Rigour

Rigour (BrE) or rigor (AmE) (see spelling differences) describes a condition of stiffness or strictness. Rigour frequently refers to a process of adhering absolutely to certain constraints, or the practice of maintaining strict consistency with certain predefined parameters. These constraints may be environmentally imposed, such as "the rigours of famine"; logically imposed, such as mathematical proofs which must maintain consistent answers; or socially imposed, such as the process of defining ethics and law.

Etymology

Rigour comes to English through old French (13th c., Modern French rigueur) meaning "stiffness", which itself is based on the Latin rigorem (nominative rigor) "numbness, stiffness, hardness, firmness; roughness, rudeness", from the verb rigere "to be stiff". The noun was frequently used to describe a condition of strictness or stiffness, which arises from a situation or constraint either chosen or experienced passively. For example, the title of the book Theologia Moralis Inter Rigorem et Laxitatem Medi roughly translates as "mediating theological morality between rigour and laxness". The book details, for the clergy, situations in which they are obligated to follow church law exactly, and in which situations they can be more forgiving yet still considered moral.Rigor mortis translates directly as the stiffness (rigour) of death (mortis), again describing a condition which arises from a certain constraint (death).

Second-order

Second-order generally indicates an extended or higher complexity. Specific uses of the term include:

in mathematics and logic

in science and engineering

in psychology and philosophy

Complex number

A complex number is a number that can be expressed in the form a + bi, where a and b are real numbers and i is the imaginary unit, that satisfies the equation i² = −1. In this expression, a is the real part and b is the imaginary part of the complex number.

Complex numbers extend the concept of the one-dimensional number line to the two-dimensional complex plane by using the horizontal axis for the real part and the vertical axis for the imaginary part. The complex number a + bi can be identified with the point (a, b) in the complex plane. A complex number whose real part is zero is said to be purely imaginary, whereas a complex number whose imaginary part is zero is a real number. In this way, the complex numbers contain the ordinary real numbers while extending them in order to solve problems that cannot be solved with real numbers alone.

As well as their use within mathematics, complex numbers have practical applications in many fields, including physics, chemistry, biology, economics, electrical engineering, and statistics. The Italian mathematician Gerolamo Cardano is the first known to have introduced complex numbers. He called them "fictitious" during his attempts to find solutions to cubic equations in the 16th century.

State space

In the theory of discrete dynamical systems, a state space is the set of values which a process can take. For example, a system in queueing theory recording the number of customers in a line would have state space {0, 1, 2, 3, ...}. State space is conceptually similar to phase space, but for discrete rather than continuous dynamical systems.

In a computer program, when the effective state space is small compared to all reachable states, this is referred to as clumping. Software such as LURCH analyzes such situations.

In games, the state space is the set of all possible configurations within the game. For instance, in backgammon, it consists of all the possible positions in which the 30 pieces can be placed, whether on the board, on the bar or in the bear-off tray. Within this state space there is the subset of positions which are valid according to the rules of backgammon. A game's total state space is often readily calculated whereas finding the subset of valid positions may be a considerable challenge. For example, a Chess board has 8x8=64 positions, and there are 32 distinct pieces, so by combination the total state space has = 1,832,624,140,942,590,534 states. However, most of those states are not valid positions. The size of a game's state space is related to its complexity.