WikiMili The Free Encyclopedia

This article does not cite any sources .(November 2016) (Learn how and when to remove this template message) |

In mathematics, the **three spheres inequality** bounds the norm of an harmonic function on a given sphere in terms of the norm of this function on two spheres, one with bigger radius and one with smaller radius.

**Mathematics** includes the study of such topics as quantity, structure, space, and change.

In mathematics, mathematical physics and the theory of stochastic processes, a **harmonic function** is a twice continuously differentiable function *f* : *U* → **R** where *U* is an open subset of **R**^{n} that satisfies Laplace's equation, i.e.

A **sphere** is a perfectly round geometrical object in three-dimensional space that is the surface of a completely round ball.

Let be an harmonic function on . Then for all one has

where for is the sphere of radius centred at the origin and where

Here we use the following normalisation for the norm:

A **centripetal force** is a force that makes a body follow a curved path. Its direction is always orthogonal to the motion of the body and towards the fixed point of the instantaneous center of curvature of the path. Isaac Newton described it as "a force by which bodies are drawn or impelled, or in any way tend, towards a point as to a centre". In Newtonian mechanics, gravity provides the centripetal force responsible for astronomical orbits.

In mathematics, **Laplace's equation** is a second-order partial differential equation named after Pierre-Simon Laplace who first studied its properties. This is often written as

The **Liouville function**, denoted by λ(*n*) and named after Joseph Liouville, is an important function in number theory.

In differential geometry, the **Ricci curvature tensor**, named after Gregorio Ricci-Curbastro, represents the amount by which the volume of a narrow conical piece of a small geodesic ball in a curved Riemannian manifold deviates from that of the standard ball in Euclidean space. As such, it provides one way of measuring the degree to which the geometry determined by a given Riemannian metric might differ from that of ordinary Euclidean n-space. The Ricci tensor is defined on any pseudo-Riemannian manifold, as a trace of the Riemann curvature tensor. Like the metric itself, the Ricci tensor is a symmetric bilinear form on the tangent space of the manifold.

In the calculus of variations, a field of mathematical analysis, the **functional derivative** relates a change in a functional to a change in a function on which the functional depends.

In mathematics a **Hausdorff measure** is a type of outer measure, named for Felix Hausdorff, that assigns a number in [0,∞] to each set in or, more generally, in any metric space. The zero-dimensional Hausdorff measure is the number of points in the set or ∞ if the set is infinite. The one-dimensional Hausdorff measure of a simple curve in is equal to the length of the curve. Likewise, the two dimensional Hausdorff measure of a measurable subset of is proportional to the area of the set. Thus, the concept of the Hausdorff measure generalizes counting, length, and area. It also generalizes volume. In fact, there are *d*-dimensional Hausdorff measures for any *d* ≥ 0, which is not necessarily an integer. These measures are fundamental in geometric measure theory. They appear naturally in harmonic analysis or potential theory.

In quantum information theory, a **quantum channel** is a communication channel which can transmit quantum information, as well as classical information. An example of quantum information is the state of a qubit. An example of classical information is a text document transmitted over the Internet.

In mathematics, a **matrix norm** is a vector norm in a vector space whose elements (vectors) are matrices.

In probability theory and statistics, the **inverse gamma distribution** is a two-parameter family of continuous probability distributions on the positive real line, which is the distribution of the reciprocal of a variable distributed according to the gamma distribution. Perhaps the chief use of the inverse gamma distribution is in Bayesian statistics, where the distribution arises as the marginal posterior distribution for the unknown variance of a normal distribution, if an uninformative prior is used, and as an analytically tractable conjugate prior, if an informative prior is required.

**Quantum tomography** or **quantum state tomography** is the process of reconstructing the quantum state for a source of quantum systems by measurements on the systems coming from the source. The source may be any device or system which prepares quantum states either consistently into quantum pure states or otherwise into general mixed states. To be able to uniquely identify the state, the measurements must be **tomographically complete**. That is, the measured operators must form an operator basis on the Hilbert space of the system, providing all the information about the state. Such a set of observations is sometimes called a **quorum**.

The stability radius of an object at a given nominal point is the radius of the largest ball, centered at the nominal point, all of whose elements satisfy pre-determined stability conditions. The picture of this intuitive notion is this:

In mathematics, **Eisenstein integers**, occasionally also known as **Eulerian integers**, are complex numbers of the form

In atomic, molecular, and optical physics and quantum chemistry, the **molecular Hamiltonian ** is the Hamiltonian operator representing the energy of the electrons and nuclei in a molecule. This operator and the associated Schrödinger equation play a central role in computational chemistry and physics for computing properties of molecules and aggregates of molecules, such as thermal conductivity, specific heat, electrical conductivity, optical, and magnetic properties, and reactivity.

A **hydrogen-like ion** is any atomic nucleus which has one electron and thus is isoelectronic with hydrogen. These ions carry the positive charge , where is the atomic number of the atom. Examples of hydrogen-like ions are He^{+}, Li^{2+}, Be^{3+} and B^{4+}. Because hydrogen-like ions are two-particle systems with an interaction depending only on the distance between the two particles, their (non-relativistic) Schrödinger equation can be solved in analytic form, as can the (relativistic) Dirac equation. The solutions are one-electron functions and are referred to as *hydrogen-like atomic orbitals*.

In mathematics, particularly numerical analysis, the **Bramble–Hilbert lemma**, named after James H. Bramble and Stephen Hilbert, bounds the error of an approximation of a function by a polynomial of order at most in terms of derivatives of of order . Both the error of the approximation and the derivatives of are measured by norms on a bounded domain in . This is similar to classical numerical analysis, where, for example, the error of linear interpolation can be bounded using the second derivative of . However, the Bramble–Hilbert lemma applies in any number of dimensions, not just one dimension, and the approximation error and the derivatives of are measured by more general norms involving averages, not just the maximum norm.

**Learning with errors** (**LWE**) is a problem in machine learning that is conjectured to be hard to solve. Introduced by Oded Regev in 2005, it is a generalization of the parity learning problem. Regev showed, furthermore, that the LWE problem is as hard to solve as several worst-case lattice problems. The LWE problem has recently been used as a hardness assumption to create public-key cryptosystems, such as the ring learning with errors key exchange by Peikert.

**Ideal lattices** are a special class of lattices and a generalization of cyclic lattices. Ideal lattices naturally occur in many parts of number theory, but also in other areas. In particular, they have a significant place in cryptography. Micciancio defined a generalization of cyclic lattices as ideal lattices. They can be used in cryptosystems to decrease by a square root the number of parameters necessary to describe a lattice, making them more efficient. Ideal lattices are a new concept, but similar lattice classes have been used for a long time. For example cyclic lattices, a special case of ideal lattices, are used in NTRUEncrypt and NTRUSign.

In financial mathematics, a **distortion risk measure** is a type of risk measure which is related to the cumulative distribution function of the return of a financial portfolio.

In mathematics, **Katugampola fractional operators** are integral operators that generalize the *Riemann–Liouville* and the *Hadamard* fractional operators into a unique form. The **Katugampola fractional integral** generalizes both the Riemann–Liouville fractional integral and the Hadamard fractional integral into a single form and It is also closely related to the Erdelyi–Kober operator that generalizes the Riemann–Liouville fractional integral. **Katugampola fractional derivative** has been defined using the Katugampola fractional integral and as with any other fractional differential operator, it also extends the possibility of taking real number powers or complex number powers of the integral and differential operators.

**Short integer solution (SIS)** and **ring-SIS** problems are two *average*-case problems that are used in lattice-based cryptography constructions. Lattice-based cryptography began in 1996 from a seminal work by Ajtai who presented a family of one-way functions based on SIS problem. He showed that it is secure in an average case if the shortest vector problem is hard in a worst-case scenario.

- Korevaar, J.; Meyers, J. L. H. (1994), "Logarithmic convexity for supremum norms of harmonic functions",
*Bull. London Math. Soc.*,**26**(4): 353–362, doi:10.1112/blms/26.4.353, MR 1302068

In computing, a **Digital Object Identifier** or **DOI** is a persistent identifier or handle used to uniquely identify objects, standardized by the International Organization for Standardization (ISO). An implementation of the Handle System, DOIs are in wide use mainly to identify academic, professional, and government information, such as journal articles, research reports and data sets, and official publications though they also have been used to identify other types of information resources, such as commercial videos.

* Mathematical Reviews* is a journal published by the American Mathematical Society (AMS) that contains brief synopses, and in some cases evaluations, of many articles in mathematics, statistics, and theoretical computer science. The AMS also publishes an associated online bibliographic database called MathSciNet which contains an electronic version of

This page is based on this Wikipedia article

Text is available under the CC BY-SA 4.0 license; additional terms may apply.

Images, videos and audio are available under their respective licenses.

Text is available under the CC BY-SA 4.0 license; additional terms may apply.

Images, videos and audio are available under their respective licenses.