6,052 articles
Woodbury matrix identity
The Woodbury matrix identity, also known as the Sherman–Morrison–Woodbury formula or matrix inversion lemma, expresses the inverse of a matrix after a low-rank update in terms of the original inverse.
Woodin cardinal
A Woodin cardinal is a type of large cardinal in set theory, isolated by W. Hugh Woodin, defined by strong cardinals below it and central to determinacy axioms.
Word equation
A word equation is a formal equality U = V between strings of constants and variables over a finite alphabet, the free-monoid analog of a Diophantine equation.
Word problem (mathematics)
In mathematics, a word problem is either a story-like verbal problem solved by applying operations to given numbers, or a decision problem in algebra and computability theory.
World Development Indicators
World Development Indicators (WDI) is the World Bank's primary compilation of cross-country development statistics, offering about 1,600 indicators for 217 economies with data from 1960 onward and quarterly updates.
World energy supply and consumption
World energy supply and consumption, also called primary energy or total energy supply, tracks global energy use: 620 EJ in 2023, over 80% fossil, with renewables in 2025 becoming the largest source of supply growth and passing coal in electricity.
World population milestones
World population milestones are the estimated dates when human population crossed successive billion marks, from 1 billion in 1804 to 8 billion in November 2022.
Worldometer
Worldometer, known as Worldometers until 2020, is a reference website with real-time counters for world statistics; during the COVID-19 pandemic it surpassed 1 billion monthly visits.
Wronskian
The Wronskian, also called the Wronskian determinant, is the determinant of functions and their derivatives, the standard test for linear independence of solutions of linear differential equations.
X-ray transform
The X-ray transform is an integral transform that maps a function on Rn to its integrals over straight lines, and it models CT, PET, and seismic tomography.
Yamabe flow
The Yamabe flow is a geometric evolution equation, proposed by Richard Hamilton, that deforms a Riemannian metric within its conformal class toward constant scalar curvature.
Yamabe problem
The Yamabe problem asks whether every closed Riemannian manifold of dimension at least 3 admits a metric of constant scalar curvature; it was solved affirmatively by 1984.
Yangian
A Yangian is a Hopf algebra, introduced by Vladimir Drinfeld in 1985, that infinitely deforms the enveloping algebra of a simple Lie algebra and underlies the quantum Yang-Baxter equation.
Year 2038 problem
The Year 2038 problem, also called Y2K38 or the Epochalypse, is an integer overflow that will make 32-bit Unix time counters jump from 2038 back to 1901.
Yitang Zhang (张益唐)
Yitang Zhang (张益唐) is a Chinese-born mathematician who in 2013 proved that gaps between consecutive primes stay below 70 million infinitely often, a landmark in number theory.
Yoneda lemma
The Yoneda lemma is a theorem of category theory giving a natural bijection between natural transformations out of a representable functor and the value of the target functor.
Youden index
The Youden index, also called Youden's J statistic, is a diagnostic test summary measure defined as sensitivity plus specificity minus one, proposed by W. J. Youden in 1950.
Young diagram
A Young diagram, also called a Ferrers diagram, is an array of left-justified boxes representing an integer partition, central to the representation theory of the symmetric group and symmetric functions.
Young symmetrizer
A Young symmetrizer is an element of the symmetric group algebra that symmetrizes over a Young tableau's rows and antisymmetrizes over its columns, constructing every irreducible representation.
Young tableau
A Young tableau, in its standard form a Standard Young tableau, is a filling of a Young diagram with increasing rows and columns, central to symmetric function theory.
Young's inequality
Young's inequality is a pair of estimates in analysis, proven by William Henry Young in 1912, bounding a product ab by a weighted sum of powers.
Yukawa coupling
A Yukawa coupling is a symmetric trilinear form on the moduli space of a Calabi–Yau threefold, central to mirror symmetry and named after particle physics.
Yuri Matiyasevich (Юрий Владимирович Матиясевич)
Yuri Matiyasevich (Юрий Владимирович Матиясевич), born 1947 in Leningrad, is a Russian mathematician who completed the negative solution of Hilbert's tenth problem in 1970.
Z
Z, pronounced "zed," is a formal specification notation for describing computer systems using mathematics, developed at Oxford University from the late 1970s and standardized as ISO/IEC 13568:2002.
Z notation
The Z notation, also known as the Z specification language, is a formal specification language based on typed set theory and predicate logic, developed at Oxford around 1980.
Z-test
A z-test is a statistical hypothesis test whose test statistic follows a standard normal distribution under the null hypothesis, typically testing a mean with known standard deviation or a proportion.
Zakai equation
The Zakai equation, also known as the Duncan–Mortensen–Zakai equation, is a linear stochastic partial differential equation introduced by Moshe Zakai in 1969 whose solution gives the unnormalized conditional density in nonlinear filtering.
Zarankiewicz problem
The Zarankiewicz problem asks for the maximum number of edges in a bipartite graph with given part sizes that contains no complete bipartite subgraph K(s,t), and is central to extremal graph theory.
Zariski topology
The Zariski topology is the topology used in algebraic geometry, where the closed sets are solution sets of systems of polynomial equations, introduced by Oscar Zariski in 1944.
Zeckendorf's theorem
Zeckendorf's theorem states that every positive integer can be written uniquely as a sum of distinct Fibonacci numbers with no two consecutive, as in 71 = 55 + 13 + 3.