What is A* Algorithm? What Are Its Basic Concepts?

A* Algorithm

AI is primarily motivated by the desire to solve issues of enormous computational complexity. These problems are now reduced to simple problems of search in the course of the span of time.


In a search problem it is the aim to determine a route from one location to another. There are a variety of methods to transform search issues into graphs. In our instance we’ll make use of edges to depict all the possible states along with edges that represent the entirety potential routes.

In this way the next obvious concern is:

What is an A* Algorithm?

Let’s say you need to navigate through an immense maze. The maze is so vast that traversing it on foot will take a significant amount of time. Also, you’ll be required to finish another maze following the previous maze “by foot. ”

This means that we can reduce the maze down to a simple search and create an approach that can be applied in any maze that we encounter, so long as it is based on the same structure and rules.

To convert any problem into a search issue it is necessary to determine the following six words:

A listing of all outcomes that could be possible
A listing of all outcomes that could be possible
Inquiring whether we’ve crossed the final line

A collection of actions that could be performed (in this instance, various direction of motion)

The traversal feature (a function that tells us where we’ll land when we travel in a specific direction)
Costs associated with shifting from one state to another (which correspond to edges on the graph)
If we can convert junctions into points (red dots) and potential routes to graph edges that are suitable We can then solve the maze issue (blue line).

Naturally we will define the start and ending states as the intersections that we cross when we are entering into the maze (node A) and want to get out of this maze (node B).

In the final phase, we will talk about the best route from one place in the graph to the next. BFS, DFS, and Dijkstra are all sufficient in the most basic of situations (such like this) in which the graph is restricted in the number of edges and nodes.

Real-world problems have a greater complexity of combinatorial computation, thus dealing with an abundance of edges and nodes is a given. As an example the nature of the Rubik’s cube can be in various states is what makes the puzzle complicated to resolve. Therefore it is necessary to use an algorithm that is guided. In this scenario,* the intelligent algorithm for searching comes to light.

The phrase “informed search”

simply means that the algorithm is able to access additional information right from the beginning. For example, take the situation of a algorithm that is not able to access prior understanding of the surrounding.

But, a well-informed search problem algorithm might involve finding the most efficient route to take from your home to work using your eyes (seeing the route that will bring the closest to your destination) or a map for instance (knowing precisely how far each point is from the destination).

Contrary to other graph-traversal algorithms A* takes only one step when it is plausible and sensible in light of its function. It is always moving towards the desired goal, and does not consider any unoptimal actions.

Artificially intelligent systems can greatly benefit from the use of A*, specifically when it comes to machines Learning and game design, since these systems simulate real-world situations.

The graph-traversal techniques Their uses and their differences are detailed on this page.

A* Algorithm Concept

A* is a variant of the best-first algorithm that is built on algorithms that use heuristics to achieve the highest level of accuracy and totality.

When a search engine has the attribute of optimality it is guaranteed to determine the most effective solution, in this case the shortest path to the final state. If a search engine has the attribute of completeness it means it will definitely find solutions to any given problem.

Every time the A* moves into a state it calculates the cost to travel f(n) (n is the next node), and then is able to enter the node by using most value f(n).

The formula below is used to calculate these numbers:

the lowest value of f(n)

g(n) determines the most efficient route between the beginning and the end nodes. h(n) can be described as an approximate heuristic estimation of the worth for the particular node.

In order to rebuild any path one must connect each node with the relative having the highest f(n) amount. This implies that whenever we look at particular nodes, we should also update their best relations.

The efficiency of the algorithm A* is mostly dependent on the heuristic number h(n) and, based on the nature of the problem an alternative heuristic algorithm could be needed to find the most efficient solution.

The development of such capabilities isn’t an easy task, and is among the most fundamental challenges in artificial intelligence. Acceptability and consistency are two most fundamental attributes an heuristic task could have.

Admissibility and Consistency

A heuristic equation h(n) is acceptable as long as it does not exceed the real distance between the node in question and n.

Therefore this formula is the same for every node:

A heuristic function h(n)

Distance between the n node and destination node is indicated as h*(n). If, however, it overestimates the real distance, but never any more than the value of d then we can confidently conclude that the result produced through the program is true to the value of d (i.e. it doesn’t exaggerate the shortest distance between B and A by more than).

A Heuristic formula h(n) is consistent in the event that the distance between the desired n and the neighbor is always less and equal to estimated cost of achieving the neighbour

heuristic function h(n)

The distance between two nodes is indicated with c(n,m). In addition when h(n) stays constant then we know the best route to each node that was examined prior to. This suggests that the function is performing optimally.


This is a way to implement A* on a graph structure in all its aspects. To keep things simple and clear the heuristic formula is stated as 1. for all nodes.

The graph is represented by an adjacency list. Where the keys correspond to graph’s nodes and the values are an array of edges connecting the nodes.

This section describes the Python application of the A* algorithm.:

Python implementation of the A* algorithm

Python implementation of the A* algorithm


We implement this code according to the following:

the code

The output could be:


In the end the best route to take between A through D measured by A* A->B->D.


A* can be described as an extremely powerful algorithm with a virtually limitless possibilities. However, it is only as effective as its heuristics function. That can vary greatly based on the specifics of the problem.

It has been used in a myriad of software systems. That range from machine learning optimizing search to game development. Require non-player characters to navigate through a maze of obstacles and terrain to get to the player.

You may also like:


Please enter your comment!
Please enter your name here