Computer simulations have become a valuable tool for the mathematical modeling of many natural systems in physics (computational physics), astrophysics, climatology, chemistry, biology and manufacturing, human systems in economics, psychology, social science, health care and engineering. For example, computer simulations are now used to study how stars form and evolve; how climate change affects Earth’s environment; how cellsmultiply and interact to create tissues and organs; how materials fracture under various conditions; how aircraft fly; and how new pharmaceuticals are developed.