Who pointed out that the businessman always studies his production function and his input prices and substitutes one input for another till his costs become the minimum possible?

Operations research, often shortened to the initialism OR, is a discipline that deals with the development and application of analytical methods to improve decision-making. The term management science is occasionally used as a synonym. (Source: Wikipedia)

Examples of operation research models are: a map, activity charts balance sheets, PERT network, break-even equation, economic ordering quantity equation etc.