Investment (macroeconomics) in the context of "Depreciation"

Macroeconomics is a branch of economics that deals with the performance, structure, behavior, and decision-making of an economy as a whole. This includes regional, national, and global economies. Macroeconomists study topics such as output/GDP (gross domestic product) and national income, unemployment (including unemployment rates), price indices and inflation, consumption, saving, investment, energy, international trade, and international finance.

Macroeconomics and microeconomics are the two most general fields in economics. The focus of macroeconomics is often on a country (or larger entities like the whole world) and how its markets interact to produce large-scale phenomena that economists refer to as aggregate variables. In microeconomics, the focus of analysis is often a single market, such as whether changes in supply or demand are to blame for price increases in the oil and automotive sectors. From introductory classes in "principles of economics" through doctoral studies, the macro/micro divide is institutionalized in the field of economics. Most economists identify as either macro- or micro-economists.

A planned economy is a type of economic system where investment, production and the allocation of capital goods takes place according to economy-wide economic plans and production plans. A planned economy may use centralized, decentralized, participatory or Soviet-type forms of economic planning. The level of centralization or decentralization in decision-making and participation depends on the specific type of planning mechanism employed.

Socialist states based on the Soviet model have used central planning, although a minority such as the former Socialist Federal Republic of Yugoslavia have adopted some degree of market socialism. Market abolitionist socialism replaces factor markets with direct calculation as the means to coordinate the activities of the various socially owned economic enterprises that make up the economy. More recent approaches to socialist planning and allocation have come from some economists and computer scientists proposing planning mechanisms based on advances in computer science and information technology.

Economics, business, accounting, and related fields often distinguish between quantities that are stocks and those that are flows. These differ in their units of measurement. A stock is measured at one specific time, and represents a quantity existing at that point in time (say, December 31, 2004), which may have accumulated in the past. A flow variable is measured over an interval of time. Therefore, a flow would be measured per unit of time (say a year). Flow is roughly analogous to rate or speed in this sense.

For example, U.S. nominal gross domestic product refers to a total number of dollars spent over a time period, such as a year. Therefore, it is a flow variable, and has units of dollars/year. In contrast, the U.S. nominal capital stock is the total value, in dollars, of equipment, buildings, and other real productive assets in the U.S. economy, and has units of dollars. The diagram provides an intuitive illustration of how the stock of capital currently available is increased by the flow of new investment and depleted by the flow of depreciation.

In economics, aggregate demand (AD) or domestic final demand (DFD) is the total demand for final goods and services in an economy at a given time. It is often called effective demand, though at other times this term is distinguished. This is the demand for the gross domestic product of a country. It specifies the amount of goods and services that will be purchased at all possible price levels. Consumer spending, investment, corporate and government expenditure, and net exports make up the aggregate demand.

The aggregate demand curve is plotted with real output on the horizontal axis and the price level on the vertical axis. While it is theorized to be downward sloping, the Sonnenschein–Mantel–Debreu results show that the slope of the curve cannot be mathematically derived from assumptions about individual rational behavior. Instead, the downward sloping aggregate demand curve is derived with the help of three macroeconomic assumptions about the functioning of markets: Pigou's wealth effect, Keynes' interest rate effect and the Mundell–Fleming exchange-rate effect. The Pigou effect states that a higher price level implies lower real wealth and therefore lower consumption spending, giving a lower quantity of goods demanded in the aggregate. The Keynes effect states that a higher price level implies a lower real money supply and therefore higher interest rates resulting from relevant market equilibrium condition, in turn resulting in lower investment spending on new physical capital and hence a lower quantity of goods being demanded in the aggregate.