If a traveling salesman has to visit a set number of cities in a set number of days what is the shortest route he can take to cover all his stops and then return home?  And does the answer to this question relate in any way to the manner in which a shopper navigates her way through a grocery store? In a new paper Wharton marketing professors Peter S. Fader and Eric T. Bradlow and doctoral student Sam K. Hui use a concept known as the ”Traveling Salesman Problem” to study the efficiencies -- and inefficiencies -- of grocery shoppers.