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: 
operatortheory× 164
Spectrum, resolvent, numerical range, functional calculus, operator semigroups. Special classes of operators: compact, Fredholm, dissipative, differential, integral, pseudodifferential, etc.

matrixanalysis× 163
The study of real and complex matrices and their algebraic and analytical properties, including: eigenvalues and eigenvectors, positive definite matrices, matrix inequalities, invariant subspaces, per…

projectivegeometry× 160 
ellipticpde× 160
Questions about partial differential equations of elliptic type. Often used in combination with the toplevel tag ap.analysisofpdes.

stablehomotopy× 160  manifolds× 159  algebraicsurfaces× 157  approximationtheory× 156 
mathphilosophy× 156  birationalgeometry× 150 
computationalgeometry× 148
Using computers to solve geometric problems. Questions with this tag should typically have at least one other tag indicating what sort of geometry is involved, such as ag.algebraicgeometry or mg.metr…

hilbertspaces× 148 
euclideangeometry× 142  semigroups× 142 
riemannzetafunction× 142
the function of one complex variable $s$ defined by the series $\zeta(s) = \sum_{n \geq 1} \frac{1}{n^s}$ when $\operatorname{Re}(s)>1$. It admits a meromorphic continuati…

randomwalk× 141 
prooftheory× 140
For question in Proof Theory, where "proofs" themselves are the object of mathematical investigation. It is not to be used to request a proof of some result.

monoidalcategories× 140 
computeralgebra× 140
Using computers to solve algebraic problems. Questions with this tag should typically include at least one other tag indicating what sort of algebraic problem is involved, such as ac.commutativealgeb…

textbookrecommendation× 140
Questions asking for recommendations of textbooks on some subject. It can be helpful to indicate whether the request is for selfstudy, for use in a course one teaches, for use accompanying a course o…

langlandsconjectures× 139
Higher reciprocity laws

zetafunctions× 135  homology× 133 
books× 133
Questions in which books play a keyrole, such as questions on antique books, ebooks, difference between various editions of a book, etc. For questions asking for recommendations of books on some sub…

universalalgebra× 131  calculusofvariations× 130 
lfunctions× 130
Questions about generalizations of the Riemann Zeta function of arithmetic interest whose definition relies on meromorphic continuation of special kinds of Dirichlet series, such as Dirichlet Lfuncti…

gm.generalmathematics× 128 
groupactions× 127  classfieldtheory× 125  intersectiontheory× 124  convexoptimization× 123 
career× 121 
differentialoperators× 121
Elliptic, parabolic and hyperbolic operators. Laplace, LaplaceBeltrami, Schrödinger, Dirac. Exterior derivative and Lie derivative operators.

graphcolorings× 117 
permutations× 116
Questions related to permutations, bijections from a finite (or sometimes infinite) set to itself.
