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# Markov decision process (MDP)

### the tl;dr

A Markov decision process (MDP) is a mathematical framework for modeling decision-making in situations where outcomes are partly random and partly under the control of a decision-maker.

## What is a Markov decision process?

A Markov decision process, or MDP, is a mathematical framework for modeling decision-making in situations where outcomes are uncertain. MDPs are commonly used in artificial intelligence (AI) to help agents make decisions in complex, uncertain environments.

MDPs are based on the concept of a Markov chain, which is a mathematical model of a system where the future state of the system is determined by its current state. In an MDP, the current state of the system is called the "state" and the possible future states are called "states." The agent makes a decision at each state, which determines the next state of the system. The agent's goal is to find a policy, which is a set of decisions, that will maximize some goal or reward.

MDPs are powerful tools for modeling decision-making, but they are also complex and can be difficult to solve. In many cases, it is not possible to find an optimal policy for an MDP. However, there are a variety of methods that can be used to approximate an optimal policy. These methods include value iteration, policy iteration, and Q-learning.

## What is the Bellman equation?

The Bellman equation is a fundamental equation in AI that is used to define the optimal value function for a given Markov decision process. The equation is named after Richard Bellman, who first proposed it in the 1950s. The equation is used to find the optimal policy for a given MDP by solving for the value function that satisfies the Bellman equation. The Bellman equation is also known as the dynamic programming equation.

## What is dynamic programming?

Dynamic programming is a technique for solving problems by breaking them down into smaller subproblems. It is typically used for optimization problems, where the goal is to find the best solution.

Dynamic programming is a powerful technique that can be used to solve many different types of problems. In AI, it is often used to find the best solution to a problem, such as the shortest path from one point to another.

## What is value iteration?

Value iteration is a technique used in artificial intelligence (AI) for finding the optimal value of a function. It is a form of dynamic programming that iteratively updates the value of a function by taking into account the values of its neighboring functions. The technique is used to find the best path through a graph or network.

## What is policy iteration?

Policy iteration is an AI technique used to find an optimal policy for a Markov decision process (MDP). It works by alternately solving for the value function of the MDP and then finding the policy that is optimal with respect to that value function.

This technique can be used to find an optimal policy for any MDP, even those with very large or infinite state spaces. However, it can be computationally expensive, so it is often used only when other methods have failed.