** Complex analysis **, traditionally known as the **theory of functions of a complex variable**, is the branch of mathematics that investigates functions of complex numbers. It is useful in many branches of mathematics, including number theory and applied mathematics; as well as in physics, including hydrodynamics, thermodynamics, and electrical engineering.

- Holomorphic function
- Antiholomorphic function
- Cauchy–Riemann equations
- Conformal mapping
- Power series
- Radius of convergence
- Laurent series
- Meromorphic function
- Entire function
- Pole (complex analysis)
- Zero (complex analysis)
- Residue (complex analysis)
- Isolated singularity
- Removable singularity
- Essential singularity
- Branch point
- Principal branch
- Weierstrass–Casorati theorem
- Landau's constants
- Holomorphic functions are analytic
- Schwarzian derivative
- Analytic capacity
- Disk algebra

- Line integral
- Cauchy's integral theorem
- Cauchy's integral formula
- Residue theorem
- Liouville's theorem (complex analysis)
- Examples of contour integration
- Fundamental theorem of algebra
- Simply connected
- Winding number
- Bromwich integral
- Morera's theorem
- Mellin transform
- Kramers–Kronig relation, a. k. a. Hilbert transform
- Sokhotski–Plemelj theorem

- Amplitwist
- Antiderivative (complex analysis)
- Bôcher's theorem
- Cayley transform
- Complex differential equation
- Harmonic conjugate
- Hilbert's inequality
- Method of steepest descent
- Montel's theorem
- Periodic points of complex quadratic mappings
- Pick matrix
- Runge approximation theorem
- Schwarz lemma
- Weierstrass factorization theorem
- Mittag-Leffler's theorem
- Sendov's conjecture
- Infinite compositions of analytic functions

**Complex analysis**, traditionally known as the **theory of functions of a complex variable**, is the branch of mathematical analysis that investigates functions of complex numbers. It is useful in many branches of mathematics, including algebraic geometry, number theory, analytic combinatorics, applied mathematics; as well as in physics, including the branches of hydrodynamics, thermodynamics, and particularly quantum mechanics. By extension, use of complex analysis also has applications in engineering fields such as nuclear, aerospace, mechanical and electrical engineering.

In the field of complex analysis in mathematics, the **Cauchy–Riemann equations**, named after Augustin Cauchy and Bernhard Riemann, consist of a system of two partial differential equations which, together with certain continuity and differentiability criteria, form a necessary and sufficient condition for a complex function to be complex differentiable, that is, holomorphic. This system of equations first appeared in the work of Jean le Rond d'Alembert. Later, Leonhard Euler connected this system to the analytic functions. Cauchy (1814) then used these equations to construct his theory of functions. Riemann's dissertation on the theory of functions appeared in 1851.

In mathematics, a **holomorphic function** is a complex-valued function of one or more complex variables that is, at every point of its domain, complex differentiable in a neighborhood of the point. The existence of a complex derivative in a neighbourhood is a very strong condition, for it implies that any holomorphic function is actually infinitely differentiable and equal, locally, to its own Taylor series (*analytic*). Holomorphic functions are the central objects of study in complex analysis.

In complex analysis, the **Riemann mapping theorem** states that if *U* is a non-empty simply connected open subset of the complex number plane **C** which is not all of **C**, then there exists a biholomorphic mapping *f* from *U* onto the open unit disk

**Georg Friedrich Bernhard Riemann** was a German mathematician who made contributions to analysis, number theory, and differential geometry. In the field of real analysis, he is mostly known for the first rigorous formulation of the integral, the Riemann integral, and his work on Fourier series. His contributions to complex analysis include most notably the introduction of Riemann surfaces, breaking new ground in a natural, geometric treatment of complex analysis. His famous 1859 paper on the prime-counting function, containing the original statement of the Riemann hypothesis, is regarded as one of the most influential papers in analytic number theory. Through his pioneering contributions to differential geometry, Riemann laid the foundations of the mathematics of general relativity. He is considered by many to be one of the greatest mathematicians of all time.

In mathematics, a **conformal map** is a function that locally preserves angles, but not necessarily lengths.

In mathematics, particularly in complex analysis, a **Riemann surface** is a one-dimensional complex manifold. These surfaces were first studied by and are named after Bernhard Riemann. Riemann surfaces can be thought of as deformed versions of the complex plane: locally near every point they look like patches of the complex plane, but the global topology can be quite different. For example, they can look like a sphere or a torus or several sheets glued together.

In complex analysis, a branch of mathematics, **Morera's theorem**, named after Giacinto Morera, gives an important criterion for proving that a function is holomorphic.

**Complex dynamics** is the study of dynamical systems defined by iteration of functions on complex number spaces. **Complex analytic dynamics** is the study of the dynamics of specifically analytic functions.

In complex analysis, **Picard's great theorem** and **Picard's little theorem** are related theorems about the range of an analytic function. They are named after Émile Picard.

In mathematics, * differential of the first kind* is a traditional term used in the theories of Riemann surfaces and algebraic curves, for everywhere-regular differential 1-forms. Given a complex manifold

In mathematics, with special application to complex analysis, a *normal family* is a pre-compact subset of the space of continuous functions. Informally, this means that the functions in the family are not widely spread out, but rather stick together in a somewhat "clustered" manner. Sometimes, if each function in a normal family *F* satisfies a particular property , then the property also holds for each limit point of the set *F*.

In mathematics, a **doubly periodic function** is a function defined on the complex plane and having two "periods", which are complex numbers *u* and *v* that are linearly independent as vectors over the field of real numbers. That *u* and *v* are periods of a function *ƒ* means that

**Geometric function theory** is the study of geometric properties of analytic functions. A fundamental result in the theory is the Riemann mapping theorem.

In mathematics, **Riemann–Hilbert problems**, named after Bernhard Riemann and David Hilbert, are a class of problems that arise in the study of differential equations in the complex plane. Several existence theorems for Riemann–Hilbert problems have been produced by Mark Krein, Israel Gohberg and others.

A **complex differential equation** is a differential equation whose solutions are functions of a complex variable.

In mathematics, **singular integral operators on closed curves** arise in problems in analysis, in particular complex analysis and harmonic analysis. The two main singular integral operators, the Hilbert transform and the Cauchy transform, can be defined for any smooth Jordan curve in the complex plane and are related by a simple algebraic formula. In the special case of Fourier series for the unit circle, the operators become the classical Cauchy transform, the orthogonal projection onto Hardy space, and the Hilbert transform a real orthogonal linear complex structure. In general the Cauchy transform is a non-self-adjoint idempotent and the Hilbert transform a non-orthogonal complex structure. The range of the Cauchy transform is the Hardy space of the bounded region enclosed by the Jordan curve. The theory for the original curve can be deduced from that of the unit circle, where, because of rotational symmetry, both operators are classical singular integral operators of convolution type. The Hilbert transform satisfies the jump relations of Plemelj and Sokhotski, which express the original function as the difference between the boundary values of holomorphic functions on the region and its complement. Singular integral operators have been studied on various classes of functions, including Hőlder spaces, L^{p} spaces and Sobolev spaces. In the case of L^{2} spaces—the case treated in detail below—other operators associated with the closed curve, such as the Szegő projection onto Hardy space and the Neumann–Poincaré operator, can be expressed in terms of the Cauchy transform and its adjoint.

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