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Difference between revisions of "Domain of influence"

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''of a point <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/d/d033/d033810/d0338101.png" /> (of a set <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/d/d033/d033810/d0338102.png" /> of points <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/d/d033/d033810/d0338103.png" />)''
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''of a point $M$ (of a set $A$ of points $M$)''
  
The set <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/d/d033/d033810/d0338104.png" /> (respectively, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/d/d033/d033810/d0338105.png" />) of all points at which the solution of a differential equation or of a set of differential equations changes as a result of a perturbation of it at the point <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/d/d033/d033810/d0338106.png" /> (or at the set <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/d/d033/d033810/d0338107.png" />). In the simplest cases of linear partial differential equations the domain of influence is independent of the solution; for most non-linear problems the domain of influence depends both on the solution itself and on the nature of the perturbations. In such a case infinitely small perturbations are considered. For hyperbolic equations, the domain of influence of the point <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/d/d033/d033810/d0338108.png" /> is often the union of the characteristic conoid (cf. [[Characteristic manifold|Characteristic manifold]]) passing through the point <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/d/d033/d033810/d0338109.png" /> and its interior; for parabolic and elliptic equations, the domain of influence of the point <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/d/d033/d033810/d03381010.png" /> is usually the domain of definition of the solution.
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The set $B(M)$ (respectively, $B(A)$) of all points at which the solution of a differential equation or of a set of differential equations changes as a result of a perturbation of it at the point $M$ (or at the set $A$). In the simplest cases of linear partial differential equations the domain of influence is independent of the solution; for most non-linear problems the domain of influence depends both on the solution itself and on the nature of the perturbations. In such a case infinitely small perturbations are considered. For hyperbolic equations, the domain of influence of the point $M$ is often the union of the characteristic conoid (cf. [[Characteristic manifold|Characteristic manifold]]) passing through the point $M$ and its interior; for parabolic and elliptic equations, the domain of influence of the point $M$ is usually the domain of definition of the solution.
  
  

Latest revision as of 21:43, 14 April 2014

of a point $M$ (of a set $A$ of points $M$)

The set $B(M)$ (respectively, $B(A)$) of all points at which the solution of a differential equation or of a set of differential equations changes as a result of a perturbation of it at the point $M$ (or at the set $A$). In the simplest cases of linear partial differential equations the domain of influence is independent of the solution; for most non-linear problems the domain of influence depends both on the solution itself and on the nature of the perturbations. In such a case infinitely small perturbations are considered. For hyperbolic equations, the domain of influence of the point $M$ is often the union of the characteristic conoid (cf. Characteristic manifold) passing through the point $M$ and its interior; for parabolic and elliptic equations, the domain of influence of the point $M$ is usually the domain of definition of the solution.


Comments

This notion is usually met in the context of initial value problems (also called Cauchy problems, cf. Cauchy problem) for first-order, or general hyperbolic, partial differential equations (cf. Differential equation, partial, of the first order; Hyperbolic partial differential equation). For a more precise discussion of the latter case see [a1], Chapt. 6 Par. 7.

A related notion is that of the domain of dependence (cf. Cauchy problem).

References

[a1] R. Courant, D. Hilbert, "Methods of mathematical physics. Partial differential equations" , 2 , Interscience (1965) (Translated from German)
How to Cite This Entry:
Domain of influence. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Domain_of_influence&oldid=31697
This article was adapted from an original article by B.L. Rozhdestvenskii (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article