Boundary (topology) - Wikipedia
https://en.wikipedia.org/wiki/Boundary_(topology)In topology and mathematics in general, the boundary of a subset S of a topological space X is the set of points which can be approached both from S and from the outside of S. More precisely, it is the set of points in the closure of not belonging to the interior of An element of the boundary of is called a boundary point of The term boundary operation refers to finding or taking the boundary o…
Boundary value problem - Wikipedia
https://en.wikipedia.org/wiki/Boundary_value_problemIn mathematics, in the field of differential equations, a boundary value problem is a differential equation together with a set of additional constraints, called the boundary conditions. A solution to a boundary value problem is a solution to the differential equation which also satisfies the boundary conditions. Boundary value problems arise in several branches of physics as any physical …