planning problems by decomposing actions into preconditions and effects.

  • Term: Goal Stack Planning

    Definition:

    A backward-chaining approach to planning that starts with the goal and works backwards to achieve it.

  • Term: Markov Decision Process (MDP)

    Definition:

    A mathematical framework for making decisions in situations where outcomes are uncertain.

  • Term: State

    Definition:

    A specific condition or situation that an agent can be in within its environment.

  • Term: Action

    Definition:

    A decision or operation that can lead to a change in state.

  • Term: Policy

    Definition:

    A strategy that defines the best action to take in each state to maximize expected utility.