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ANT COLONY OPTIMIZATION ALGORITHM STEP-BY-STEP WITH EXAMPLE

 Ant colony optimization algorithms


Do you know: How the Ant Colony Optimization algorithm works?  

We all know about ants. Researchers have estimated about 13800 known ant species. In an ant colony, there is Queen (i.e., female ant), fertilized male ant (also known as drone), female ant workers, and soldiers. Queen ant can live up to 30 years. Ants live in colonies (also known as ant nest). An average ant colony contains 1000 individual ants and an ant super colony can contain 300 million individual ants. Ants communicate with each other indirectly using pheromones, sound, and touch.

Ant colony optimization is a Nature Inspired Population Based Metaheuristic Optimization Algorithm. Ant colony optimization (ACO) is inspired by the real ant food searching behavior. Ant colony optimization algorithm is basically inspired by the pheromone-based ant communication. Ant colony optimization is developed by Marco Dorigo in 1992.  Author developed this algorithm to solve Discrete Variable Combinatorial Optimization Problems. Today it is also applied to solve Continuous Variable and other problems as well. ACO is a Stochastic technique used for solving Computational Problems [such as Finding Optimal Path / Finding Shortest Path through Graph].

Ant colony optimization technique is used to find Optimal paths, Routing, and load balancing problems. Best known example: Travelling Salesman Problem (TSP). ACO Terminology: Pheromones, Pheromones Trials, Pheromone Density, and Pheromone Evaporation.

Q. How Ant’s Communicate with each other? 

A. Ant’s can easily communicate with each other using Pheromones.

Q. How do other ants follow pheromones? 

A. Ants leave pheromones on the soil. That can be easily followed by other ants.

Q. How do ants find out the shortest path between Nest and Food?

A. Ants communicate with each other indirectly using pheromones. With the help of Pheromone signals, ants can easily find the shortest path between Nest/Colony and Food.

Ant Colony Optimization (ACO) Algorithm Step-by-Step
Step 1. Initialize ACO parameters
Step 2. Ant Solution Construction
Step 3. Position Each ant in the stating node. 
Step 4. Each ant will select the next node by applying the state transition rule.
Step 5. Repeat until ant builds the best solution, then Compute the fitness value.
Step 6. Update the best solution.
Step 7. Apply offline pheromone update. 
Step 8. Display the best result.
Step 9. Stop

For more details, you can visit this video (Ant colony optimization) given below. 
Ant Colony Optimization Algorithm step-by-step with Example (ACO) ~xRay Pixy 🌿🍰🐜🐜🐜🌞

Topics Covered in this video:
Introduction to ant colony optimization algorithm
Ant Life Cycle
Ant Communication
Ant Colony Optimization Algorithm
Real Ant foraging behavior
Artificial Ant foraging behavior
Ant Colony Optimization algorithm step-by-step with Example
ACO Limitation and Advantage 

PART 02: How Ant Colony Optimization is applied to solve Traveling Salesman Problem?

Traveling Salesman Problem: In traveling salesman problem, salesman want to visit a number of cities and cover minimum distance during tour.

Constraint: Each city should be visited exactly once. [to minimize tour length]

Ant Colony Optimization is applied on Traveling Salesman Problem to solve this problem. A number of Artificial Ants are used. We will use Artificial ants to visit all cities and calculate tour length for each ant. Out of (n) ants, check feasible solution i.e., feasible tour with minimum tour length.

Ant Goal: Find out Feasible Tour for the salesman problem.

Objective function Value: Sum of distance between each city visited during tour.

Ant Colony Optimization Metaheuristics for TSP Steps

Step 01: Construct Graph for the given problem. Each city is considered as graph NODES / VERTICES and distance between cities are graph EDGES.

Step 02: Initialize all important parameters, Number of Artificial Ants, Maximum Iterations, Artificial Pheromones and other.

Step 03: For any Ant select ant city randomly. Place that ant in randomly Selected city.

Step 04: Build the Tour for Ant from randomly selected city to unvisited cities. Ants are also using artificial memory to store visited city.

Step 05: One by one move ant to all the unvisited cities and calculate tour length.

Step 06: Once no unvisited city left. Ant will return to the randomly selected city. Then calculate Total Tour Length. Repeat this for all ants.

Step 07: Update Artificial Pheromones Values. 

Step 08: Check stopping criteria. If stopping criteria is not matched repeat loop ELSE display the best solution.

For More Details and Numerical Example you can visit this video.

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#aco
#Metaheuristic #Algorithms
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