In Hilbert space $ dim(operatorname{coker}(T))=dim(ker(T^{*}))$












0












$begingroup$


$H$ is a Hilbert space, and $Tin B(H)$ continuous and Fredholm operator.
Same books in definition of Fredholm use (when work in Banach space)



$operatorname{ind}(T)=dim(ker(T))-dim(operatorname{coker}(T))$



and another's (when work with Hilbert space)



$operatorname{ind}(T)=dim(ker(T))-dim(ker(T^{*}))$ , $T^{*}$ is the adjoint operator



so how can i show that



$dim(operatorname{coker}(T))=dim(ker(T^{*}))$



$operatorname{coker}(T)=H/T(H)$ and $Ker(T^{*})=(T(H))^{perp}$. so in Hilbert is true $H/T(H)approx (T(H))^{perp}$ ?



thanks










share|cite|improve this question











$endgroup$












  • $begingroup$
    you are allowed to substract the two equalities as long as all the terms are finite. I do not see the problem?
    $endgroup$
    – Picaud Vincent
    Nov 30 '18 at 23:16










  • $begingroup$
    @PicaudVincent my problem in my mind, is see the two definitions are the same, so well if we assume $T$ is Fredholm , see the boths dimensions are equal
    $endgroup$
    – user89940
    Nov 30 '18 at 23:18










  • $begingroup$
    $coker(T)=H/T(H)$ and $Ker(T^{*})=(T(H))^{perp}$. so in Hilbert is true $H/T(H)approx (T(H))^{perp}$ ?
    $endgroup$
    – user89940
    Dec 1 '18 at 0:00


















0












$begingroup$


$H$ is a Hilbert space, and $Tin B(H)$ continuous and Fredholm operator.
Same books in definition of Fredholm use (when work in Banach space)



$operatorname{ind}(T)=dim(ker(T))-dim(operatorname{coker}(T))$



and another's (when work with Hilbert space)



$operatorname{ind}(T)=dim(ker(T))-dim(ker(T^{*}))$ , $T^{*}$ is the adjoint operator



so how can i show that



$dim(operatorname{coker}(T))=dim(ker(T^{*}))$



$operatorname{coker}(T)=H/T(H)$ and $Ker(T^{*})=(T(H))^{perp}$. so in Hilbert is true $H/T(H)approx (T(H))^{perp}$ ?



thanks










share|cite|improve this question











$endgroup$












  • $begingroup$
    you are allowed to substract the two equalities as long as all the terms are finite. I do not see the problem?
    $endgroup$
    – Picaud Vincent
    Nov 30 '18 at 23:16










  • $begingroup$
    @PicaudVincent my problem in my mind, is see the two definitions are the same, so well if we assume $T$ is Fredholm , see the boths dimensions are equal
    $endgroup$
    – user89940
    Nov 30 '18 at 23:18










  • $begingroup$
    $coker(T)=H/T(H)$ and $Ker(T^{*})=(T(H))^{perp}$. so in Hilbert is true $H/T(H)approx (T(H))^{perp}$ ?
    $endgroup$
    – user89940
    Dec 1 '18 at 0:00
















0












0








0





$begingroup$


$H$ is a Hilbert space, and $Tin B(H)$ continuous and Fredholm operator.
Same books in definition of Fredholm use (when work in Banach space)



$operatorname{ind}(T)=dim(ker(T))-dim(operatorname{coker}(T))$



and another's (when work with Hilbert space)



$operatorname{ind}(T)=dim(ker(T))-dim(ker(T^{*}))$ , $T^{*}$ is the adjoint operator



so how can i show that



$dim(operatorname{coker}(T))=dim(ker(T^{*}))$



$operatorname{coker}(T)=H/T(H)$ and $Ker(T^{*})=(T(H))^{perp}$. so in Hilbert is true $H/T(H)approx (T(H))^{perp}$ ?



thanks










share|cite|improve this question











$endgroup$




$H$ is a Hilbert space, and $Tin B(H)$ continuous and Fredholm operator.
Same books in definition of Fredholm use (when work in Banach space)



$operatorname{ind}(T)=dim(ker(T))-dim(operatorname{coker}(T))$



and another's (when work with Hilbert space)



$operatorname{ind}(T)=dim(ker(T))-dim(ker(T^{*}))$ , $T^{*}$ is the adjoint operator



so how can i show that



$dim(operatorname{coker}(T))=dim(ker(T^{*}))$



$operatorname{coker}(T)=H/T(H)$ and $Ker(T^{*})=(T(H))^{perp}$. so in Hilbert is true $H/T(H)approx (T(H))^{perp}$ ?



thanks







operator-theory






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Dec 1 '18 at 0:12







user89940

















asked Nov 30 '18 at 22:03









user89940user89940

797




797












  • $begingroup$
    you are allowed to substract the two equalities as long as all the terms are finite. I do not see the problem?
    $endgroup$
    – Picaud Vincent
    Nov 30 '18 at 23:16










  • $begingroup$
    @PicaudVincent my problem in my mind, is see the two definitions are the same, so well if we assume $T$ is Fredholm , see the boths dimensions are equal
    $endgroup$
    – user89940
    Nov 30 '18 at 23:18










  • $begingroup$
    $coker(T)=H/T(H)$ and $Ker(T^{*})=(T(H))^{perp}$. so in Hilbert is true $H/T(H)approx (T(H))^{perp}$ ?
    $endgroup$
    – user89940
    Dec 1 '18 at 0:00




















  • $begingroup$
    you are allowed to substract the two equalities as long as all the terms are finite. I do not see the problem?
    $endgroup$
    – Picaud Vincent
    Nov 30 '18 at 23:16










  • $begingroup$
    @PicaudVincent my problem in my mind, is see the two definitions are the same, so well if we assume $T$ is Fredholm , see the boths dimensions are equal
    $endgroup$
    – user89940
    Nov 30 '18 at 23:18










  • $begingroup$
    $coker(T)=H/T(H)$ and $Ker(T^{*})=(T(H))^{perp}$. so in Hilbert is true $H/T(H)approx (T(H))^{perp}$ ?
    $endgroup$
    – user89940
    Dec 1 '18 at 0:00


















$begingroup$
you are allowed to substract the two equalities as long as all the terms are finite. I do not see the problem?
$endgroup$
– Picaud Vincent
Nov 30 '18 at 23:16




$begingroup$
you are allowed to substract the two equalities as long as all the terms are finite. I do not see the problem?
$endgroup$
– Picaud Vincent
Nov 30 '18 at 23:16












$begingroup$
@PicaudVincent my problem in my mind, is see the two definitions are the same, so well if we assume $T$ is Fredholm , see the boths dimensions are equal
$endgroup$
– user89940
Nov 30 '18 at 23:18




$begingroup$
@PicaudVincent my problem in my mind, is see the two definitions are the same, so well if we assume $T$ is Fredholm , see the boths dimensions are equal
$endgroup$
– user89940
Nov 30 '18 at 23:18












$begingroup$
$coker(T)=H/T(H)$ and $Ker(T^{*})=(T(H))^{perp}$. so in Hilbert is true $H/T(H)approx (T(H))^{perp}$ ?
$endgroup$
– user89940
Dec 1 '18 at 0:00






$begingroup$
$coker(T)=H/T(H)$ and $Ker(T^{*})=(T(H))^{perp}$. so in Hilbert is true $H/T(H)approx (T(H))^{perp}$ ?
$endgroup$
– user89940
Dec 1 '18 at 0:00












1 Answer
1






active

oldest

votes


















1












$begingroup$


For any closed subspace $K$ of a Hilbert space $H$, we have
$$H/Kcong K^perp.$$




Proof.



$newcommand{co}{operatorname{coker}}$Let begin{align*}Phi: & K^perpto H/K\
& hmapsto [h]end{align*}



(1) Of course, $Phi$ is linear bounded.



(2) $Phi$ is injective. Suppose $hin K^perp$ such that $Phi(h)=0$, then $hin K^perpcap K$, so $h=0$.



(3) $Phi$ is surjective. For any $hin H$, there is some $h'in K^perp$ such that $h-h'in K$, thus $Phi(h')=[h']=[h]$.



Noting that $TH$ is closed subspace in the question, $H/THcong (TH)^perp$.






share|cite|improve this answer











$endgroup$









  • 1




    $begingroup$
    thanks, so hypothesis of $T$ fredholm is needed for asume $T(X)$ is closed
    $endgroup$
    – user89940
    Dec 1 '18 at 3:10










  • $begingroup$
    For any subset $S$ of $H$, $H/overline{span{S}}=S^perp$. The very usage of $T(H)$ is closed is $T(H)=overline{span{T(H)}}$
    $endgroup$
    – C.Ding
    Dec 1 '18 at 4:13












  • $begingroup$
    A better answer has been updated.
    $endgroup$
    – C.Ding
    Dec 1 '18 at 4:23












  • $begingroup$
    the hypothesis of $T(H)$ closed is needed for definition in Hilbert version right? because in Banach version $T$ operator with finite coker have image closed. But in hilbert version say "finite dimension of $Ker(T)$ and $Ker(T^{*})$" not impliy $T(H)$ closed? like this answer math.stackexchange.com/questions/1107449/…
    $endgroup$
    – user89940
    Dec 1 '18 at 16:15








  • 1




    $begingroup$
    Yes. If you define coker of an operator $u:Xto Y$ between Banach spaces as $ker u^#$, you will also need the closedness of $uX$ in the definition of a Fredholm operator. If you define the coker of $u$ as a linear space $Y/uX$, then you need not the closedness of uX in any version.
    $endgroup$
    – C.Ding
    Dec 5 '18 at 7:53











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1 Answer
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oldest

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1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









1












$begingroup$


For any closed subspace $K$ of a Hilbert space $H$, we have
$$H/Kcong K^perp.$$




Proof.



$newcommand{co}{operatorname{coker}}$Let begin{align*}Phi: & K^perpto H/K\
& hmapsto [h]end{align*}



(1) Of course, $Phi$ is linear bounded.



(2) $Phi$ is injective. Suppose $hin K^perp$ such that $Phi(h)=0$, then $hin K^perpcap K$, so $h=0$.



(3) $Phi$ is surjective. For any $hin H$, there is some $h'in K^perp$ such that $h-h'in K$, thus $Phi(h')=[h']=[h]$.



Noting that $TH$ is closed subspace in the question, $H/THcong (TH)^perp$.






share|cite|improve this answer











$endgroup$









  • 1




    $begingroup$
    thanks, so hypothesis of $T$ fredholm is needed for asume $T(X)$ is closed
    $endgroup$
    – user89940
    Dec 1 '18 at 3:10










  • $begingroup$
    For any subset $S$ of $H$, $H/overline{span{S}}=S^perp$. The very usage of $T(H)$ is closed is $T(H)=overline{span{T(H)}}$
    $endgroup$
    – C.Ding
    Dec 1 '18 at 4:13












  • $begingroup$
    A better answer has been updated.
    $endgroup$
    – C.Ding
    Dec 1 '18 at 4:23












  • $begingroup$
    the hypothesis of $T(H)$ closed is needed for definition in Hilbert version right? because in Banach version $T$ operator with finite coker have image closed. But in hilbert version say "finite dimension of $Ker(T)$ and $Ker(T^{*})$" not impliy $T(H)$ closed? like this answer math.stackexchange.com/questions/1107449/…
    $endgroup$
    – user89940
    Dec 1 '18 at 16:15








  • 1




    $begingroup$
    Yes. If you define coker of an operator $u:Xto Y$ between Banach spaces as $ker u^#$, you will also need the closedness of $uX$ in the definition of a Fredholm operator. If you define the coker of $u$ as a linear space $Y/uX$, then you need not the closedness of uX in any version.
    $endgroup$
    – C.Ding
    Dec 5 '18 at 7:53
















1












$begingroup$


For any closed subspace $K$ of a Hilbert space $H$, we have
$$H/Kcong K^perp.$$




Proof.



$newcommand{co}{operatorname{coker}}$Let begin{align*}Phi: & K^perpto H/K\
& hmapsto [h]end{align*}



(1) Of course, $Phi$ is linear bounded.



(2) $Phi$ is injective. Suppose $hin K^perp$ such that $Phi(h)=0$, then $hin K^perpcap K$, so $h=0$.



(3) $Phi$ is surjective. For any $hin H$, there is some $h'in K^perp$ such that $h-h'in K$, thus $Phi(h')=[h']=[h]$.



Noting that $TH$ is closed subspace in the question, $H/THcong (TH)^perp$.






share|cite|improve this answer











$endgroup$









  • 1




    $begingroup$
    thanks, so hypothesis of $T$ fredholm is needed for asume $T(X)$ is closed
    $endgroup$
    – user89940
    Dec 1 '18 at 3:10










  • $begingroup$
    For any subset $S$ of $H$, $H/overline{span{S}}=S^perp$. The very usage of $T(H)$ is closed is $T(H)=overline{span{T(H)}}$
    $endgroup$
    – C.Ding
    Dec 1 '18 at 4:13












  • $begingroup$
    A better answer has been updated.
    $endgroup$
    – C.Ding
    Dec 1 '18 at 4:23












  • $begingroup$
    the hypothesis of $T(H)$ closed is needed for definition in Hilbert version right? because in Banach version $T$ operator with finite coker have image closed. But in hilbert version say "finite dimension of $Ker(T)$ and $Ker(T^{*})$" not impliy $T(H)$ closed? like this answer math.stackexchange.com/questions/1107449/…
    $endgroup$
    – user89940
    Dec 1 '18 at 16:15








  • 1




    $begingroup$
    Yes. If you define coker of an operator $u:Xto Y$ between Banach spaces as $ker u^#$, you will also need the closedness of $uX$ in the definition of a Fredholm operator. If you define the coker of $u$ as a linear space $Y/uX$, then you need not the closedness of uX in any version.
    $endgroup$
    – C.Ding
    Dec 5 '18 at 7:53














1












1








1





$begingroup$


For any closed subspace $K$ of a Hilbert space $H$, we have
$$H/Kcong K^perp.$$




Proof.



$newcommand{co}{operatorname{coker}}$Let begin{align*}Phi: & K^perpto H/K\
& hmapsto [h]end{align*}



(1) Of course, $Phi$ is linear bounded.



(2) $Phi$ is injective. Suppose $hin K^perp$ such that $Phi(h)=0$, then $hin K^perpcap K$, so $h=0$.



(3) $Phi$ is surjective. For any $hin H$, there is some $h'in K^perp$ such that $h-h'in K$, thus $Phi(h')=[h']=[h]$.



Noting that $TH$ is closed subspace in the question, $H/THcong (TH)^perp$.






share|cite|improve this answer











$endgroup$




For any closed subspace $K$ of a Hilbert space $H$, we have
$$H/Kcong K^perp.$$




Proof.



$newcommand{co}{operatorname{coker}}$Let begin{align*}Phi: & K^perpto H/K\
& hmapsto [h]end{align*}



(1) Of course, $Phi$ is linear bounded.



(2) $Phi$ is injective. Suppose $hin K^perp$ such that $Phi(h)=0$, then $hin K^perpcap K$, so $h=0$.



(3) $Phi$ is surjective. For any $hin H$, there is some $h'in K^perp$ such that $h-h'in K$, thus $Phi(h')=[h']=[h]$.



Noting that $TH$ is closed subspace in the question, $H/THcong (TH)^perp$.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Dec 1 '18 at 4:22

























answered Dec 1 '18 at 2:31









C.DingC.Ding

1,3911321




1,3911321








  • 1




    $begingroup$
    thanks, so hypothesis of $T$ fredholm is needed for asume $T(X)$ is closed
    $endgroup$
    – user89940
    Dec 1 '18 at 3:10










  • $begingroup$
    For any subset $S$ of $H$, $H/overline{span{S}}=S^perp$. The very usage of $T(H)$ is closed is $T(H)=overline{span{T(H)}}$
    $endgroup$
    – C.Ding
    Dec 1 '18 at 4:13












  • $begingroup$
    A better answer has been updated.
    $endgroup$
    – C.Ding
    Dec 1 '18 at 4:23












  • $begingroup$
    the hypothesis of $T(H)$ closed is needed for definition in Hilbert version right? because in Banach version $T$ operator with finite coker have image closed. But in hilbert version say "finite dimension of $Ker(T)$ and $Ker(T^{*})$" not impliy $T(H)$ closed? like this answer math.stackexchange.com/questions/1107449/…
    $endgroup$
    – user89940
    Dec 1 '18 at 16:15








  • 1




    $begingroup$
    Yes. If you define coker of an operator $u:Xto Y$ between Banach spaces as $ker u^#$, you will also need the closedness of $uX$ in the definition of a Fredholm operator. If you define the coker of $u$ as a linear space $Y/uX$, then you need not the closedness of uX in any version.
    $endgroup$
    – C.Ding
    Dec 5 '18 at 7:53














  • 1




    $begingroup$
    thanks, so hypothesis of $T$ fredholm is needed for asume $T(X)$ is closed
    $endgroup$
    – user89940
    Dec 1 '18 at 3:10










  • $begingroup$
    For any subset $S$ of $H$, $H/overline{span{S}}=S^perp$. The very usage of $T(H)$ is closed is $T(H)=overline{span{T(H)}}$
    $endgroup$
    – C.Ding
    Dec 1 '18 at 4:13












  • $begingroup$
    A better answer has been updated.
    $endgroup$
    – C.Ding
    Dec 1 '18 at 4:23












  • $begingroup$
    the hypothesis of $T(H)$ closed is needed for definition in Hilbert version right? because in Banach version $T$ operator with finite coker have image closed. But in hilbert version say "finite dimension of $Ker(T)$ and $Ker(T^{*})$" not impliy $T(H)$ closed? like this answer math.stackexchange.com/questions/1107449/…
    $endgroup$
    – user89940
    Dec 1 '18 at 16:15








  • 1




    $begingroup$
    Yes. If you define coker of an operator $u:Xto Y$ between Banach spaces as $ker u^#$, you will also need the closedness of $uX$ in the definition of a Fredholm operator. If you define the coker of $u$ as a linear space $Y/uX$, then you need not the closedness of uX in any version.
    $endgroup$
    – C.Ding
    Dec 5 '18 at 7:53








1




1




$begingroup$
thanks, so hypothesis of $T$ fredholm is needed for asume $T(X)$ is closed
$endgroup$
– user89940
Dec 1 '18 at 3:10




$begingroup$
thanks, so hypothesis of $T$ fredholm is needed for asume $T(X)$ is closed
$endgroup$
– user89940
Dec 1 '18 at 3:10












$begingroup$
For any subset $S$ of $H$, $H/overline{span{S}}=S^perp$. The very usage of $T(H)$ is closed is $T(H)=overline{span{T(H)}}$
$endgroup$
– C.Ding
Dec 1 '18 at 4:13






$begingroup$
For any subset $S$ of $H$, $H/overline{span{S}}=S^perp$. The very usage of $T(H)$ is closed is $T(H)=overline{span{T(H)}}$
$endgroup$
– C.Ding
Dec 1 '18 at 4:13














$begingroup$
A better answer has been updated.
$endgroup$
– C.Ding
Dec 1 '18 at 4:23






$begingroup$
A better answer has been updated.
$endgroup$
– C.Ding
Dec 1 '18 at 4:23














$begingroup$
the hypothesis of $T(H)$ closed is needed for definition in Hilbert version right? because in Banach version $T$ operator with finite coker have image closed. But in hilbert version say "finite dimension of $Ker(T)$ and $Ker(T^{*})$" not impliy $T(H)$ closed? like this answer math.stackexchange.com/questions/1107449/…
$endgroup$
– user89940
Dec 1 '18 at 16:15






$begingroup$
the hypothesis of $T(H)$ closed is needed for definition in Hilbert version right? because in Banach version $T$ operator with finite coker have image closed. But in hilbert version say "finite dimension of $Ker(T)$ and $Ker(T^{*})$" not impliy $T(H)$ closed? like this answer math.stackexchange.com/questions/1107449/…
$endgroup$
– user89940
Dec 1 '18 at 16:15






1




1




$begingroup$
Yes. If you define coker of an operator $u:Xto Y$ between Banach spaces as $ker u^#$, you will also need the closedness of $uX$ in the definition of a Fredholm operator. If you define the coker of $u$ as a linear space $Y/uX$, then you need not the closedness of uX in any version.
$endgroup$
– C.Ding
Dec 5 '18 at 7:53




$begingroup$
Yes. If you define coker of an operator $u:Xto Y$ between Banach spaces as $ker u^#$, you will also need the closedness of $uX$ in the definition of a Fredholm operator. If you define the coker of $u$ as a linear space $Y/uX$, then you need not the closedness of uX in any version.
$endgroup$
– C.Ding
Dec 5 '18 at 7:53


















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