Difference between revisions of "Schwarz alternating method"
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− | One of the general methods for finding a solution to the [[Dirichlet problem|Dirichlet problem]]; it allows one to obtain a solution to the Dirichlet problem for a differential equation of elliptic type in domains <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834901.png" /> that can be represented as the union of a finite number of domains <img align="absmiddle" border="0" src=" | + | One of the general methods for finding a solution to the [[Dirichlet problem|Dirichlet problem]]; it allows one to obtain a solution to the Dirichlet problem for a differential equation of elliptic type in domains <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834901.png" /> that can be represented as the union of a finite number of domains <img align="absmiddle" border="0" src="http://springer-eom-2017-live.xmachina.nethttps://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834902.png" /> in which the solution to the Dirichlet problem is already known. Studies of H.A. Schwarz (1869; see [[#References|[1]]]) and a number of later studies by other authors were dedicated to this method for finding a solution to the Dirichlet problem for the [[Laplace equation|Laplace equation]] in plane domains. The principal idea of the Schwarz alternating method as applied to the simplest case of the Laplace equation in the union of two plane domains is the following. |
Let <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.orghttps://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834903.png" /> and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834904.png" /> be two domains in the plane with non-empty intersection and such that the solution to the Dirichlet problem for the Laplace equation is known for each of them. For instance, if <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834905.png" /> and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834906.png" /> are discs, then the solution to the Dirichlet problem for each of them is given by the [[Poisson integral|Poisson integral]]. Further, let <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834907.png" /> be the union of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834908.png" /> and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834909.png" /> for which a solution to the Dirichlet problem is sought (see Fig.). Let <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349010.png" /> denote the boundary of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349011.png" />, let <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349012.png" /> denote the parts of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349013.png" /> that are in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349014.png" /> (they are interior in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349015.png" />) and let <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349016.png" /> be the remaining parts, so that <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349017.png" />. Similarly, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349018.png" /> is the boundary of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349019.png" />, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349020.png" /> are its parts that fall in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349021.png" /> (they are also interior in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349022.png" />) and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349023.png" /> are the remaining parts, that is, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349024.png" />. Then the boundary <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349025.png" /> of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349026.png" /> can be represented in the form <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349027.png" />. | Let <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.orghttps://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834903.png" /> and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834904.png" /> be two domains in the plane with non-empty intersection and such that the solution to the Dirichlet problem for the Laplace equation is known for each of them. For instance, if <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834905.png" /> and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834906.png" /> are discs, then the solution to the Dirichlet problem for each of them is given by the [[Poisson integral|Poisson integral]]. Further, let <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834907.png" /> be the union of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834908.png" /> and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s0834909.png" /> for which a solution to the Dirichlet problem is sought (see Fig.). Let <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349010.png" /> denote the boundary of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349011.png" />, let <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349012.png" /> denote the parts of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349013.png" /> that are in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349014.png" /> (they are interior in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349015.png" />) and let <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349016.png" /> be the remaining parts, so that <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349017.png" />. Similarly, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349018.png" /> is the boundary of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349019.png" />, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349020.png" /> are its parts that fall in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349021.png" /> (they are also interior in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349022.png" />) and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349023.png" /> are the remaining parts, that is, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349024.png" />. Then the boundary <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349025.png" /> of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349026.png" /> can be represented in the form <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s083/s083490/s08349027.png" />. |
Revision as of 14:31, 26 April 2017
One of the general methods for finding a solution to the Dirichlet problem; it allows one to obtain a solution to the Dirichlet problem for a differential equation of elliptic type in domains that can be represented as the union of a finite number of domains
in which the solution to the Dirichlet problem is already known. Studies of H.A. Schwarz (1869; see [1]) and a number of later studies by other authors were dedicated to this method for finding a solution to the Dirichlet problem for the Laplace equation in plane domains. The principal idea of the Schwarz alternating method as applied to the simplest case of the Laplace equation in the union of two plane domains is the following.
Let and
be two domains in the plane with non-empty intersection and such that the solution to the Dirichlet problem for the Laplace equation is known for each of them. For instance, if
and
are discs, then the solution to the Dirichlet problem for each of them is given by the Poisson integral. Further, let
be the union of
and
for which a solution to the Dirichlet problem is sought (see Fig.). Let
denote the boundary of
, let
denote the parts of
that are in
(they are interior in
) and let
be the remaining parts, so that
. Similarly,
is the boundary of
,
are its parts that fall in
(they are also interior in
) and
are the remaining parts, that is,
. Then the boundary
of
can be represented in the form
.
Figure: s083490a
Now, given a continuous function on
, one has to find a harmonic function
in
that is continuous in the closed domain
and that takes on
the values of
. The restriction of
to
can be continuously extended to the whole boundary
, and for these boundary values one finds a solution
to the Dirichlet problem in
. The values of
on
together with the values of
on
now form a continuous function on
for which a solution
to the Dirichlet problem in
is found. Further, a solution
to the Dirichlet problem in
is constructed, based on the values of
on
and
on
, etc. The sought function has the form
![]() |
and
![]() |
Using bounded solutions of the Dirichlet problem with piecewise-continuous boundary data allows one to choose the values zero on the remaining parts of the boundaries without having to worry about the continuous extension of .
A method analogous to the Schwarz alternating method (see [2]) can be applied to finding a solution to the Dirichlet problem in the intersection of two domains and
, if its solutions for
and
are known.
Schwarz' alternating method is also used to solve boundary value problems of a more general nature for general equations of elliptic type (including equations of an order greater than two) under certain additional conditions [3], and also in domains in space.
Schwarz' alternating method is extremely important for the construction of various harmonic functions (with pre-assigned singularities) on Riemann surfaces [4].
References
[1] | H.A. Schwarz, "Gesamm. math. Abhandl." , 2 , Springer (1890) |
[2] | C. Neumann, Ber. Verh. Sächs. Akad. Wiss. Leipzig Math.-Nat. Kl. , 22 (1870) pp. 264–321 |
[3] | L.V. Kantorovich, V.I. Krylov, "Approximate methods of higher analysis" , Noordhoff (1958) (Translated from Russian) MR0106537 Zbl 0083.35301 |
[4] | R. Nevanlinna, "Uniformisierung" , Springer (1967) MR0228671 Zbl 0152.27401 |
Comments
Recently these ideas are meeting new interest among numerical analysts. They are essentially used to solve boundary value problems on complicated domains. Such domains are decomposed in smaller and simpler ones; therefore such methods are referred to as domain decomposition methods.
See [a1], pp. 200-203, for a more subtle application of the Schwarz alternating method in the study of boundary value problems.
References
[a1] | L.L. Helms, "Introduction to potential theory" , Wiley (Interscience) (1969) |
[a2] | T.F. Chan, et al., "Domain decomposition methods for partial differential equations" , SIAM (1990) MR1064333 Zbl 0695.00026 |
Schwarz alternating method. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Schwarz_alternating_method&oldid=41211