42,772 articles
InChI
InChI, or International Chemical Identifier, is a non-proprietary, machine-readable string that uniquely represents a chemical substance, developed under IUPAC at NIST between 2000 and 2004.
Incidence algebra
An incidence algebra is an associative algebra attached to a locally finite partially ordered set, introduced systematically by Gian-Carlo Rota in 1964 as the home of Möbius inversion.
Incidence matrix
An incidence matrix is a matrix recording which elements of one set are incident with elements of another, with rows for vertices and columns for edges.
Incircle
The incircle, or inscribed circle, of a triangle is the unique circle inside it tangent to all three sides, with center the incenter and radius the inradius r, satisfying K = rs.
Incised valley
An incised valley is a valley cut by a river into coastal-plain strata after a sea-level fall, later filled with sediment during renewed sea-level rise.
Inclined plane
An inclined plane is a flat surface tilted at an angle, used as a ramp to raise or lower objects with less force than a vertical lift.
Inclusion–exclusion principle
The inclusion–exclusion principle, or sieve principle, is a combinatorial counting formula giving the size of a union of finite sets via an alternating sum of intersections.
Incoherent broadband cavity-enhanced absorption spectroscopy
Incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) is an optical technique for detecting trace gases, first reported in 2003, that uses a broadband lamp or LED and a mirror cavity to achieve long path lengths.
Incoherent scatter
Incoherent scatter is a ground-based radar technique measuring electron density, temperatures, and plasma drift throughout the ionosphere; it remains the only ground-based technique observing full-altitude profiles, proposed by W. E. Gordon in 1958.
Income in India
Income in India is measured nationally by MoSPI through gross and net national income and per capita figures, with per capita net national income at ₹208,090 in 2025-26.
Income in the United Kingdom
Income in the United Kingdom is measured chiefly as household disposable income. Median income was £36,700 in 2024, with large gaps between regions and between rich and poor.
Incommensurability (philosophy of science)
Incommensurability is the thesis, introduced into philosophy of science by Thomas Kuhn and Paul Feyerabend in 1962, that successive scientific theories may share no common measure, making some comparisons fail.
Incomplete block design
An incomplete block design is an experimental design in which each block receives only a subset of treatments, used when blocks cannot hold all treatments.
Incomplete gamma function
The incomplete gamma functions γ(a,z) and Γ(a,z) are the lower and upper parts of the gamma integral, used in statistics as the gamma distribution's cumulative probabilities.
Incomplete LU factorization
An incomplete LU factorization (ILU) approximates a sparse matrix as LU plus a discarded remainder R, keeping factors sparse and serving mainly as a preconditioner for Krylov methods like GMRES.
Incompressible flow
Incompressible flow is fluid motion in which each fluid element keeps its density as it moves, applying to essentially all liquid flows and low-speed gas flows.
Incorporated Research Institutions for Seismology
Incorporated Research Institutions for Seismology (IRIS) was a US university consortium, supported by the National Science Foundation since 1984, that merged with UNAVCO in 2023 to form the EarthScope Consortium.
Indapamide
Indapamide is an oral thiazide-like diuretic developed at Servier in France and introduced in 1971, used to treat hypertension and fluid retention in heart failure.
Indecomposable distribution
An indecomposable distribution, also called an indecomposable probability distribution, is one that cannot be written as a convolution of two non-degenerate distributions, like prime numbers.
Indene
Indene (C₉H₈) is a bicyclic aromatic hydrocarbon, a benzene ring fused with cyclopentene, and the first pure PAH detected in interstellar space, in TMC-1 in 2021.
Indentation size effect
The indentation size effect (ISE) is the increase in measured hardness as indentation size decreases, becoming significant below about 1 μm depth and commonly modeled by Nix and Gao's 1998 dislocation-based theory.
Indentation testing
Indentation testing, or the indentation test, presses a hard indenter of controlled geometry into a material's surface, measuring hardness, elastic modulus, creep, and stress relaxation from resistance to penetration.
Independence (probability theory)
Independence in probability theory is the property that one event's occurrence does not change the probability of another, formalized as P(A ∩ B) = P(A) · P(B).
Independence of random variables
Independence of random variables is the property that their joint distribution factors into the product of their marginals, so knowing one tells nothing about the others.
Independence polynomial
The independence polynomial, also known as the independent set polynomial or stable set polynomial, is the graph polynomial that counts a graph's independent sets by size.
Independence property (model theory)
The independence property in model theory is a combinatorial property of formulas, isolated by Shelah as a dividing line marking the boundary of NIP, or dependent, theories.
Independence test (statistics)
An independence test, or independence testing, is a statistical hypothesis test assessing whether two variables are statistically independent, using methods such as chi-squared, distance covariance, and HSIC.
Independent and identically distributed random variables
Independent and identically distributed (i.i.d. or IID) random variables are mutually independent variables that all follow the same probability distribution, modeled on repeated throws of a die.
Independent modal space control
Independent modal space control is a vibration control method that designs a separate feedback controller for each mode of a flexible structure, developed by Leonard Meirovitch from 1976.
Independent set (graph theory)
An independent set, also called a coclique or anticlique, is a set of vertices in a graph with no edges between any pair; the largest such set is the independence number.