An approximation algorithm is a type of algorithm used in l'informatique and la recherche opérationnelle to find solutions to optimization problems where finding the exact solution is computationally infeasible. These algorithms aim to produce solutions that are close to the best possible answer, particularly in cases where the problem is NP-hard, meaning that no known polynomial-time algorithm can solve it optimally.
Approximation algorithms typically offer a performance guarantee, which is a ratio of the quality of the solution they produce to the quality of the solution optimale. This ratio is often referred to as the ratio d'approximation. For example, an algorithm with an approximation ratio of 2 guarantees that the solution will be at most twice as bad as the optimal solution.
Common types of problems tackled by approximation algorithms include the Traveling Salesman Problem, Knapsack Problem, and various graph-related problems. Different approaches are utilized based on the specific problem, such as greedy methods, programmation linéaire relaxation, et algorithmes aléatoires.
While approximation algorithms do not guarantee an exact solution, they are essential for solving large-scale instances of complex problems effectively and efficiently, making them a crucial tool in fields like intelligence artificielle, network design, and logistics.