In this section, we describe our new approach to the NAM
based on column generation. We begin by creating an equivalent formulation of the NAM from a
subset of the original constraints which serves as the master problem. Each column in the master
problem represents a feasible assignment of nurses to a particular case over the planning
horizon; that is, the specification of the yickh variables for case c . We start with a small
set of columns and generate more as needed. This is done by solving one subproblem
for each surgery case at each iteration of the algorithm.