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In mathematics, a Poincaré–Steklov operator (after Henri Poincaré and Vladimir Steklov) maps the values of one boundary condition of the solution of an elliptic partial differential equation in a domain to the values of another boundary condition. Usually, either of the boundary conditions determines the solution. Thus, a Poincaré–Steklov operator encapsulates the boundary response of the system modelled by the partial differential equation. When the partial differential equation is discretized, for example by finite elements or finite differences, the discretization of the Poincaré–Steklov operator is the Schur complement obtained by eliminating all degrees of freedom inside the domain. Note that there may be many suitable different boundary conditions for a given partial differential equation and the direction in which a Poincaré–Steklov operator maps the values of one into another is given only by a convention.〔A. Bossavit, The "scalar" Poincaré–Steklov operator and the "vector" one: algebraic structures which underlie their duality. In ''Fourth International Symposium on Domain Decomposition Methods for Partial Differential Equations (Moscow, 1990), pages 19–26. SIAM, Philadelphia, PA, 1991.〕 ==Dirichlet-to-Neumann operator on a bounded domain== Consider a steady-state distribution of temperature in a body for given temperature values on the body surface. Then the resulting heat flux through the boundary (that is, the heat flux that would be required to maintain the given surface temperature) is determined uniquely. The mapping of the surface temperature to the surface heat flux is a Poincaré–Steklov operator. This particular Poincaré–Steklov operator is called the Dirichlet to Neumann (DtN) operator. The values of the temperature on the surface is the Dirichlet boundary condition of the Laplace equation, which describes the distribution of the temperature inside the body. The heat flux through the surface is the Neumann boundary condition (proportional to the normal derivative of the temperature). Mathematically, for a function harmonic in a domain , the Dirichlet-to-Neumann operator maps the values of on the boundary of to the normal derivative on the boundary of . This Poincaré–Steklov operator is at the foundation of iterative substructuring.〔Alfio Quarteroni and Alberto Valli, Domain Decomposition Methods for Partial Differential Equations, Oxford Science Publications, 1999〕 Calderón's inverse boundary problem is the problem of finding the coefficient of a divergence form elliptic partial differential equation from its Dirichlet-to-Neumann operator. This is the mathematical formulation of electrical impedance tomography. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Poincaré–Steklov operator」の詳細全文を読む スポンサード リンク
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