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Existence of optimal maps in the reflector-type problems

Wilfrid Gangbo, Vladimir Oliker (2007)

ESAIM: Control, Optimisation and Calculus of Variations

In this paper, we consider probability measures μ and ν on a d-dimensional sphere in 𝐑 d + 1 , d 1 , and cost functions of the form c ( 𝐱 , 𝐲 ) = l ( | 𝐱 - 𝐲 | 2 2 ) that generalize those arising in geometric optics where l ( t ) = - log t . We prove that if μ and ν vanish on ( d - 1 ) -rectifiable sets, if |l'(t)|>0, lim t 0 + l ( t ) = + , and g ( t ) : = t ( 2 - t ) ( l ' ( t ) ) 2 is monotone then there exists a unique optimal map To that transports μ onto ν , where optimality is measured against c. Furthermore, inf 𝐱 | T o 𝐱 - 𝐱 | > 0 . Our approach is based on direct variational arguments. In the special case when l ( t ) = - log t , existence of optimal maps...

Existence of positive radial solutions for the elliptic equations on an exterior domain

Yongxiang Li, Huanhuan Zhang (2016)

Annales Polonici Mathematici

We discuss the existence of positive radial solutions of the semilinear elliptic equation ⎧-Δu = K(|x|)f(u), x ∈ Ω ⎨αu + β ∂u/∂n = 0, x ∈ ∂Ω, ⎩ l i m | x | u ( x ) = 0 , where Ω = x N : | x | > r , N ≥ 3, K: [r₀,∞) → ℝ⁺ is continuous and 0 < r r K ( r ) d r < , f ∈ C(ℝ⁺,ℝ⁺), f(0) = 0. Under the conditions related to the asymptotic behaviour of f(u)/u at 0 and infinity, the existence of positive radial solutions is obtained. Our conditions are more precise and weaker than the superlinear or sublinear growth conditions. Our discussion is based on the fixed point...

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