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Chordal graph
A chordal graph, also called a triangulated or rigid circuit graph, is an undirected graph where every cycle of length greater than three has a chord.
Chow group
The Chow group of an algebraic variety, written CH k(X), is the group of algebraic cycles modulo rational equivalence, the algebraic geometer's analog of a homology group.
Chow group of a stack
The Chow group of an algebraic stack assigns to the stack its algebraic cycles modulo rational equivalence, generalizing Chow groups of schemes; the standard definitions are due to Vistoli, Edidin and Graham, Totaro, and Kresch.
Chow test
The Chow test is an econometric test of whether the coefficients of a linear regression differ between two groups, often two periods separated by a known break point.
Christian Goldbach
Christian Goldbach (1690–1764) was a Prussian jurist and amateur mathematician, secretary of the St Petersburg Academy of Sciences, best known for the Goldbach conjecture posed to Euler in 1742.
Christopher Morcom
Christopher Collan Morcom was an English schoolboy scientist at Sherborne School, best known as Alan Turing's close friend and first love; he died in 1930 at 18.
Chromatic homotopy theory
Chromatic homotopy theory is the branch of algebraic topology that studies stable homotopy theory through a filtration indexed by the height of formal group laws, named for its analogy with the electromagnetic spectrum.
Chromatic polynomial
The chromatic polynomial of a graph counts its proper colorings with k colors for every nonnegative integer k. Birkhoff introduced it in 1912 to attack the four-color problem.
Chronology of computation of π
The chronology of computation of π traces record-setting calculations of the circle's ratio, from Babylonian approximations through Archimedes and Madhava to 314 trillion digits computed in 2025.
Chua's circuit
Chua's circuit is a simple electronic circuit, invented by Leon O. Chua in 1983, that exhibits deterministic chaos and is regarded as the simplest electronic circuit to do so.
Chuan Xue
Chuan Xue is an applied mathematician who builds multiscale models of wound healing, pancreatic cancer, and bacterial chemotaxis, and received the Presidential Early Career Award in 2017.
Church encoding
Church encoding is a method of representing data values, such as booleans and natural numbers, purely as functions in the lambda calculus, devised by Alonzo Church in the 1930s.
Church–Turing thesis
The Church–Turing thesis is the claim that every effectively calculable function is computable by a Turing machine, proposed independently by Church and Turing in the 1930s.
Church's thesis (constructive mathematics)
Church's thesis (CT) in constructive mathematics asserts that every constructible function on the natural numbers is recursive, and can be adopted as an axiom of the theory.
Cichoń's diagram
Cichoń's diagram, named after the Polish mathematician Jacek Cichoń, is a diagram in set theory displaying the ZFC-provable inequalities among ten cardinal characteristics of the continuum.
Circle
A circle is the set of points in a plane at one fixed distance, the radius, from a center; its circumference is 2πr and its area is πr².
Circle graph
A circle graph is the intersection graph of chords of a circle, introduced by Even and Itai in 1971; chords become vertices, adjacent when they cross.
Circle packing
Circle packing is the arrangement of non-overlapping circles within a given boundary, some mutually tangent. The densest packing of equal circles in the plane is the hexagonal lattice, covering about 90.7%.
Circulant graph
A circulant graph is a graph whose vertices can be numbered so its adjacency matrix is a circulant matrix, equivalently a Cayley graph of a cyclic group.
Circulant matrix
A circulant matrix is an n × n matrix in which each row is the row above shifted right with wrap-around; the discrete Fourier transform diagonalizes it, enabling fast multiplication and solving by FFT.
Circular convolution
Circular convolution is a mathematical operation that convolves two finite sequences of a fixed period N with wraparound indexing, and the discrete Fourier transform turns it into pointwise multiplication.
Circular sector
A circular sector, also called a circle sector or sector of a circle, is the wedge-shaped region of a disk enclosed by two radii and the arc between them, with area proportional to its central angle.
Circular segment
A circular segment, also called a segment of a circle, is the region of a disk bounded by a chord and the arc the chord cuts off.
Circular shift
A circular shift, also called a cyclic shift or bitwise rotate, moves elements of a sequence so those falling off one end are reinserted at the other, leaving the length unchanged.
Circumference
Circumference, also called the perimeter of a circle, is the distance around its edge, equal to π times the diameter (C = πd or 2πr).
Circumscribed circle
A circumscribed circle, or circumcircle, is the unique circle passing through all three vertices of a triangle, with center called the circumcenter; every triangle has exactly one.
Cirquent calculus
Cirquent calculus is a proof-theoretic framework introduced by Giorgi Japaridze in 2006, in which proofs are built from circuit-style structures called cirquents that allow sharing of components.
Clark transformations and filtering calculus
The Clark transformation is a change of variable in nonlinear filtering, introduced by J. M. C. Clark in 1978, that makes the filter robust to rough observation paths.
Class (set theory)
A class in set theory, also called a proper class when it is not a set, is a collection defined by a property, such as the class of all sets.
Class field theory
Class field theory is the branch of algebraic number theory that describes all abelian extensions of local and global fields, centered on the reciprocity map.