The subject of the paper is the
variational problem of Lagrange with an inequality in the form (a) ϕ(x,y) ≧ 0 or (b)
ϕ(x,y,y′) ≧ 0. The question of existence and uniqueness of the continuation of a
minimizing arc is investigated at points of the boundary ϕ = 0. Various phenomena,
including splitting of extremals, dead-end, entry into, and exit from the
boundary, are treated and the conditions for their occurrence are derived.
The nature of the continuation is related to the “index” associated with an
extremal.
An appendix extends the results to a control problem of the Mayer
type.
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