minkowski addition of functions and quasi-concavity of solutions
TRANSCRIPT
![Page 1: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/1.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Minkowski addition of functions and
quasi-concavity of solutions to ellipticequations
Chiara Bianchiniwork in progress
in collaboration withPaolo Salani
Dipartimento di Matematica U. DiniUniversita degli Studi di Firenze
Cortona, June 2007
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 2: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/2.jpg)
The ProblemReferences
The main ingredientsMain Theorem
def. A function u : Ω ⊆ Rn → R is called quasi-concave if it has
convex super-level sets; i.e. the set
Ωt = x ∈ Rn s.t. u(x) ≥ t,
is convex for every t ∈ R.
This is equivalent to
u(
(1 − λ)x0 + λx1
)
≥ minu(x0), u(x1),
for every λ ∈ [0, 1], x0, x1.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 3: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/3.jpg)
The ProblemReferences
The main ingredientsMain Theorem
def. A function u : Ω ⊆ Rn → R is called quasi-concave if it has
convex super-level sets; i.e. the set
Ωt = x ∈ Rn s.t. u(x) ≥ t,
is convex for every t ∈ R.
This is equivalent to
u(
(1 − λ)x0 + λx1
)
≥ minu(x0), u(x1),
for every λ ∈ [0, 1], x0, x1.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 4: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/4.jpg)
The ProblemReferences
The main ingredientsMain Theorem
The problem
Here we study the Dirichlet problem
F (x , u,Du,D2u) = 0 in Ω
u = 0 on ∂Ω0
u = 1 on ∂Ω1 ,
(1.1)
where Ω = Ω0\Ω1 is a convex ring of Rn and F is a
properi.e. F (x , u, ~q,A) ≥ F (x , v , ~q,A) whenever u ≤ v ,
continuous and
(degenerate) elliptici.e. F (x , u, ~q,A) ≥ F (x , u, ~q,B) whenever A ≥ B
operator.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 5: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/5.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Problem: since the level sets of u of value 0 and 1 are bothconvex, we look for assumptions on the operator F such that thisproperty is preserved by every level sets.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 6: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/6.jpg)
The ProblemReferences
The main ingredientsMain Theorem
M. Gabriel, A result concerning convex level–surfaces ofthree–dimensional harmonic functions, (1957).J. Lewis, Capacitary functions in convex rings, (1977).L.A. Caffarelli, J. Spruck, Convexity of solutions to someclassical variational problems, (1982).B. Kawohl, Rearrangements and Convexity of Level Sets inP.D.E., (1985).N. Korevaar, Convexity of level sets for solutions to elliptic ringproblems, (1990).[...]A. Greco, Quasi-concavity for semilinear elliptic equations withnon-monotone and anisotropic nonlinearities, (2005).P. Cuoghi, P. Salani, Convexity of level sets for solutions tononlinear elliptic problems in convex rings, (2006).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 7: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/7.jpg)
The ProblemReferences
The main ingredientsMain Theorem
[CS] A. Colesanti, P. Salani, Quasiconvex envelope of afunction and convexity of level sets of solutions to ellipticequations, (2003).
[CT] P. Cardaliaguet, R. Taharaoui, On the strictconcavity of the harmonic radius in dimension N ≥ 3, (2002).
[LS] M. Longinetti, P. Salani, On the Hessian matrixand Minkowski addition of quasiconcave functions, (2006).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 8: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/8.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
Main ingredients
The main tools of our result are:
a generalization of a technique used in [CS],
which is based on the quasi-concave envelope u∗ of a functionu;
some formulae recently proved in [CT],[LS],
regarding the gradient and the Hessian matrix of theMinkowski addition uλ of quasi-concave functions.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 9: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/9.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
Main ingredients
The main tools of our result are:
a generalization of a technique used in [CS],
which is based on the quasi-concave envelope u∗ of a functionu;
some formulae recently proved in [CT],[LS],
regarding the gradient and the Hessian matrix of theMinkowski addition uλ of quasi-concave functions.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 10: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/10.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
Main ingredients
The main tools of our result are:
a generalization of a technique used in [CS],
which is based on the quasi-concave envelope u∗ of a functionu;
some formulae recently proved in [CT],[LS],
regarding the gradient and the Hessian matrix of theMinkowski addition uλ of quasi-concave functions.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 11: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/11.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
Quasi-concave envelope of a function u
Given a function u : Ω → R,
def. u∗ is the function whose superlevel sets are the convex hulls ofthe corresponding superlevel sets of u.
i.e.u∗ ≥ t := Ω∗
t = Conv(
u ≥ t)
∀t.
A function u is quasi-concave if and only if u = u∗.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 12: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/12.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
Quasi-concave envelope of a function u
Given a function u : Ω → R,
def. u∗ is the function whose superlevel sets are the convex hulls ofthe corresponding superlevel sets of u.
i.e.u∗ ≥ t := Ω∗
t = Conv(
u ≥ t)
∀t.
A function u is quasi-concave if and only if u = u∗.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 13: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/13.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
Minkowski linear combination of functions
Let ui : Ωi → R i = 1, ...,m,λ = (λ1, ..., λm) s.t. λi ≥ 0,
∑mi=1 λi = 1.
def. uλ is the function whose super-level sets Ωλt are the
Minkowski linear combination of the corresponding super-levelsets Ωi
t of ui :
Ωλt =
m∑
i=1
λiΩit , for every t ∈ R.
If u1, ..., um are quasi-concave functions then uλ isquasi-concave.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 14: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/14.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
Minkowski linear combination of functions
Let ui : Ωi → R i = 1, ...,m,λ = (λ1, ..., λm) s.t. λi ≥ 0,
∑mi=1 λi = 1.
def. uλ is the function whose super-level sets Ωλt are the
Minkowski linear combination of the corresponding super-levelsets Ωi
t of ui :
Ωλt =
m∑
i=1
λiΩit , for every t ∈ R.
If u1, ..., um are quasi-concave functions then uλ isquasi-concave.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 15: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/15.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
u∗ and uλ
Notice that, taking ui = u, i = 1, ...,m we have:
Ω∗t =
⋃
λ
Ωλt ,
u∗(x) = supλ
uλ(x).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 16: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/16.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
u∗ and uλ
Notice that, taking ui = u, i = 1, ...,m we have:
Ω∗t =
⋃
λ
Ωλt ,
u∗(x) = supλ
uλ(x).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 17: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/17.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
The strategy for the problem (1.1)
To show that the solution u is quasi-concave,
we look for conditions that imply u = u∗.
Notice that
u∗ ≥ u holds by definition,
u∗ ≤ u can be proved using a suitable comparisonprinciple, if we prove that u∗ is a subsolution of problem 1.1 inthe viscosity sense.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 18: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/18.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
The strategy for the problem (1.1)
To show that the solution u is quasi-concave,
we look for conditions that imply u = u∗.
Notice that
u∗ ≥ u holds by definition,
u∗ ≤ u can be proved using a suitable comparisonprinciple, if we prove that u∗ is a subsolution of problem 1.1 inthe viscosity sense.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 19: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/19.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
The strategy for the problem (1.1)
To show that the solution u is quasi-concave,
we look for conditions that imply u = u∗.
Notice that
u∗ ≥ u holds by definition,
u∗ ≤ u can be proved using a suitable comparisonprinciple, if we prove that u∗ is a subsolution of problem 1.1 inthe viscosity sense.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 20: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/20.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
The strategy for the problem (1.1)
To show that the solution u is quasi-concave,
we look for conditions that imply u = u∗.
Notice that
u∗ ≥ u holds by definition,
u∗ ≤ u can be proved using a suitable comparisonprinciple, if we prove that u∗ is a subsolution of problem 1.1 inthe viscosity sense.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 21: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/21.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
Can we find suitable assumptions on F that force u∗ to be aviscosity subsolution of (1.1)?
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 22: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/22.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
Some definitions: viscosity solutions
def. Given a function u we say that ϕ ∈ C 2 touches u fromabove (below) at a point x if
ϕ(x) = u(x) and, ϕ − u has a local minimum (maximum) at x .
def. A function v is a viscosity subsolution (supersolution) ofF (x , u,Du,D2u) = 0 if
for every function ϕ ∈ C 2 that touches v from above (below)at x one has
F (x , v(x), Dϕ(x), D2ϕ(x)) ≥ (≤) 0,
for every x ∈ Ω.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 23: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/23.jpg)
The ProblemReferences
The main ingredientsMain Theorem
quasi-concave envelope of functionsMinkowski addition of functionsu∗ and uλ
The strategy
Some definitions: comparison principle
def. An operator F satisfies a comparison principle if, givenu, v : Ω → R viscosity subsolution and supersolutionrespectively,
u ≤ v on bd(Ω) implies u ≤ v in Ω.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 24: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/24.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Main theorem
TheoremLet Ω = Ω0\Ω1 be a convex ring and let F (x , u, p,A) be a
proper
continuous
elliptic
operator.
Assume that Gt,θ : (x , p,A) → F(
x , t, θp, A
p3
)
is quasi-concave for
every fixed t ∈ [0, 1], θ ∈ Sn−1.If u ∈ C 2(Ω) ∩ C (Ω) is a classical solution of (1.1) such that‖Du‖ > 0 in Ω, then
u∗ is a viscosity subsolution of (1.1).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 25: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/25.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Main theorem
TheoremLet Ω = Ω0\Ω1 be a convex ring and let F (x , u, p,A) be a
proper
continuous
elliptic
operator.
Assume that Gt,θ : (x , p,A) → F(
x , t, θp, A
p3
)
is quasi-concave for
every fixed t ∈ [0, 1], θ ∈ Sn−1.If u ∈ C 2(Ω) ∩ C (Ω) is a classical solution of (1.1) such that‖Du‖ > 0 in Ω, then
u∗ is a viscosity subsolution of (1.1).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 26: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/26.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Sketch of the proof
We want to prove that: for every x ∈ Ω, for every C 2 function ϕ
that touches u∗ from above at x , then
F (x , u∗(x),Dϕ(x),D2ϕ(x)) ≥ 0,
holds.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 27: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/27.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Let x ∈ Ω, t = u∗(x)
It is known that: ∃ xi ∈ bd(Ωt), i = 1, ..., nand λ = (λ1, ..., λn) with 0 ≤ λi ≤ 1,
∑ni=1 λi = 1 such that
x =n∑
i=1
λixi and u∗(x) = u(x1) = ... = u(xn) = t.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 28: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/28.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Let x ∈ Ω, t = u∗(x)
It is known that: ∃ xi ∈ bd(Ωt), i = 1, ..., nand λ = (λ1, ..., λn) with 0 ≤ λi ≤ 1,
∑ni=1 λi = 1 such that
x =n∑
i=1
λixi and u∗(x) = u(x1) = ... = u(xn) = t.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 29: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/29.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Let x ∈ Ω, t = u∗(x)
It is known that: ∃ xi ∈ bd(Ωt), i = 1, ..., nand λ = (λ1, ..., λn) with 0 ≤ λi ≤ 1,
∑ni=1 λi = 1 such that
x =n∑
i=1
λixi and u∗(x) = u(x1) = ... = u(xn) = t.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 30: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/30.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Let us consider the Minkowski linear combination of n copies ofthe functions u with coefficients λi .
For semplicity assume that u has strictly convex level set atx0, ..., xn so, by [LS], uλ ∈ C 2 at x (the general case followsby an approximation method).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 31: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/31.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Let us consider the Minkowski linear combination of n copies ofthe functions u with coefficients λi .
For semplicity assume that u has strictly convex level set atx0, ..., xn so, by [LS], uλ ∈ C 2 at x (the general case followsby an approximation method).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 32: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/32.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Then it holds:
u∗(x) = uλ(x) = u(xi ) = t, i = 1, ..., n,
u∗(x) ≥ uλ(x) ≥ u(x) for every x ∈ Ω,
Duλ(x)
‖Duλ(x)‖=
Du(xi)
‖Du(xi )‖= θ, i = 1, ..., n.
Notice that if ϕ touches u∗ from above at x , then ϕ touches uλ
from above at x ; this implies that
ϕ(x) = u∗(x) = uλ(x) = t,
Dϕ(x) = Du∗(x) = Duλ(x),
D2ϕ(x) ≥ D2uλ(x).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 33: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/33.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Then it holds:
u∗(x) = uλ(x) = u(xi ) = t, i = 1, ..., n,
u∗(x) ≥ uλ(x) ≥ u(x) for every x ∈ Ω,
Duλ(x)
‖Duλ(x)‖=
Du(xi)
‖Du(xi )‖= θ, i = 1, ..., n.
Notice that if ϕ touches u∗ from above at x , then ϕ touches uλ
from above at x ; this implies that
ϕ(x) = u∗(x) = uλ(x) = t,
Dϕ(x) = Du∗(x) = Duλ(x),
D2ϕ(x) ≥ D2uλ(x).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 34: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/34.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Then it holds:
u∗(x) = uλ(x) = u(xi ) = t, i = 1, ..., n,
u∗(x) ≥ uλ(x) ≥ u(x) for every x ∈ Ω,
Duλ(x)
‖Duλ(x)‖=
Du(xi)
‖Du(xi )‖= θ, i = 1, ..., n.
Notice that if ϕ touches u∗ from above at x , then ϕ touches uλ
from above at x ; this implies that
ϕ(x) = u∗(x) = uλ(x) = t,
Dϕ(x) = Du∗(x) = Duλ(x),
D2ϕ(x) ≥ D2uλ(x).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 35: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/35.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
By [CT],[LS] we have:
•1
‖Duλ(x)‖=
n∑
i=1
λi
1
‖Du(xi )‖,
•D2uλ(x)
‖Duλ(x)‖3≥
n∑
i=1
λi
D2u(xi )
‖Du(xi )‖3.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 36: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/36.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
F (x , t,Dϕ(x),D2ϕ(x))
≥ F (x , t,Duλ(x),D2uλ(x))
≥ F
(
x , t,θ
∑ni=1
λi
‖u(xi )‖
,(
n∑
i=1
λi
‖Du(xi)‖
)−3(n∑
i=1
D2u(xi )
‖Du(xi )‖3
)
)
= Gt,θ
(
n∑
i=1
λixi ,
n∑
i=1
λi
1
‖Du(xi )‖,
n∑
i=1
λiD2u(xi)
)
≥ mini=1,...,n
Gt,θ(xi ,1
‖Du(xi)‖,D2u(xi ))
= mini=1,...,n
F(
xi , u(xi ),Du(xi ),D2u(xi)
)
= 0
This shows that u∗ is a viscosity subsolution of the problem (1.1).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 37: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/37.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
F (x , t,Dϕ(x),D2ϕ(x))
≥ F (x , t,Duλ(x),D2uλ(x))
≥ F
(
x , t,θ
∑ni=1
λi
‖u(xi )‖
,(
n∑
i=1
λi
‖Du(xi)‖
)−3(n∑
i=1
D2u(xi )
‖Du(xi )‖3
)
)
= Gt,θ
(
n∑
i=1
λixi ,
n∑
i=1
λi
1
‖Du(xi )‖,
n∑
i=1
λiD2u(xi)
)
≥ mini=1,...,n
Gt,θ(xi ,1
‖Du(xi)‖,D2u(xi ))
= mini=1,...,n
F(
xi , u(xi ),Du(xi ),D2u(xi)
)
= 0
This shows that u∗ is a viscosity subsolution of the problem (1.1).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 38: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/38.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
F (x , t,Dϕ(x),D2ϕ(x))
≥ F (x , t,Duλ(x),D2uλ(x))
≥ F
(
x , t,θ
∑ni=1
λi
‖u(xi )‖
,(
n∑
i=1
λi
‖Du(xi)‖
)−3(n∑
i=1
D2u(xi )
‖Du(xi )‖3
)
)
= Gt,θ
(
n∑
i=1
λixi ,
n∑
i=1
λi
1
‖Du(xi )‖,
n∑
i=1
λiD2u(xi)
)
≥ mini=1,...,n
Gt,θ(xi ,1
‖Du(xi)‖,D2u(xi ))
= mini=1,...,n
F(
xi , u(xi ),Du(xi ),D2u(xi)
)
= 0
This shows that u∗ is a viscosity subsolution of the problem (1.1).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 39: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/39.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
F (x , t,Dϕ(x),D2ϕ(x))
≥ F (x , t,Duλ(x),D2uλ(x))
≥ F
(
x , t,θ
∑ni=1
λi
‖u(xi )‖
,(
n∑
i=1
λi
‖Du(xi)‖
)−3(n∑
i=1
D2u(xi )
‖Du(xi )‖3
)
)
= Gt,θ
(
n∑
i=1
λixi ,
n∑
i=1
λi
1
‖Du(xi )‖,
n∑
i=1
λiD2u(xi)
)
≥ mini=1,...,n
Gt,θ(xi ,1
‖Du(xi)‖,D2u(xi ))
= mini=1,...,n
F(
xi , u(xi ),Du(xi ),D2u(xi)
)
= 0
This shows that u∗ is a viscosity subsolution of the problem (1.1).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 40: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/40.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
F (x , t,Dϕ(x),D2ϕ(x))
≥ F (x , t,Duλ(x),D2uλ(x))
≥ F
(
x , t,θ
∑ni=1
λi
‖u(xi )‖
,(
n∑
i=1
λi
‖Du(xi)‖
)−3(n∑
i=1
D2u(xi )
‖Du(xi )‖3
)
)
= Gt,θ
(
n∑
i=1
λixi ,
n∑
i=1
λi
1
‖Du(xi )‖,
n∑
i=1
λiD2u(xi)
)
≥ mini=1,...,n
Gt,θ(xi ,1
‖Du(xi)‖,D2u(xi ))
= mini=1,...,n
F(
xi , u(xi ),Du(xi ),D2u(xi)
)
= 0
This shows that u∗ is a viscosity subsolution of the problem (1.1).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 41: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/41.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
F (x , t,Dϕ(x),D2ϕ(x))
≥ F (x , t,Duλ(x),D2uλ(x))
≥ F
(
x , t,θ
∑ni=1
λi
‖u(xi )‖
,(
n∑
i=1
λi
‖Du(xi)‖
)−3(n∑
i=1
D2u(xi )
‖Du(xi )‖3
)
)
= Gt,θ
(
n∑
i=1
λixi ,
n∑
i=1
λi
1
‖Du(xi )‖,
n∑
i=1
λiD2u(xi)
)
≥ mini=1,...,n
Gt,θ(xi ,1
‖Du(xi)‖,D2u(xi ))
= mini=1,...,n
F(
xi , u(xi ),Du(xi ),D2u(xi)
)
= 0
This shows that u∗ is a viscosity subsolution of the problem (1.1).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 42: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/42.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
F (x , t,Dϕ(x),D2ϕ(x)) ≥
≥ F (x , t,Duλ(x),D2uλ(x))
≥ F
(
x , t,θ
∑ni=1
λi
‖u(xi )‖
,(
n∑
i=1
λi
‖Du(xi)‖
)−3(n∑
i=1
D2u(xi )
‖Du(xi )‖3
)
)
= Gt,θ
(
n∑
i=1
λixi ,
n∑
i=1
λi
1
‖Du(xi )‖,
n∑
i=1
λiD2u(xi)
)
≥ mini=1,...,n
Gt,θ(xi ,1
‖Du(xi)‖,D2u(xi ))
= mini=1,...,n
F(
xi , u(xi ),Du(xi ),D2u(xi)
)
= 0
This shows that u∗ is a viscosity subsolution of the problem (1.1).
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 43: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/43.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Examples
The Laplacian,
the p-Laplacian,
the Mean Curvature operator;
concave and homogeneous operators,
example: Pucci’s extremal operators.
Chiara Bianchini Minkowski addition and quasi-concavity
![Page 44: Minkowski addition of functions and quasi-concavity of solutions](https://reader035.vdocuments.site/reader035/viewer/2022062510/613c1a3f22e01a42d40e9c34/html5/thumbnails/44.jpg)
The ProblemReferences
The main ingredientsMain Theorem
Sketch of the proofExamples
Examples
The Laplacian,
the p-Laplacian,
the Mean Curvature operator;
concave and homogeneous operators,
example: Pucci’s extremal operators.
Chiara Bianchini Minkowski addition and quasi-concavity