MullOverThing

Useful tips for everyday

# Can you prune Expectiminimax?

## Can you prune Expectiminimax?

Expectimax requires the full search tree to be explored. There is no type of pruning that can be done, as the value of a single unexplored utility can change the expectimax value drastically. Therefore it can be slow.

## How do you apply alpha-beta pruning?

Following are some rules to find good ordering in alpha-beta pruning:

1. Occur the best move from the shallowest node.
2. Order the nodes in the tree such that the best nodes are checked first.
3. Use domain knowledge while finding the best move.
4. We can bookkeep the states, as there is a possibility that states may repeat.

How does alpha-beta pruning technique work?

Alpha–beta pruning is a search algorithm that seeks to decrease the number of nodes that are evaluated by the minimax algorithm in its search tree. It is an adversarial search algorithm used commonly for machine playing of two-player games (Tic-tac-toe, Chess, Go, etc.).

### Does the alpha-beta pruning can be applied?

Explanation: Alpha–beta pruning can be applied to trees of any depth and it is possible to prune entire subtree rather than leaves. Explanation: Alpha and beta are the values of the best choice we have found so far at any choice point along the path for MAX and MIN.

### Is pruning possible in an Expectimax tree?

(d) If leaf values are constrained to be nonnegative, is pruning ever possible in an expectimax tree? Give an example, or explain why not. Solution: No pruning is possible.

Is Expectimax better than Minimax?

As evident from the results, Expectimax is quite dominant over minimax (similar results can be seen without alpha-beta pruning in minimax) in terms of results produced. Both use the same evaluation function and do not proceed any further than 3 moves.

#### Why is it called alpha-beta pruning?

It is called Alpha-Beta pruning because it passes 2 extra parameters in the minimax function, namely alpha and beta. Let’s define the parameters alpha and beta. Alpha is the best value that the maximizer currently can guarantee at that level or above.

#### Can all MDPs be solved using Expectimax search?

(a) True/False: All MDPs can be solved using expectimax search. False. MDPs with self loops lead to infinite expectimax trees. Unlike search problems, this issue cannot be addressed with a graph-search variant.

What is Negamax algorithm?

Negamax search is a variant form of minimax search that relies on the zero-sum property of a two-player game. This algorithm relies on the fact that. to simplify the implementation of the minimax algorithm. More precisely, the value of a position to player A in such a game is the negation of the value to player B.

## How does alpha beta pruning improve minimax algorithm?

Alpha-Beta pruning is not actually a new algorithm, rather an optimization technique for minimax algorithm. It reduces the computation time by a huge factor. This allows us to search much faster and even go into deeper levels in the game tree.

## When does the minimax algorithm break at C?

At C, beta = min ( +INF, 2). The condition beta <= alpha becomes true as beta = 2 and alpha = 5. So it breaks and it does not even have to compute the entire sub-tree of G. The intuition behind this break off is that, at C the minimizer was guaranteed a value of 2 or lesser.

Which is the best alpha or beta for Min?

Alpha: It is the best choice so far for the player MAX. We want to get the highest possible value here. Beta: It is the best choice so far for MIN, and it has to be the lowest possible value. Note: Each node has to keep track of its alpha and beta values.

### How to calculate Alpha and beta in game theory?

At F, alpha = 5 and beta = +INF. F looks at its left child which is a 1. alpha = max ( 5, 1) which is still 5. F looks at its right child which is a 2.