# Second boundary value problem

One of the boundary value problems (cf. Boundary value problem, partial differential equations) for partial differential equations. For example, let there be given a second-order elliptic equation

$$\tag{* } Lu = \sum _ {i, j = 1 } ^ { n } a _ {ij} ( x) \frac{\partial ^ {2} u ( x) }{\partial x _ {i} \partial x _ {j} } + \sum _ {i = 1 } ^ { n } b _ {i} ( x) \frac{\partial u ( x) }{\partial x _ {i} } +$$

$$+ c ( x) u ( x) = f ( x),$$

where $x = ( x _ {1} \dots x _ {n} )$, $n \geq 2$, in a bounded domain $\Omega$, with a normal at each point of the boundary $\Gamma$. The second boundary value problem for equation (*) in $\Omega$ is the following problem: Out of the set of all solutions of equation (*), isolate those solutions which have, at all boundary points, derivatives with respect to the interior normal $N$ and which satisfy the condition

$$\left . \frac{\partial u ( x, t) }{\partial N ( x) } \right | _ {x \in \Gamma } = \phi ( x),$$

where $\phi ( x)$ is a given function. The second boundary value problem is also known as the Neumann problem.

How to Cite This Entry:
Second boundary value problem. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Second_boundary_value_problem&oldid=48639
This article was adapted from an original article by A.K. Gushchin (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article