Optimal controlOptimal control theory is a branch of mathematical optimization that deals with finding a control for a dynamical system over a period of time such that an objective function is optimized. It has numerous applications in science, engineering and operations research. For example, the dynamical system might be a spacecraft with controls corresponding to rocket thrusters, and the objective might be to reach the moon with minimum fuel expenditure.
External debtA country's gross external debt (or foreign debt) is the liabilities that are owed to nonresidents by residents. The debtors can be governments, corporations or citizens. External debt may be denominated in domestic or foreign currency. It includes amounts owed to private commercial banks, foreign governments, or international financial institutions such as the International Monetary Fund (IMF) and the World Bank. External debt measures an economy's obligations to make future payments and, therefore, is an indicator of a country's vulnerability to solvency and liquidity problems.
Zero interest-rate policyZero interest-rate policy (ZIRP) is a macroeconomic concept describing conditions with a very low nominal interest rate, such as those in contemporary Japan and in the United States from December 2008 through December 2015. ZIRP is considered to be an unconventional monetary policy instrument and can be associated with slow economic growth, deflation and deleverage. Under ZIRP, the central bank maintains a 0% nominal interest rate. The ZIRP is an important milestone in monetary policy because the central bank is typically no longer able to reduce nominal interest rates.
SustainabilitySustainability is a social goal for people to co-exist on Earth over a long time. Specific definitions of this term are disputed and have varied with literature, context, and time. Experts often describe sustainability as having three dimensions (or pillars): environmental, economic, and social, and many publications emphasize the environmental dimension. In everyday use, sustainability often focuses on countering major environmental problems, including climate change, loss of biodiversity, loss of ecosystem services, land degradation, and air and water pollution.
Procyclical and countercyclical variablesProcyclical and countercyclical variables are variables that fluctuate in a way that is positively or negatively correlated with business cycle fluctuations in gross domestic product (GDP). The scope of the concept may differ between the context of macroeconomic theory and that of economic policy–making. The concept is often encountered in the context of a government's approach to spending and taxation.
Bellman equationA Bellman equation, named after Richard E. Bellman, is a necessary condition for optimality associated with the mathematical optimization method known as dynamic programming. It writes the "value" of a decision problem at a certain point in time in terms of the payoff from some initial choices and the "value" of the remaining decision problem that results from those initial choices. This breaks a dynamic optimization problem into a sequence of simpler subproblems, as Bellman's “principle of optimality" prescribes.
Greek government-debt crisisGreece faced a sovereign debt crisis in the aftermath of the financial crisis of 2007–2008. Widely known in the country as The Crisis (I Krísi), it reached the populace as a series of sudden reforms and austerity measures that led to impoverishment and loss of income and property, as well as a small-scale humanitarian crisis. In all, the Greek economy suffered the longest recession of any advanced mixed economy to date. As a result, the Greek political system has been upended, social exclusion increased, and hundreds of thousands of well-educated Greeks have left the country.
Sengoku periodThe Sengoku period is the period in Japanese history in which civil wars and social upheavals took place almost continuously in the 15th and 16th centuries. Though the Ōnin War (1467) is generally chosen as the Sengoku period's start date, there are many competing historiographies for its end date, ranging from 1568, the date of Oda Nobunaga's march on Kyoto, to the suppression of the Shimabara Rebellion in 1638, deep into what is traditionally considered the Edo period.
Muromachi periodThe Muromachi period or Muromachi era, also known as the Ashikaga period or Ashikaga era, is a division of Japanese history running from approximately 1336 to 1573. The period marks the governance of the Muromachi or Ashikaga shogunate ( or ), which was officially established in 1338 by the first Muromachi shōgun, Ashikaga Takauji, two years after the brief Kenmu Restoration (1333–1336) of imperial rule was brought to a close. The period ended in 1573 when the 15th and last shogun of this line, Ashikaga Yoshiaki, was driven out of the capital in Kyoto by Oda Nobunaga.
Edo periodThe Edo period or Tokugawa period is the period between 1603 and 1867 in the history of Japan, when Japan was under the rule of the Tokugawa shogunate and the country's 300 regional daimyo. Emerging from the chaos of the Sengoku period, the Edo period was characterized by economic growth, strict social order, isolationist foreign policies, a stable population, perpetual peace, and popular enjoyment of arts and culture, colloquially referred to as Oedo.
