A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.
Type to find tags: 
automorphicforms× 309
a wellbehaved function from a topological group G to the complex numbers (or complex vector space) which is invariant under the action of a discrete subgroup \Gamma \subset G o…

it.informationtheory× 303
Covers theoretical and experimental aspects of information theory and coding.

ordertheory× 300 
abstractalgebra× 296
Do NOT use this tag. Instead you could consider gr.grouptheory, ac.commutativealgebra, ra.ringsandalgebras or various more specific tags.

schemes× 293
the geometrical study of solutions of algebraic systems of equations, not only over the real/complex numbers, but also over integer numbers (and more generally o…

etalecohomology× 289
the étale cohomology groups of an algebraic variety or scheme are algebraic analogues of the usual cohomology groups with finite coefficients of a topological space, introduced by Grothendieck in orde…

randommatrices× 286
Statistics of spectral properties of matrixvalued random variables.

galoisrepresentations× 285
frequently used when the Gmodule is a vector space over a field or a free module over a ring, but can also be used as a synonym for Gmodule. The study of Galois mod…

quantumgroups× 284
Questions about algebraic structures known as quantum groups, and their categories of representations. Quasitriangular Hopf algebras and their Drinfel'd twists, triangular Hopf algebras, $C^\star$ qua…

topologicalgroups× 283
a group $G$ together with a topology on the elements of $G$ such that the group operation and group inverse function are both continuous (with respect to the topology).

stacks× 281 
derivedcategory× 281
For questions about the derived categories of various abelian categories and questions regarding the derived category construction itself.

modules× 279
For questions on modules over rings.

axiomofchoice× 277
An important and fundamental axiom in set theory sometimes called Zermelo's axiom of choice. It was formulated by Zermelo in 1904 and states that, given any set of mutually disjoint nonempty sets, the…

additivecombinatorics× 273
Questions on the subject additive combinatorics, also known as arithmetic combinatorics, such as questions on: additive bases, sum sets, inverse sum set theorems, sets with small doubling, Sidon sets,…

3manifolds× 273 
fields× 268
Fields as algebraic objects. For vector and tensor fields, use eg. [dg.differentialgeometry]. For physical fields, use eg. [mp.mathematicalphysics] or [quantumfieldtheory].

matrixanalysis× 268
The study of the properties of real and complex matrices that are more close to analysis and operator theory. For instance: the properties of positive definite matrices, matrix inequalities, perturbat…

descriptivesettheory× 266
the study of definable subsets of Polish spaces, where definable is taken to mean from the Borel or projective hierarchies. Other topics include infinite games and determinac…

commutativerings× 263 
quadraticforms× 260  projectivegeometry× 260 
bigpicture× 259
Questions designed to get an overview of a specific subject or body of results or to understand the relations among similar definitions, techniques or concepts appearing in different subfields of mat…

singularitytheory× 259 
noncommutativealgebra× 255 
noncommutativegeometry× 252
Noncommutative geometry in the sense of Connes and beyond: noncommutative algebras viewed as functions on a noncommutative space.

linearprogramming× 250
the study of optimizing a linear function over a set of linear inequalities. The Simplex Method, Ellipsoid Method and Interior Point Method are popular algorithms to solve linea…

intuition× 250
Questions asking for the intuition behind some definition, conjecture, proof etc. In other words, questions designed to improve or to acquire understanding on a conceptual or intuitive level, as oppos…

topostheory× 249  markovchains× 248 
hopfalgebras× 246
a vector space $H$ over a field $k$ endowed with an associative product $\times:H\otimes_k H\to H$ and a coassociative coproduct $\Delta:H\to H\otimes_k H$ which is a morphism of alg…

convexoptimization× 246
Optimization with convex constraints and convex objectives; notions related to convex optimization such as subgradients, normal cones, separating hyperplanes

vonneumannalgebras× 246
Subtag of [tag:oa.operatoralgebras] for questions about von Neumann algebras, that is, weak operator topology closed, unital, *subalgebras of bounded operators on a Hilbert space.

algebraicktheory× 245  approximationtheory× 230 
hilbertspaces× 230
a real or complex vector space endowed with an inner product such that $H$ is a complete metric space when endowed with the norm induced by this inner product.
