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× 306
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× 301
Covers theoretical and experimental aspects of information theory and coding.

ordertheory× 296 
abstractalgebra× 295
Do NOT use this tag. Instead you could consider gr.grouptheory, ac.commutativealgebra, ra.ringsandalgebras or various more specific tags.

schemes× 291
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× 288
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× 284
Statistics of spectral properties of matrixvalued random variables.

galoisrepresentations× 283
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…

topologicalgroups× 281
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× 279 
modules× 279
For questions on modules over rings.

quantumgroups× 277
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…

axiomofchoice× 274
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…

3manifolds× 272 
derivedcategory× 272
For questions about the derived categories of various abelian categories and questions regarding the derived category construction itself.

fields× 267
Fields as algebraic objects. For vector and tensor fields, use eg. [dg.differentialgeometry]. For physical fields, use eg. [mp.mathematicalphysics] or [quantumfieldtheory].

additivecombinatorics× 267
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,…

descriptivesettheory× 264
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…

matrixanalysis× 264
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…

commutativerings× 260 
singularitytheory× 258 
bigpicture× 257
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…

projectivegeometry× 257  quadraticforms× 256 
noncommutativealgebra× 253 
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…

noncommutativegeometry× 248
Noncommutative geometry in the sense of Connes and beyond: noncommutative algebras viewed as functions on a noncommutative space.

topostheory× 248 
linearprogramming× 247
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…

algebraicktheory× 244 
hopfalgebras× 243
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…

vonneumannalgebras× 243
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.

markovchains× 242 
convexoptimization× 242
Optimization with convex constraints and convex objectives; notions related to convex optimization such as subgradients, normal cones, separating hyperplanes

approximationtheory× 227 
hilbertspaces× 226
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.
