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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Representation theory studies (among else) representations of groups by finite matrices. The non-commutative analog of classical Fourier transforms.
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the branch of functional analysis that focuses on bounded linear operators, but it includes closed operators and nonlinear operators. Operator theory is also concerned with the stu…
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Questions on basic arithmetic involving numerical quantities only. Questions involving variable values (other than the result of the operation) should be placed under the (algebra-precalculus) tag.
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For questions on manifolds of dimension $n$, a topological space that near each point resembles $n$-dimensional Euclidean space.
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for questions involving vectors, which are elements of vector fields.
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Questions about the properties of functions of the form $\sum_{n=0}^{\infty}a_n x^n$, where the $a_n$ are real or complex numbers, and $x$ is real or complex (or more generally an element of a Banach …
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Questions related to the algebraic structure of algebraic integers
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the study of properties of convex sets and convex functions. For questions about optimization of convex functions over convex sets, please use the (convex-optimization) tag.
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Galois theory allows one to reduce certain problems in field theory, especially those related to field extensions, to problems in group theory. For questions about field theory and not Galois theory, …
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Coefficients involved in the Binomial Theorem. $\binom{n}{k}$ counts the subsets of size $k$ of a set of size $n$.
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For question involving Hilbert spaces, that is, complete normed spaces whose norm comes from an inner product.
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All mathematical questions about computer science, including theoretical computer science, formal methods, verification, and artificial intelligence. For questions about Turing computability, please u…
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Problems from or inspired by mathematics competitions. Questions regarding mathematics competitions.
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Questions involving improper integrals, defined as the limit of a definite integral as an endpoint of the interval of integration approaches either a specified real number or ∞ or −∞, or as both endpo…
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For requesting, clarifying, and comparing definitions of mathematical terms.
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the field dealing with differentiable functions on differentiable manifolds. It is closely related to differential geometry and together they make up the geometric theory of d…
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For question involving exponential functions and questions on exponential growth or decay.
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Questions regarding the Taylor series expansion of univariate and multivariate functions, including coefficients and bounds on remainders. A special case is also known as the Maclaurin series.
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for questions about divisibility, that is, determining when one thing is a multiple of another thing.
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a complete normed vector space: A vector space equipped with a norm such that every Cauchy sequence converges.
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a group (in the sense of abstract algebra) that is also a differentiable manifold, such that the group operations (addition and inversion) are smooth, and so we can study them with diff…
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For question about integration, where the theory is based on measures. So it's almost always used together with the tag [measure-theory], and its aim is to specify questions about integral, not only p…
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Questions on finding integer/rational solutions of equations.
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Questions on special functions, useful functions that frequently appear in pure and applied mathematics (usually not including "elementary" functions).
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a subset of ring such that it is possible to make a quotient ring with respect to this subset. This is the most frequent use of the name ideal, but it is used in other areas of mathemat…
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Questions on the Gaussian, or normal probability distribution, which may include multi-dimensional normal distribution.
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In dynamical systems, the motion of a particle in some geometric space, governed by some time dependent rules, is studied. The process can be discrete (where the particle jumps from point to point) or…
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geometry assuming the parallel postulate of Euclid: in a plane, given a line and a point not on that line, there is exactly one line parallel to the given line through the given point.
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For questions about Lie algebras, an algebraic structure whose main use is in studying geometric objects such as Lie groups and differentiable manifolds.
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indicates that several equations (of some type) must all hold. Do not use alone! Use in conjunction with (linear-algebra), (polynomials), (pde), (differential-equations), (inequalities) or an…
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Questions on Fourier series, the expansion of a function in terms of basis functions that satisfy an orthogonality relation. Usually, complex exponentials or sines and cosines are used.
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A branch of differential geometry dealing with Riemannian manifolds. *Riemannian manifolds* are smooth manifolds with an inner product smoothly attached to the tangent space of each point. Usually, Ri…
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The process of studying mathematics without formal instruction. _Don't_ use this tag just because you were self-studying when you came across the mathematical question you're asking; it is only for wh…
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Question about determinants, computation or theory. If $E$ is a vector space of dimension $d$, then we can compute the determinant of a $d$-uple $(v_1,\ldots,v_d)$ with respect to a basis.
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Questions on the use of algebraic techniques to prove geometric theorems.
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a function on a vector space $X$ which generalizes notion of length of vector in general vector spaces.