Does this space enjoy Schur property? (proofcheck)
up vote
0
down vote
favorite
I need to know if the following reasoning is correct, if there is someone so kind to check it.
Let $mathbb{T}^d=mathbb{R}^d/mathbb{Z}^d$ be the d-dimensional thorus and consider the inhomogeneous Sobolev spaces $H^alpha$, $alphainmathbb{R}$, defined in terms of Fourier series by
$$H^alpha = left{f=sum_{kinmathbb{Z}^d} f_k, e_k, f_kinmathbb{C} Big| Vert fVert_{H^alpha}^2:=sum_k vert f_kvert^2(1+vert kvert^2)^alpha<inftyright} $$
This is a family of Hilbert spaces such that $H^alpha$ is compactly embedded in $H^beta$ whenever $alpha>beta$. Now consider the space $H^{-}:=cap_{alpha>0} H^{-alpha}$, endowed with the topology induced by the family of seminorms ${VertcdotVert_{H^{-alpha}}}_{alpha>0}$. Since the $H^{-alpha}$ are contained each one into the other, we can actually only consider a countable amount of them, say $alpha_ndownarrow 0$ and $H^-=cap_n H^{-alpha_n}$, and write an explicit metric which induces the above topology:
$$d(f,g)=sum_n 2^{-n} dfrac{Vert f-gVert_n}{1+Vert f-gVert_n}, quad VertcdotVert_n = VertcdotVert_{H^{-alpha_n}}$$
Now I claim that this space enjoys the Schur property. Let ${f_n}_n$ be a weakly convergent sequence in $H^-$, $f_n rightharpoonup f$, then it must also be weakly convergent in $H^{-alpha_n}$ for each $n$. But since $H^{-alpha_{n+1}} $ is compactly embedded into $H^{-alpha_n}$, weak convergence in the former implies strong convergence in the latter and therefore $f_nto f$ in $H^{-alpha}$ for each $alpha$, which implies strong convergence in $H^-$ as well.
I'd just like to know if this is right since when I first considered this space I was expecting it to be reflexive, but at this point it clearly can't be.
general-topology functional-analysis sobolev-spaces
add a comment |
up vote
0
down vote
favorite
I need to know if the following reasoning is correct, if there is someone so kind to check it.
Let $mathbb{T}^d=mathbb{R}^d/mathbb{Z}^d$ be the d-dimensional thorus and consider the inhomogeneous Sobolev spaces $H^alpha$, $alphainmathbb{R}$, defined in terms of Fourier series by
$$H^alpha = left{f=sum_{kinmathbb{Z}^d} f_k, e_k, f_kinmathbb{C} Big| Vert fVert_{H^alpha}^2:=sum_k vert f_kvert^2(1+vert kvert^2)^alpha<inftyright} $$
This is a family of Hilbert spaces such that $H^alpha$ is compactly embedded in $H^beta$ whenever $alpha>beta$. Now consider the space $H^{-}:=cap_{alpha>0} H^{-alpha}$, endowed with the topology induced by the family of seminorms ${VertcdotVert_{H^{-alpha}}}_{alpha>0}$. Since the $H^{-alpha}$ are contained each one into the other, we can actually only consider a countable amount of them, say $alpha_ndownarrow 0$ and $H^-=cap_n H^{-alpha_n}$, and write an explicit metric which induces the above topology:
$$d(f,g)=sum_n 2^{-n} dfrac{Vert f-gVert_n}{1+Vert f-gVert_n}, quad VertcdotVert_n = VertcdotVert_{H^{-alpha_n}}$$
Now I claim that this space enjoys the Schur property. Let ${f_n}_n$ be a weakly convergent sequence in $H^-$, $f_n rightharpoonup f$, then it must also be weakly convergent in $H^{-alpha_n}$ for each $n$. But since $H^{-alpha_{n+1}} $ is compactly embedded into $H^{-alpha_n}$, weak convergence in the former implies strong convergence in the latter and therefore $f_nto f$ in $H^{-alpha}$ for each $alpha$, which implies strong convergence in $H^-$ as well.
I'd just like to know if this is right since when I first considered this space I was expecting it to be reflexive, but at this point it clearly can't be.
general-topology functional-analysis sobolev-spaces
add a comment |
up vote
0
down vote
favorite
up vote
0
down vote
favorite
I need to know if the following reasoning is correct, if there is someone so kind to check it.
Let $mathbb{T}^d=mathbb{R}^d/mathbb{Z}^d$ be the d-dimensional thorus and consider the inhomogeneous Sobolev spaces $H^alpha$, $alphainmathbb{R}$, defined in terms of Fourier series by
$$H^alpha = left{f=sum_{kinmathbb{Z}^d} f_k, e_k, f_kinmathbb{C} Big| Vert fVert_{H^alpha}^2:=sum_k vert f_kvert^2(1+vert kvert^2)^alpha<inftyright} $$
This is a family of Hilbert spaces such that $H^alpha$ is compactly embedded in $H^beta$ whenever $alpha>beta$. Now consider the space $H^{-}:=cap_{alpha>0} H^{-alpha}$, endowed with the topology induced by the family of seminorms ${VertcdotVert_{H^{-alpha}}}_{alpha>0}$. Since the $H^{-alpha}$ are contained each one into the other, we can actually only consider a countable amount of them, say $alpha_ndownarrow 0$ and $H^-=cap_n H^{-alpha_n}$, and write an explicit metric which induces the above topology:
$$d(f,g)=sum_n 2^{-n} dfrac{Vert f-gVert_n}{1+Vert f-gVert_n}, quad VertcdotVert_n = VertcdotVert_{H^{-alpha_n}}$$
Now I claim that this space enjoys the Schur property. Let ${f_n}_n$ be a weakly convergent sequence in $H^-$, $f_n rightharpoonup f$, then it must also be weakly convergent in $H^{-alpha_n}$ for each $n$. But since $H^{-alpha_{n+1}} $ is compactly embedded into $H^{-alpha_n}$, weak convergence in the former implies strong convergence in the latter and therefore $f_nto f$ in $H^{-alpha}$ for each $alpha$, which implies strong convergence in $H^-$ as well.
I'd just like to know if this is right since when I first considered this space I was expecting it to be reflexive, but at this point it clearly can't be.
general-topology functional-analysis sobolev-spaces
I need to know if the following reasoning is correct, if there is someone so kind to check it.
Let $mathbb{T}^d=mathbb{R}^d/mathbb{Z}^d$ be the d-dimensional thorus and consider the inhomogeneous Sobolev spaces $H^alpha$, $alphainmathbb{R}$, defined in terms of Fourier series by
$$H^alpha = left{f=sum_{kinmathbb{Z}^d} f_k, e_k, f_kinmathbb{C} Big| Vert fVert_{H^alpha}^2:=sum_k vert f_kvert^2(1+vert kvert^2)^alpha<inftyright} $$
This is a family of Hilbert spaces such that $H^alpha$ is compactly embedded in $H^beta$ whenever $alpha>beta$. Now consider the space $H^{-}:=cap_{alpha>0} H^{-alpha}$, endowed with the topology induced by the family of seminorms ${VertcdotVert_{H^{-alpha}}}_{alpha>0}$. Since the $H^{-alpha}$ are contained each one into the other, we can actually only consider a countable amount of them, say $alpha_ndownarrow 0$ and $H^-=cap_n H^{-alpha_n}$, and write an explicit metric which induces the above topology:
$$d(f,g)=sum_n 2^{-n} dfrac{Vert f-gVert_n}{1+Vert f-gVert_n}, quad VertcdotVert_n = VertcdotVert_{H^{-alpha_n}}$$
Now I claim that this space enjoys the Schur property. Let ${f_n}_n$ be a weakly convergent sequence in $H^-$, $f_n rightharpoonup f$, then it must also be weakly convergent in $H^{-alpha_n}$ for each $n$. But since $H^{-alpha_{n+1}} $ is compactly embedded into $H^{-alpha_n}$, weak convergence in the former implies strong convergence in the latter and therefore $f_nto f$ in $H^{-alpha}$ for each $alpha$, which implies strong convergence in $H^-$ as well.
I'd just like to know if this is right since when I first considered this space I was expecting it to be reflexive, but at this point it clearly can't be.
general-topology functional-analysis sobolev-spaces
general-topology functional-analysis sobolev-spaces
asked Nov 14 at 21:10
Lucio
477215
477215
add a comment |
add a comment |
active
oldest
votes
active
oldest
votes
active
oldest
votes
active
oldest
votes
active
oldest
votes
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f2998824%2fdoes-this-space-enjoy-schur-property-proofcheck%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown