Submodular set function

Submodular set functions are like a 'scorecard' for how useful or valuable different groups of things are. This 'scorecard' can be used to determine the best combination of things to use, so that the most valuable result is achieved. Think of it like going to a store and trying to figure out what combination of items to buy, so that you get the best value without spending too much money. Submodular set functions provide a way to mathematically measure the value of different combinations, so that a 'perfect' combination can be found.