where Y stands for national product, K and L for the inputs of capital stock and labor, respectively, all in year t; a and 1 a are the output elasticities of the two inputs. At is a technology index which measures the cumulated effect of technological change (shifts in the production function) over time. Its position implies that technical change is assumed Hicksneutral in character. Neoclassical growth models also usually assume that labor and technology grow exponentially at the rates n and g, respectively: