6,052 articles
Risk matrix
A risk matrix is a risk management grid that places rated risks by likelihood and consequence, with colored cells marking unacceptable, intermediate, and acceptable risk.
Risk-neutral measure
The risk-neutral measure, also called the equivalent martingale measure, is a probability measure under which discounted asset prices are martingales, central to no-arbitrage derivative pricing.
Ritz method
The Ritz method, also known as the Rayleigh–Ritz method, is a numerical technique that approximates solutions of variational and boundary value problems by minimizing a functional over trial functions.
RMS
RMS, or root mean square, also called the quadratic mean, averages numbers by squaring them, taking the mean, and taking the square root, so sign is ignored.
Robertson–Seymour theorem
The Robertson–Seymour theorem, also called the graph minor theorem or Wagner's conjecture, states that finite graphs are well-quasi-ordered by the minor relation; Robertson and Seymour proved it from 1983 to 2004.
Robinson arithmetic
Robinson arithmetic, usually denoted Q, is a finitely axiomatized first-order theory of the natural numbers introduced by Raphael Robinson in 1950 that drops Peano arithmetic's induction schema.
Robinson–Schensted correspondence
The Robinson–Schensted correspondence, also called the Robinson–Schensted algorithm, is a bijection in combinatorics that assigns to each permutation a pair of standard Young tableaux of the same shape.
Robinson–Schensted–Knuth correspondence
The Robinson–Schensted–Knuth correspondence, or RSK algorithm, is a combinatorial bijection sending a permutation or matrix to a pair of semistandard Young tableaux of identical shape.
Robust optimization
Robust optimization is a mathematical approach to decision-making under uncertainty in which a solution is chosen to perform well against worst-case parameter values inside a prescribed uncertainty set, rather than against expected values.
Robust principal component analysis
Robust principal component analysis (RPCA) decomposes a data matrix into a low-rank component and a sparse component of grossly corrupted entries, keeping principal components intact despite outliers.
Robust regression
Robust regression, also known as robust linear regression, is a family of methods for fitting regression models that stay reliable when data contain outliers or violate the assumptions behind ordinary least squares.
Robust statistics
Robust statistics is the branch of statistics that designs estimators and tests that resist outliers and small deviations from model assumptions, pioneered by Tukey and Huber in the 1960s.
Robustness (analytical chemistry)
Robustness, also called ruggedness, in analytical chemistry is an analytical method's ability to maintain acceptable performance when operating parameters like temperature, pH, and flow rate are deliberately varied within small, realistic limits.
Roderick Joseph Little
Roderick Joseph (Rod) Little is an American biostatistician at the University of Michigan whose research on missing data shaped clinical-trials guidance, co-authoring the standard textbook with Donald Rubin.
Rogers–Ramanujan identities
The Rogers–Ramanujan identities are two equalities in q-series theory, proved by Leonard Rogers in 1894 and rediscovered by Ramanujan before 1913, relating infinite series to infinite products.
Rolle's theorem
Rolle's theorem, also known as Rolle's lemma, is a result of differential calculus: a function continuous on [a, b], differentiable inside, and equal at the endpoints has some point with zero derivative.
Roman numerals
Roman numerals are a numeric notation in which the letters I, V, X, L, C, D, and M stand for fixed values and are added together.
Root mean square
The root mean square (RMS), also called the quadratic mean, is the square root of the mean of the squares of a set of values, used for varying quantities like AC voltage.
Root of unity
A root of unity is a complex number whose some power equals 1; the n-th roots of unity form the vertices of a regular n-gon on the unit circle.
Root polytope
A root polytope is the convex hull of the roots of a root system, centrally symmetric and containing the origin, studied in Lie theory and lattice-point counting.
Root system
A root system is a finite set of vectors in a Euclidean space closed under perpendicular reflections, encoding the symmetry of semisimple Lie algebras and classified by Dynkin diagrams.
Root test
The root test, also called Cauchy's root test or the nth-root test, decides whether an infinite series converges by examining the nth roots of its terms.
Rose (mathematics)
The rose, also called the rhodonea curve, is a plane curve with polar equation r = a sin(kθ) or r = a cos(kθ), whose petal-shaped loops resemble a flower.
Rosstat
Rosstat (Росстат), formally the Federal State Statistics Service, is the federal executive body of Russia that produces official statistics; founded 25 June 1811, it has been subordinated to the Ministry of Economic Development since 2017.
ROT13
ROT13 ("rotate by 13 places") is a letter substitution scheme that shifts each letter 13 places and, being self-inverse, encodes and decodes with the same operation.
Rota's basis conjecture
Rota's basis conjecture is an open problem in matroid theory, made in 1989, that n bases of a rank-n matroid can be repartitioned into n disjoint bases.
Rota's conjecture
Rota's conjecture, posed by Gian-Carlo Rota in 1970, asserts that each finite field has only finitely many excluded minors for representable matroids; it was proved in 2013.
Rotation (mathematics)
In mathematics, a rotation, also called a coordinate rotation, is a transformation of Euclidean space that preserves distances and orientation, described in 3D by an axis and angle.
Rotation matrix
A rotation matrix is a real orthogonal square matrix, determinant 1, that rotates vectors while preserving their lengths and handedness; the n×n ones form the group SO(n).
Rotational symmetry
Rotational symmetry is the property of a figure that looks the same after being rotated about a fixed point or axis by some angle less than a full turn.