6,052 articles
Quasi-maximum likelihood estimation
Quasi-maximum likelihood estimation (QML, or pseudo maximum likelihood, PML) is a statistical method that maximizes a convenient likelihood even when the assumed distribution is wrong.
Quasi-Newton method
A quasi-Newton method, also called a variable metric method, is an optimization algorithm that minimizes a differentiable function by approximating the Hessian from successive gradients.
Quasi-stationarity in branching processes
Quasi-stationarity in branching processes studies quasi-stationary distributions on the non-extinct states of a branching process conditioned on survival, including the Yaglom limit for Galton–Watson processes and applications in ecology and epidemiology.
Quasigroup
A quasigroup is a set with a binary operation in which division is always possible in both directions, like a group without needing associativity or an identity.
Quaternion
Quaternions, also called Hamiltonian quaternions, are four-dimensional numbers discovered by William Rowan Hamilton in Dublin in 1843, now the standard way to represent 3D rotations without gimbal lock.
Quaternion group
The quaternion group Q8 is the eight-element nonabelian group of unit quaternions, one of the two nonabelian groups of order 8, alongside the dihedral group D4.
Quaternions and spatial rotation
Quaternions and spatial rotation is the use of quaternions, four-dimensional numbers invented by William Rowan Hamilton in 1843, to represent rotations of objects in three-dimensional space.
Queueing theory
Queueing theory, also known as teletraffic queuing theory, is the mathematical study of waiting lines, begun by Agner Krarup Erlang's 1909 work on telephone traffic in Copenhagen.
Quickest change detection
Quickest change detection (QCD) is the sequential statistical problem of detecting an abrupt change in a data stream's distribution as soon as possible, balancing detection delay against a false alarm budget.
Quintic equation
A quintic equation is a polynomial equation of degree five. Unlike lower-degree equations, the general quintic cannot be solved by radicals, as proved by Abel and Galois.
Quota sampling
Quota sampling is a non-probability survey method in which the sample is divided into quotas for demographic subpopulations, filled through non-random selection. George Gallup introduced it in 1936.
Quotient
A quotient is the result of dividing one number by another; in Euclidean division of 41 by 7, the quotient is 5 with remainder 6.
Quotient group
A quotient group, also called a factor group, is a group built from a group G and a normal subgroup N by treating the cosets of N as elements.
Quotient module
A quotient module, also called a factor module, is the module analog of a quotient group: the cosets M/N of a submodule N, with well-defined addition and scalar multiplication.
Quotient ring
A quotient ring, also called a factor ring or residue class ring, is a ring built from a ring R and an ideal I, generalizing modular arithmetic.
Quotient rule
The quotient rule is a differential calculus formula giving the derivative of a quotient of two differentiable functions, (f/g)' = (f'g − fg')/g², valid wherever the denominator g is nonzero.
Quotient set
A quotient set is the set of all equivalence classes of a set under an equivalence relation, so equivalence becomes equality, as in the integers modulo n.
Quotient space (linear algebra)
The quotient space V/W of a vector space V by a subspace W is the vector space of cosets v + W, formed by collapsing W to zero.
Quotient stack
A quotient stack, also called a quotient algebraic stack, is an algebraic stack of the form [X/G], recording orbits and stabilizers of a group action.
R (programming language)
R, also known as GNU S, is a free programming language for statistical computing and graphics, created by Ross Ihaka and Robert Gentleman in New Zealand.
Radar chart
A radar chart, also known as a spider chart or star plot, displays multivariate data on axes radiating from a common origin, joined into a closed polygon.
Radhanath Sikdar (রাধানাথ শিকদার)
Radhanath Sikdar (রাধানাথ শিকদার) was a Bengali mathematician and surveyor who, as Chief Computer of the Great Trigonometrical Survey, calculated in 1852 that Peak XV, later Mount Everest, was the world's highest mountain.
Radical center (geometry)
The radical center, also called the power center, of three circles is the point where the three pairwise radical axes meet, existing whenever the circle centers are not collinear.
Radical of an ideal
The radical of an ideal I in a commutative ring, written √I, is the set of elements some positive power of which lies in I; it is itself an ideal containing I.
Radius
A radius is the straight line from the center of a circle to any point on its circumference, equal to half the diameter and denoted r.
Radius of convergence
The radius of convergence, or interval of convergence, of a power series is the number R within which the series converges, equal to the distance to the nearest singularity.
Radius of curvature
The radius of curvature of a curve at a point is the radius of the circle that best approximates the curve there, equal to one over the curvature.
Radix
The radix, also called the number base or numeral base, is the count of distinct digits a positional numeral system uses, such as 10 for decimal or 2 for binary.
Radon measure
A Radon measure is a Borel measure on a Hausdorff space that is locally finite and inner regular, meaning every Borel set is approximated by compact subsets; Johann Radon introduced it in 1913.
Radon transform
The Radon transform is an integral transform mapping a function to its integrals over lines or hyperplanes, introduced by Johann Radon in 1917 and central to CT image reconstruction.