Graphs in theory

Graph theory has a humble beginning, as a solution to a puzzle. Residents of the Prussian city of Kongisberg, which was bisected by a river, had long pondered this puzzle. It took Leonard Euler, a mathematician, to not only solve the problem but to do so in such a novel way that his solution launched a new field of mathematics. This chapter reviews the early history of graph theory, starting with the famous story of the seven bridges of Konigsberg. It will also present other early and historically significant uses of graph theory such as Stanley Milgram’s landmark “small world problem” study. Some fundamental topics are introduced such as vertexes and edges. We close out the chapter with an exploration of the four color problem, which was explored and solved using a special type of graph called a planar graph. The four color theorem inspired a mathematician who today lends his name to a graph-inspired distance metric tracked by mathematicians, the Erdos number.