MullOverThing

Useful tips for everyday

# What is Q function in MDP?

## What is Q function in MDP?

A Q-value function (Q) shows us how good a certain action is, given a state, for an agent following a policy. The optimal Q-value function (Q*) gives us maximum return achievable from a given state-action pair by any policy.

## What is the V function?

The V-function: the value of the state. More formally, the V-function, also referred to as the state-value function, or even the value function, or simply V, measures the goodness of each state. In other words, how good or bad it is to be in a particular state according to the return G when following a policy 𝜋.

What are Q values in MDP?

There are two important characteristic utilities of a MDP — values of a state, and q-values of a chance node. The * in any MDP or RL value denotes an optimal quantity. Q-value of a state, action pair: The q-value is the optimal sum of discounted rewards associated with a state-action pair.

Can Q value infinity?

Q(K, A) only grows to approach that; not infinitely. When it stops growing (has approximated its actual value), the Q(K, A) for other A s can catch up.

### Which is better the Q function or the V function?

From a sampling perspective, the dimensionality of Q ( s, a) is higher than V ( s) so it might get harder to get enough ( s, a) samples in comparison with ( s). If you have access to the transition function sometimes V is good. There are also other uses where both are combined.

### Which is the correct definition of the V / Q ratio?

The V/Q ratio can therefore be defined as the ratio of the amount of air reaching the alveoli per minute to the amount of blood reaching the alveoli per minute—a ratio of volumetric flow rates.

How is the V / Q ratio of the lungs measured?

V/Q ratio is measured using a test called a pulmonary ventilation/perfusion scan. It involves a series of two scans: one to measure how well air flows through your lungs and the other to show where blood is flowing in your lungs.

What is the Q function in Bellman equation?

In post 2 we extended the definition of state-value function to state-action pairs, defining a value for each state-action pair, which is called the action-value function, also known as Q-function or simply Q.