Concept
Fair item allocation is a kind of the fair division problem in which the items to divide are discrete rather than continuous. The items have to be divided among several partners who potentially value them differently, and each item has to be given as a whole to a single person. This situation arises in various real-life scenarios: Several heirs want to divide the inherited property, which contains e.g. a house, a car, a piano and several paintings. Several lecturers want to divide the courses given in their faculty. Each lecturer can teach one or more whole courses. White elephant gift exchange parties The indivisibility of the items implies that a fair division may not be possible. As an extreme example, if there is only a single item (e.g. a house), it must be given to a single partner, but this is not fair to the other partners. This is in contrast to the fair cake-cutting problem, where the dividend is divisible and a fair division always exists. In some cases, the indivisibility problem can be mitigated by introducing monetary payments or time-based rotation, or by discarding some of the items. But such solutions are not always available. An item assignment problem has several ingredients: The partners have to express their preferences for the different item-bundles. The group should decide on a fairness criterion. Based on the preferences and the fairness criterion, a fair assignment algorithm should be executed to calculate a fair division. These ingredients are explained in detail below. A naive way to determine the preferences is asking each partner to supply a numeric value for each possible bundle. For example, if the items to divide are a car and a bicycle, a partner may value the car as 800, the bicycle as 200, and the bundle {car, bicycle} as 900 (see Utility functions on indivisible goods for more examples). There are two problems with this approach: It may be difficult for a person to calculate exact numeric values to the bundles. The number of possible bundles can be huge: if there are items then there are possible bundles.