The document discusses primal-dual algorithms as an approximation technique for optimization problems. It provides an overview and introduction to primal-dual algorithms. As an example, it describes how the minimum weighted vertex cover problem can be solved using a primal-dual strategy. Specifically, it formulates the problem as an integer linear program and linear program. Rather than fully solving the linear program, the primal-dual algorithm maintains feasible integer and dual solutions and iteratively derives more feasible solutions until the integer solution is feasible.