Development of recommender system algorithms for cold-start problem

Cold-start problems are one of the most important challenges in recommendation systems. In this thesis, we proposed models to develop solutions for the cold-start problem from two different perspectives. We aimed for a deterministic and a heuristic study that can be used in different scenarios. In the first perspective, we introduced a new heuristic framework that optimizes item-based similarity models to provide top-N recommendation lists using Continuous Ant Colony Optimization with a non-deterministic approach. Thanks to its heuristic structure, we aimed to create specific recommendation lists for users and change them according to each session, while at the same time aiming to balance the relevance of the user and the item variety in the recommendation lists. In the second perspective, we introduced two new Collaborative Filtering techniques deterministically. In the first model, we developed an asymmetric similarity matrix among the items based on the z-score normalization of the Gram-matrix we obtained using the implicit data, and in the second model, we aimed to reduce the sparsity with the item predictions with the assist our novel item similarity matrix, thus enabling more accurate decomposition of the latent factors in the user-item matrix we provided. We evaluated all of our methods on well-known datasets and observed that our methods outperform similar recommendation models in a variety of scenarios, including cold-start users, cold-start systems, and providing of unpopular product recommendations.