Machine Learning Methods for Ranking in Information Retrieval: When LambdaRank Gradient Incoherency Leads to Unfair Training

This study was funded by the European Union - NextGenerationEU, in the framework of the iNEST - Interconnected Nord-Est Innovation Ecosystem (PNRR M4C2I1.5, iNEST ECS00000043 – CUP H43C22000540006). The views and opinions expressed are solely those of the authors and do not necessarily reflect those of the European Union, nor can the European Union be held responsible for them. The report was developed as part of the activities carried out by Spoke 6, Research Topic 1 (New Digital Technologies), Task S1_3.4 (Novel methodologies for optimal recommendation by empowering Machine Learning algorithms and Learning-to-Rank models).