DOI: 10.68381/jca19014 ISSN: 0944-6532

A Relaxation Result for Non-Convex and Non-Coercive Simple Integrals

Massimiliano Bianchini, Giovanni Cupini

We consider the following classical autonomous variational problem: Minimize

\left\{F(u)=\int_a^b f(u(x),u'(x))\,dx\,:\,u\in AC([a,b]), u(a)=\alpha, u(b)=\beta,\,u([a,b]) \subseteq I \right\} { F ( u ) = ∫ a b f ( u ( x ) , u ′ ( x ) )   d x   :   u ∈ A C ( [ a , b ] ) , u ( a ) = α , u ( b ) = β ,   u ( [ a , b ] ) ⊆ I }
where
I I
is a real interval,
\alpha, \beta\in I α , β ∈ I
, and
f:I\times \mathbb{R}\to [0,+\infty) f : I × R → [ 0 , + ∞ )
is possibly neither continuous, nor coercive, nor convex; in particular
f(s,\cdot) f ( s , ⋅ )
may be not convex at
0 0
. Assuming the solvability of the relaxed problem, we prove under mild assumptions that the above variational problem has a solution, too.