All articles starting with F

Function generator

A function generator is an electronic test instrument producing periodic waveforms such as sine, square, and triangle with settable frequency and amplitude, typically built on direct digital synthesis.

Function Health

Function Health is an American membership-based health testing company founded in 2021 and launched in 2023, offering 160+ lab tests, at-home draws, and clinician-written interpretations.

Function key

Function keys, also called PF keys, are the programmable F1 through F12 keys in a row at the top of most keyboards, assigned to commands by each application.

Function overloading

Function overloading, or method overloading, is a form of ad hoc polymorphism where multiple functions share one name and differ in parameter lists, with the compiler selecting which one a call refers to.

Function points

A function point is a unit for measuring the functional size of software, developed by Allan Albrecht at IBM in the late 1970s and now an international standard.

Function prototype

Function prototype: a C/C++ function declaration giving name, return type, and parameter types without a body, enabling compile-time argument checking; old-style K&R forms removed in C23.

Functional (mathematics)

In mathematics, a functional is a function whose input is a function and whose output is a number, central to the calculus of variations and functional analysis.

Functional abdominal pain syndrome

Functional abdominal pain syndrome (FAPS), renamed centrally mediated abdominal pain syndrome (CAPS) in Rome IV, is a chronic gut-brain interaction disorder with continuous abdominal pain unrelated to eating, defecation, or menses, lasting at least 6 months and limiting daily function.

Functional Airspace Block

A functional airspace block (FAB) is a volume of European airspace defined by operational requirements rather than national borders, under the EU's Single European Sky initiative.

Functional analysis

Functional analysis is the branch of mathematical analysis that studies functions and operators on infinite-dimensional spaces such as Banach and Hilbert spaces, often described as infinite-dimensional linear algebra.

Functional anorectal disorders

Functional anorectal disorders are chronic anorectal conditions not explained by structural disease, defined by the Rome IV criteria and classified as fecal incontinence, anorectal pain, and functional defecation disorders.

Functional anorectal pain

Functional anorectal pain (ICD-11 DD92.1) is pain of the rectum or anus without structural cause, classified by Rome IV as levator ani syndrome, unspecified functional anorectal pain, or proctalgia fugax.

Functional baseline

The functional baseline, called the Requirements Baseline in Air Force usage, is the first technical baseline in configuration management, documenting a system's approved performance requirements and verification.

Functional calculus (logic)

Functional calculus, or first-order predicate logic, is a formal system in which statements about individuals are proved from axioms, and the standard logical framework of mathematics.

Functional clustering

Functional clustering is a set of statistical and machine-learning methods that groups curves, trajectories, and time-varying observations into clusters by shape similarity, treating each observation as a function.

Functional completeness

Functional completeness, also called expressive adequacy, is the property of a set of logical connectives that can express every truth function; NAND and NOR are each complete alone.

Functional connectivity analysis

Functional connectivity analysis measures statistical relationships, most commonly temporal correlations, between activity in different brain regions, typically from resting-state fMRI, and is used in clinical research on brain disorders.

Functional connectivity MRI

Functional connectivity MRI, also called resting-state fMRI, is an MRI method that maps brain networks by measuring correlations of spontaneous BOLD signal fluctuations between regions, without any task or stimulus.

Functional coverage

Functional coverage is a user-defined metric in hardware verification that measures how much of a design's specification has been exercised during simulation, unlike automatically extracted code coverage.

Oct 10, 2026

Functional currency

Functional currency is the currency of the primary economic environment in which an entity operates, normally where it generates and expends cash; it is distinct from the presentation currency.

Functional decomposition

Functional decomposition is a method that breaks a complex function into simpler subfunctions computed separately and recombined by composition, fundamental in logic synthesis and FPGA design.

Oct 20, 2026

Functional defaecation disorders

Functional defaecation disorders (FDDs, Rome IV category F3; ICD-11 DD92.2) are gut-brain interaction disorders with impaired rectal evacuation, subtypes inadequate defecatory propulsion and dyssynergic defecation, diagnosed by 2 of 3 physiological tests and treated with biofeedback.

Functional dependency

A functional dependency in relational database theory, written X → Y, is a constraint where one set of attributes determines another, underpinning keys, Armstrong's axioms, and normalization.

Functional derivative

The functional derivative, also called the variational derivative, generalizes the ordinary derivative to functionals, mappings from functions to numbers, and underlies the calculus of variations and the Euler–Lagrange equation.

Functional diarrhoea

Functional diarrhoea (FDr, ICD-11 DD91.2) is a gut-brain disorder of chronic loose or watery stools in over 25% of stools without predominant abdominal pain, distinguished from IBS-D and diagnosed with limited testing.

Functional differential equation

A functional differential equation is a differential equation involving the unknown function at past or future argument values, modeling after-effect systems in physics, biology, economics, and control theory.

Functional dyspepsia

Functional dyspepsia (FD) is a gut-brain interaction disorder causing recurrent upper abdominal symptoms without structural disease, affecting 5-10% of people, diagnosed by Rome criteria, with subtypes PDS and EPS and treatments including TCAs and prokinetics.