Prove that $T$ is the orthonal projection on the range of the right shift
$begingroup$
Consider the following operator on $ell_{mathbb{N}^*}^2(mathbb{C})$ defined as:
$$ T(x_1,x_2,cdots)=(0,x_2,x_3,cdots).$$
I want prove that
$$sigma(T)={0,1}.$$
I have the following idea: let us consider the right shift
$$S_r(x_1,x_2,cdots)=(0,x_1,x_2,x_3,cdots).$$
If I show that $T$ is the orthonal projection on the range of $S_r$, then clearly
$$sigma(T)={0,1}.$$
Because, it is well known that the spectrum of an Orthogonal Projection Operator is equal to ${0,1}$.
Note that
$$T=S_rT_ell,$$
where
$$S_ell(x_1,x_2,cdots)=(x_2,x_3,cdots).$$
functional-analysis operator-theory hilbert-spaces
$endgroup$
add a comment |
$begingroup$
Consider the following operator on $ell_{mathbb{N}^*}^2(mathbb{C})$ defined as:
$$ T(x_1,x_2,cdots)=(0,x_2,x_3,cdots).$$
I want prove that
$$sigma(T)={0,1}.$$
I have the following idea: let us consider the right shift
$$S_r(x_1,x_2,cdots)=(0,x_1,x_2,x_3,cdots).$$
If I show that $T$ is the orthonal projection on the range of $S_r$, then clearly
$$sigma(T)={0,1}.$$
Because, it is well known that the spectrum of an Orthogonal Projection Operator is equal to ${0,1}$.
Note that
$$T=S_rT_ell,$$
where
$$S_ell(x_1,x_2,cdots)=(x_2,x_3,cdots).$$
functional-analysis operator-theory hilbert-spaces
$endgroup$
$begingroup$
I don't understand why all this downvotes? Is the question is obvious?
$endgroup$
– Schüler
Dec 9 '18 at 16:35
add a comment |
$begingroup$
Consider the following operator on $ell_{mathbb{N}^*}^2(mathbb{C})$ defined as:
$$ T(x_1,x_2,cdots)=(0,x_2,x_3,cdots).$$
I want prove that
$$sigma(T)={0,1}.$$
I have the following idea: let us consider the right shift
$$S_r(x_1,x_2,cdots)=(0,x_1,x_2,x_3,cdots).$$
If I show that $T$ is the orthonal projection on the range of $S_r$, then clearly
$$sigma(T)={0,1}.$$
Because, it is well known that the spectrum of an Orthogonal Projection Operator is equal to ${0,1}$.
Note that
$$T=S_rT_ell,$$
where
$$S_ell(x_1,x_2,cdots)=(x_2,x_3,cdots).$$
functional-analysis operator-theory hilbert-spaces
$endgroup$
Consider the following operator on $ell_{mathbb{N}^*}^2(mathbb{C})$ defined as:
$$ T(x_1,x_2,cdots)=(0,x_2,x_3,cdots).$$
I want prove that
$$sigma(T)={0,1}.$$
I have the following idea: let us consider the right shift
$$S_r(x_1,x_2,cdots)=(0,x_1,x_2,x_3,cdots).$$
If I show that $T$ is the orthonal projection on the range of $S_r$, then clearly
$$sigma(T)={0,1}.$$
Because, it is well known that the spectrum of an Orthogonal Projection Operator is equal to ${0,1}$.
Note that
$$T=S_rT_ell,$$
where
$$S_ell(x_1,x_2,cdots)=(x_2,x_3,cdots).$$
functional-analysis operator-theory hilbert-spaces
functional-analysis operator-theory hilbert-spaces
edited Dec 9 '18 at 19:43
Schüler
asked Dec 9 '18 at 13:58
SchülerSchüler
1,4841421
1,4841421
$begingroup$
I don't understand why all this downvotes? Is the question is obvious?
$endgroup$
– Schüler
Dec 9 '18 at 16:35
add a comment |
$begingroup$
I don't understand why all this downvotes? Is the question is obvious?
$endgroup$
– Schüler
Dec 9 '18 at 16:35
$begingroup$
I don't understand why all this downvotes? Is the question is obvious?
$endgroup$
– Schüler
Dec 9 '18 at 16:35
$begingroup$
I don't understand why all this downvotes? Is the question is obvious?
$endgroup$
– Schüler
Dec 9 '18 at 16:35
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
I cannot see why you want to involve the shift at all.
You have $T^2-T=0$, so $${0}={lambda^2-lambda: lambdainsigma(T)}.$$So $sigma(T)={0,1}$.
For a way to prove this without any theory, look at this.
$endgroup$
$begingroup$
Thank you Professor. I don't understant why $T^2-T=0$ implies that $${0}={lambda^2-lambda: lambdainsigma(T)}?$$ My goal to introduce the shift is to show that T is an orthogonal projection.
$endgroup$
– Schüler
Dec 9 '18 at 20:35
$begingroup$
Look up Spectral Mapping Theorem. As for the shift, it is completely irrelevant here. What's your definition of "orthogonal projection"?
$endgroup$
– Martin Argerami
Dec 9 '18 at 20:47
$begingroup$
It is idempotent and self adjoint.
$endgroup$
– Schüler
Dec 9 '18 at 21:00
$begingroup$
So i think we should show that T is self adjoint
$endgroup$
– Schüler
Dec 9 '18 at 21:01
$begingroup$
That was not your question (you asked to prove that the spectrum of $T$ was ${0,1}$). But that $T$ is orthogonal is trivial, by definition: you just calculate $langle Tx,yrangle$ and $langle x,Tyrangle$.
$endgroup$
– Martin Argerami
Dec 9 '18 at 21:13
add a comment |
$begingroup$
First of all, let $e_1 = left( 1, 0, dots right) $ be the first element of the canonical basis for $ell^2(mathbb{C})$ and $W= e_1^{bot}=langle e_irangle_{igeq 2})$ (here $langle bullet rangle$ identifies the linear span).
Both $langle e_1rangle$ and $W$ are $T$-invariant, so $T-lambda Id$ is invertible iff $T-lambda Id |_{langle e_1 rangle} $ and $T-lambda Id|_W$ are both invertible.
$T-lambda Id |_{langle e_1 rangle} equiv -lambda Id $ so it is invertible iff $lambda neq 0$.
$T-lambda Id|_W equiv left(1-lambdaright)Id $ so it is invertible iff $lambda neq 1$.
$endgroup$
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
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oldest
votes
$begingroup$
I cannot see why you want to involve the shift at all.
You have $T^2-T=0$, so $${0}={lambda^2-lambda: lambdainsigma(T)}.$$So $sigma(T)={0,1}$.
For a way to prove this without any theory, look at this.
$endgroup$
$begingroup$
Thank you Professor. I don't understant why $T^2-T=0$ implies that $${0}={lambda^2-lambda: lambdainsigma(T)}?$$ My goal to introduce the shift is to show that T is an orthogonal projection.
$endgroup$
– Schüler
Dec 9 '18 at 20:35
$begingroup$
Look up Spectral Mapping Theorem. As for the shift, it is completely irrelevant here. What's your definition of "orthogonal projection"?
$endgroup$
– Martin Argerami
Dec 9 '18 at 20:47
$begingroup$
It is idempotent and self adjoint.
$endgroup$
– Schüler
Dec 9 '18 at 21:00
$begingroup$
So i think we should show that T is self adjoint
$endgroup$
– Schüler
Dec 9 '18 at 21:01
$begingroup$
That was not your question (you asked to prove that the spectrum of $T$ was ${0,1}$). But that $T$ is orthogonal is trivial, by definition: you just calculate $langle Tx,yrangle$ and $langle x,Tyrangle$.
$endgroup$
– Martin Argerami
Dec 9 '18 at 21:13
add a comment |
$begingroup$
I cannot see why you want to involve the shift at all.
You have $T^2-T=0$, so $${0}={lambda^2-lambda: lambdainsigma(T)}.$$So $sigma(T)={0,1}$.
For a way to prove this without any theory, look at this.
$endgroup$
$begingroup$
Thank you Professor. I don't understant why $T^2-T=0$ implies that $${0}={lambda^2-lambda: lambdainsigma(T)}?$$ My goal to introduce the shift is to show that T is an orthogonal projection.
$endgroup$
– Schüler
Dec 9 '18 at 20:35
$begingroup$
Look up Spectral Mapping Theorem. As for the shift, it is completely irrelevant here. What's your definition of "orthogonal projection"?
$endgroup$
– Martin Argerami
Dec 9 '18 at 20:47
$begingroup$
It is idempotent and self adjoint.
$endgroup$
– Schüler
Dec 9 '18 at 21:00
$begingroup$
So i think we should show that T is self adjoint
$endgroup$
– Schüler
Dec 9 '18 at 21:01
$begingroup$
That was not your question (you asked to prove that the spectrum of $T$ was ${0,1}$). But that $T$ is orthogonal is trivial, by definition: you just calculate $langle Tx,yrangle$ and $langle x,Tyrangle$.
$endgroup$
– Martin Argerami
Dec 9 '18 at 21:13
add a comment |
$begingroup$
I cannot see why you want to involve the shift at all.
You have $T^2-T=0$, so $${0}={lambda^2-lambda: lambdainsigma(T)}.$$So $sigma(T)={0,1}$.
For a way to prove this without any theory, look at this.
$endgroup$
I cannot see why you want to involve the shift at all.
You have $T^2-T=0$, so $${0}={lambda^2-lambda: lambdainsigma(T)}.$$So $sigma(T)={0,1}$.
For a way to prove this without any theory, look at this.
edited Dec 10 '18 at 3:11
answered Dec 9 '18 at 20:21
Martin ArgeramiMartin Argerami
126k1182180
126k1182180
$begingroup$
Thank you Professor. I don't understant why $T^2-T=0$ implies that $${0}={lambda^2-lambda: lambdainsigma(T)}?$$ My goal to introduce the shift is to show that T is an orthogonal projection.
$endgroup$
– Schüler
Dec 9 '18 at 20:35
$begingroup$
Look up Spectral Mapping Theorem. As for the shift, it is completely irrelevant here. What's your definition of "orthogonal projection"?
$endgroup$
– Martin Argerami
Dec 9 '18 at 20:47
$begingroup$
It is idempotent and self adjoint.
$endgroup$
– Schüler
Dec 9 '18 at 21:00
$begingroup$
So i think we should show that T is self adjoint
$endgroup$
– Schüler
Dec 9 '18 at 21:01
$begingroup$
That was not your question (you asked to prove that the spectrum of $T$ was ${0,1}$). But that $T$ is orthogonal is trivial, by definition: you just calculate $langle Tx,yrangle$ and $langle x,Tyrangle$.
$endgroup$
– Martin Argerami
Dec 9 '18 at 21:13
add a comment |
$begingroup$
Thank you Professor. I don't understant why $T^2-T=0$ implies that $${0}={lambda^2-lambda: lambdainsigma(T)}?$$ My goal to introduce the shift is to show that T is an orthogonal projection.
$endgroup$
– Schüler
Dec 9 '18 at 20:35
$begingroup$
Look up Spectral Mapping Theorem. As for the shift, it is completely irrelevant here. What's your definition of "orthogonal projection"?
$endgroup$
– Martin Argerami
Dec 9 '18 at 20:47
$begingroup$
It is idempotent and self adjoint.
$endgroup$
– Schüler
Dec 9 '18 at 21:00
$begingroup$
So i think we should show that T is self adjoint
$endgroup$
– Schüler
Dec 9 '18 at 21:01
$begingroup$
That was not your question (you asked to prove that the spectrum of $T$ was ${0,1}$). But that $T$ is orthogonal is trivial, by definition: you just calculate $langle Tx,yrangle$ and $langle x,Tyrangle$.
$endgroup$
– Martin Argerami
Dec 9 '18 at 21:13
$begingroup$
Thank you Professor. I don't understant why $T^2-T=0$ implies that $${0}={lambda^2-lambda: lambdainsigma(T)}?$$ My goal to introduce the shift is to show that T is an orthogonal projection.
$endgroup$
– Schüler
Dec 9 '18 at 20:35
$begingroup$
Thank you Professor. I don't understant why $T^2-T=0$ implies that $${0}={lambda^2-lambda: lambdainsigma(T)}?$$ My goal to introduce the shift is to show that T is an orthogonal projection.
$endgroup$
– Schüler
Dec 9 '18 at 20:35
$begingroup$
Look up Spectral Mapping Theorem. As for the shift, it is completely irrelevant here. What's your definition of "orthogonal projection"?
$endgroup$
– Martin Argerami
Dec 9 '18 at 20:47
$begingroup$
Look up Spectral Mapping Theorem. As for the shift, it is completely irrelevant here. What's your definition of "orthogonal projection"?
$endgroup$
– Martin Argerami
Dec 9 '18 at 20:47
$begingroup$
It is idempotent and self adjoint.
$endgroup$
– Schüler
Dec 9 '18 at 21:00
$begingroup$
It is idempotent and self adjoint.
$endgroup$
– Schüler
Dec 9 '18 at 21:00
$begingroup$
So i think we should show that T is self adjoint
$endgroup$
– Schüler
Dec 9 '18 at 21:01
$begingroup$
So i think we should show that T is self adjoint
$endgroup$
– Schüler
Dec 9 '18 at 21:01
$begingroup$
That was not your question (you asked to prove that the spectrum of $T$ was ${0,1}$). But that $T$ is orthogonal is trivial, by definition: you just calculate $langle Tx,yrangle$ and $langle x,Tyrangle$.
$endgroup$
– Martin Argerami
Dec 9 '18 at 21:13
$begingroup$
That was not your question (you asked to prove that the spectrum of $T$ was ${0,1}$). But that $T$ is orthogonal is trivial, by definition: you just calculate $langle Tx,yrangle$ and $langle x,Tyrangle$.
$endgroup$
– Martin Argerami
Dec 9 '18 at 21:13
add a comment |
$begingroup$
First of all, let $e_1 = left( 1, 0, dots right) $ be the first element of the canonical basis for $ell^2(mathbb{C})$ and $W= e_1^{bot}=langle e_irangle_{igeq 2})$ (here $langle bullet rangle$ identifies the linear span).
Both $langle e_1rangle$ and $W$ are $T$-invariant, so $T-lambda Id$ is invertible iff $T-lambda Id |_{langle e_1 rangle} $ and $T-lambda Id|_W$ are both invertible.
$T-lambda Id |_{langle e_1 rangle} equiv -lambda Id $ so it is invertible iff $lambda neq 0$.
$T-lambda Id|_W equiv left(1-lambdaright)Id $ so it is invertible iff $lambda neq 1$.
$endgroup$
add a comment |
$begingroup$
First of all, let $e_1 = left( 1, 0, dots right) $ be the first element of the canonical basis for $ell^2(mathbb{C})$ and $W= e_1^{bot}=langle e_irangle_{igeq 2})$ (here $langle bullet rangle$ identifies the linear span).
Both $langle e_1rangle$ and $W$ are $T$-invariant, so $T-lambda Id$ is invertible iff $T-lambda Id |_{langle e_1 rangle} $ and $T-lambda Id|_W$ are both invertible.
$T-lambda Id |_{langle e_1 rangle} equiv -lambda Id $ so it is invertible iff $lambda neq 0$.
$T-lambda Id|_W equiv left(1-lambdaright)Id $ so it is invertible iff $lambda neq 1$.
$endgroup$
add a comment |
$begingroup$
First of all, let $e_1 = left( 1, 0, dots right) $ be the first element of the canonical basis for $ell^2(mathbb{C})$ and $W= e_1^{bot}=langle e_irangle_{igeq 2})$ (here $langle bullet rangle$ identifies the linear span).
Both $langle e_1rangle$ and $W$ are $T$-invariant, so $T-lambda Id$ is invertible iff $T-lambda Id |_{langle e_1 rangle} $ and $T-lambda Id|_W$ are both invertible.
$T-lambda Id |_{langle e_1 rangle} equiv -lambda Id $ so it is invertible iff $lambda neq 0$.
$T-lambda Id|_W equiv left(1-lambdaright)Id $ so it is invertible iff $lambda neq 1$.
$endgroup$
First of all, let $e_1 = left( 1, 0, dots right) $ be the first element of the canonical basis for $ell^2(mathbb{C})$ and $W= e_1^{bot}=langle e_irangle_{igeq 2})$ (here $langle bullet rangle$ identifies the linear span).
Both $langle e_1rangle$ and $W$ are $T$-invariant, so $T-lambda Id$ is invertible iff $T-lambda Id |_{langle e_1 rangle} $ and $T-lambda Id|_W$ are both invertible.
$T-lambda Id |_{langle e_1 rangle} equiv -lambda Id $ so it is invertible iff $lambda neq 0$.
$T-lambda Id|_W equiv left(1-lambdaright)Id $ so it is invertible iff $lambda neq 1$.
answered Dec 9 '18 at 14:21
Lord_BanquoLord_Banquo
417
417
add a comment |
add a comment |
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$begingroup$
I don't understand why all this downvotes? Is the question is obvious?
$endgroup$
– Schüler
Dec 9 '18 at 16:35