Problem: I have $i$ jobs that I can assign to $j$ workers. Each job has a cost. Each worker can perform up to an arbitrary max number of jobs. However, there is a cost efficiency for each job that is assigned to the worker. For example, if two jobs are assigned then the cost of the jobs is multiplied by $0.95$. Three jobs, by $0.90$. This function can also be linear.
Are there any examples of this in literature? I've been able to implement this if the multiplicative cost function is a step function. I'm not exactly sure how to proceed if the value that I multiply against the number of jobs is a function.