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.
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finitefields× 293
a field with a finite number of elements. For each prime power $q^k$, there is a unique (up to isomorphism) finite field with $q^k$ elements. Up to isomorphism, these are the only …

ellipticpde× 292
Questions about partial differential equations of elliptic type. Often used in combination with the toplevel tag ap.analysisofpdes.

ordertheory× 291 
schemes× 284
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…

abstractalgebra× 283
Do NOT use this tag. Instead you could consider gr.grouptheory, ac.commutativealgebra, ra.ringsandalgebras or various more specific tags.

etalecohomology× 282
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…

topologicalgroups× 279
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).

randommatrices× 275
Statistics of spectral properties of matrixvalued random variables.

galoisrepresentations× 274
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…

stacks× 273 
modules× 272
For questions on modules over rings.

3manifolds× 269 
axiomofchoice× 268
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…

derivedcategory× 266
For questions about the derived categories of various abelian categories and questions regarding the derived category construction itself.

fields× 263
Fields as algebraic objects. For vector and tensor fields, use eg. [dg.differentialgeometry]. For physical fields, use eg. [mp.mathematicalphysics] or [quantumfieldtheory].

additivecombinatorics× 260
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,…

quantumgroups× 259
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…

matrixanalysis× 257
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× 256 
bigpicture× 255
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…

descriptivesettheory× 255
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…

projectivegeometry× 253  quadraticforms× 251  singularitytheory× 251 
intuition× 247
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× 246  noncommutativealgebra× 245 
noncommutativegeometry× 243
Noncommutative geometry in the sense of Connes and beyond: noncommutative algebras viewed as functions on a noncommutative space.

linearprogramming× 240
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…

vonneumannalgebras× 239
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× 234  algebraicktheory× 234 
hopfalgebras× 231
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× 227
Optimization with convex constraints and convex objectives; notions related to convex optimization such as subgradients, normal cones, separating hyperplanes

approximationtheory× 225 
mathematicseducation× 217
For questions in Mathematics Education as a scientific discipline. For more handson questions on teaching Mathematics, please use the tag teaching. There is also a Stack Exchange community http://mat…
