Show that $T:,c_0to c_0;;$, $xmapsto T(x)=(1,x_1,x_2,cdots),$ is non-expansive
$begingroup$
Let $X$ be a normed linear space and $X=c_0$ (the space of sequences of real numbers which converge to $0$). Define
begin{align} T:,&c_0to c_0 \ &xmapsto T(x)=(1,x_1,x_2,cdots), end{align}
for arbitrary $x=(1,x_1,x_2,cdots)in c_0.$ I want to show that $T$ is non-expansive.
Remark: We have that
$$c_0={bar{x}=(x_1,x_2,cdots) :x_nto 0;text{as};nto infty}.$$
MY TRIAL
Let $x,yin c_0.$ WTS: there exists $0leq kleq 1,$ such that $Vert T(x)-T(y) Vert leq k Vert x-y Vert . $
Now,
begin{align} Vert T(x)-T(y) Vert &=Vert (1,x_1,x_2,cdots)-(1,y_1,y_2,cdots) Vert\&=Vert ( 0,x_i-y_i)Vert\&= suplimits_{iin Bbb{N}} {0,|x_i-y_i|}\&= suplimits_{iin Bbb{N}} {|x_i-y_i|}\&=Vert x-y Vert end{align}
Taking $k=1,$ (based on mathworker21's advice and BigbearZzz's help), then
begin{align} Vert T(x)-T(y) Vert leq k Vert x-y Vert . end{align}
I'll be interested to see if you have a different kind of proof.
functional-analysis analysis normed-spaces
$endgroup$
add a comment |
$begingroup$
Let $X$ be a normed linear space and $X=c_0$ (the space of sequences of real numbers which converge to $0$). Define
begin{align} T:,&c_0to c_0 \ &xmapsto T(x)=(1,x_1,x_2,cdots), end{align}
for arbitrary $x=(1,x_1,x_2,cdots)in c_0.$ I want to show that $T$ is non-expansive.
Remark: We have that
$$c_0={bar{x}=(x_1,x_2,cdots) :x_nto 0;text{as};nto infty}.$$
MY TRIAL
Let $x,yin c_0.$ WTS: there exists $0leq kleq 1,$ such that $Vert T(x)-T(y) Vert leq k Vert x-y Vert . $
Now,
begin{align} Vert T(x)-T(y) Vert &=Vert (1,x_1,x_2,cdots)-(1,y_1,y_2,cdots) Vert\&=Vert ( 0,x_i-y_i)Vert\&= suplimits_{iin Bbb{N}} {0,|x_i-y_i|}\&= suplimits_{iin Bbb{N}} {|x_i-y_i|}\&=Vert x-y Vert end{align}
Taking $k=1,$ (based on mathworker21's advice and BigbearZzz's help), then
begin{align} Vert T(x)-T(y) Vert leq k Vert x-y Vert . end{align}
I'll be interested to see if you have a different kind of proof.
functional-analysis analysis normed-spaces
$endgroup$
1
$begingroup$
in your 'WTS', it's equivalent to take $k=1$. also do you know what the norm $||cdot||$ is here? this problem is pretty trivial
$endgroup$
– mathworker21
Dec 14 '18 at 8:16
1
$begingroup$
Yes, your proof is correct.
$endgroup$
– Kavi Rama Murthy
Dec 14 '18 at 8:21
$begingroup$
@Kavi Rama Murthy: Thank you very much Sir.
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:24
add a comment |
$begingroup$
Let $X$ be a normed linear space and $X=c_0$ (the space of sequences of real numbers which converge to $0$). Define
begin{align} T:,&c_0to c_0 \ &xmapsto T(x)=(1,x_1,x_2,cdots), end{align}
for arbitrary $x=(1,x_1,x_2,cdots)in c_0.$ I want to show that $T$ is non-expansive.
Remark: We have that
$$c_0={bar{x}=(x_1,x_2,cdots) :x_nto 0;text{as};nto infty}.$$
MY TRIAL
Let $x,yin c_0.$ WTS: there exists $0leq kleq 1,$ such that $Vert T(x)-T(y) Vert leq k Vert x-y Vert . $
Now,
begin{align} Vert T(x)-T(y) Vert &=Vert (1,x_1,x_2,cdots)-(1,y_1,y_2,cdots) Vert\&=Vert ( 0,x_i-y_i)Vert\&= suplimits_{iin Bbb{N}} {0,|x_i-y_i|}\&= suplimits_{iin Bbb{N}} {|x_i-y_i|}\&=Vert x-y Vert end{align}
Taking $k=1,$ (based on mathworker21's advice and BigbearZzz's help), then
begin{align} Vert T(x)-T(y) Vert leq k Vert x-y Vert . end{align}
I'll be interested to see if you have a different kind of proof.
functional-analysis analysis normed-spaces
$endgroup$
Let $X$ be a normed linear space and $X=c_0$ (the space of sequences of real numbers which converge to $0$). Define
begin{align} T:,&c_0to c_0 \ &xmapsto T(x)=(1,x_1,x_2,cdots), end{align}
for arbitrary $x=(1,x_1,x_2,cdots)in c_0.$ I want to show that $T$ is non-expansive.
Remark: We have that
$$c_0={bar{x}=(x_1,x_2,cdots) :x_nto 0;text{as};nto infty}.$$
MY TRIAL
Let $x,yin c_0.$ WTS: there exists $0leq kleq 1,$ such that $Vert T(x)-T(y) Vert leq k Vert x-y Vert . $
Now,
begin{align} Vert T(x)-T(y) Vert &=Vert (1,x_1,x_2,cdots)-(1,y_1,y_2,cdots) Vert\&=Vert ( 0,x_i-y_i)Vert\&= suplimits_{iin Bbb{N}} {0,|x_i-y_i|}\&= suplimits_{iin Bbb{N}} {|x_i-y_i|}\&=Vert x-y Vert end{align}
Taking $k=1,$ (based on mathworker21's advice and BigbearZzz's help), then
begin{align} Vert T(x)-T(y) Vert leq k Vert x-y Vert . end{align}
I'll be interested to see if you have a different kind of proof.
functional-analysis analysis normed-spaces
functional-analysis analysis normed-spaces
edited Dec 14 '18 at 8:51
Omojola Micheal
asked Dec 14 '18 at 8:12
Omojola MichealOmojola Micheal
1,920324
1,920324
1
$begingroup$
in your 'WTS', it's equivalent to take $k=1$. also do you know what the norm $||cdot||$ is here? this problem is pretty trivial
$endgroup$
– mathworker21
Dec 14 '18 at 8:16
1
$begingroup$
Yes, your proof is correct.
$endgroup$
– Kavi Rama Murthy
Dec 14 '18 at 8:21
$begingroup$
@Kavi Rama Murthy: Thank you very much Sir.
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:24
add a comment |
1
$begingroup$
in your 'WTS', it's equivalent to take $k=1$. also do you know what the norm $||cdot||$ is here? this problem is pretty trivial
$endgroup$
– mathworker21
Dec 14 '18 at 8:16
1
$begingroup$
Yes, your proof is correct.
$endgroup$
– Kavi Rama Murthy
Dec 14 '18 at 8:21
$begingroup$
@Kavi Rama Murthy: Thank you very much Sir.
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:24
1
1
$begingroup$
in your 'WTS', it's equivalent to take $k=1$. also do you know what the norm $||cdot||$ is here? this problem is pretty trivial
$endgroup$
– mathworker21
Dec 14 '18 at 8:16
$begingroup$
in your 'WTS', it's equivalent to take $k=1$. also do you know what the norm $||cdot||$ is here? this problem is pretty trivial
$endgroup$
– mathworker21
Dec 14 '18 at 8:16
1
1
$begingroup$
Yes, your proof is correct.
$endgroup$
– Kavi Rama Murthy
Dec 14 '18 at 8:21
$begingroup$
Yes, your proof is correct.
$endgroup$
– Kavi Rama Murthy
Dec 14 '18 at 8:21
$begingroup$
@Kavi Rama Murthy: Thank you very much Sir.
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:24
$begingroup$
@Kavi Rama Murthy: Thank you very much Sir.
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:24
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
You've computed that
$$begin{align}
||Tx-Ty|| &= sup {0,|x_1-y_1|,|x_2-y_2|,dots},
end{align}$$
whereas we know that
$$
||x-y|| = sup {|x_1-y_1|,|x_2-y_2|,dots}.
$$
All you need to know to solve the problem is that norm for $c_0$ is the supremum norm.
$endgroup$
$begingroup$
Do we need to have $sup?$, seeing that $c_0={bar{x}=(x_1,x_2,cdots) :x_nto 0;text{as};nto infty}.$
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:23
$begingroup$
@Mike It's the standard norm on $c_0$ that makes it a Banach space. I think this should be written in your book/problem sheet.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:24
$begingroup$
The norm on $c_0$ is defined to be $||x|| = sup_{iinBbb N} |x_i|$.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:25
$begingroup$
Maybe I'll get top know that as time goes on! I'm teaching myself Functional analysis with the help of a book. Anyway, is my proof correct?
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:26
$begingroup$
Thanks about the norm info. That is an addition. Thanks!
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:27
|
show 5 more comments
Your Answer
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1 Answer
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1 Answer
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$begingroup$
You've computed that
$$begin{align}
||Tx-Ty|| &= sup {0,|x_1-y_1|,|x_2-y_2|,dots},
end{align}$$
whereas we know that
$$
||x-y|| = sup {|x_1-y_1|,|x_2-y_2|,dots}.
$$
All you need to know to solve the problem is that norm for $c_0$ is the supremum norm.
$endgroup$
$begingroup$
Do we need to have $sup?$, seeing that $c_0={bar{x}=(x_1,x_2,cdots) :x_nto 0;text{as};nto infty}.$
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:23
$begingroup$
@Mike It's the standard norm on $c_0$ that makes it a Banach space. I think this should be written in your book/problem sheet.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:24
$begingroup$
The norm on $c_0$ is defined to be $||x|| = sup_{iinBbb N} |x_i|$.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:25
$begingroup$
Maybe I'll get top know that as time goes on! I'm teaching myself Functional analysis with the help of a book. Anyway, is my proof correct?
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:26
$begingroup$
Thanks about the norm info. That is an addition. Thanks!
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:27
|
show 5 more comments
$begingroup$
You've computed that
$$begin{align}
||Tx-Ty|| &= sup {0,|x_1-y_1|,|x_2-y_2|,dots},
end{align}$$
whereas we know that
$$
||x-y|| = sup {|x_1-y_1|,|x_2-y_2|,dots}.
$$
All you need to know to solve the problem is that norm for $c_0$ is the supremum norm.
$endgroup$
$begingroup$
Do we need to have $sup?$, seeing that $c_0={bar{x}=(x_1,x_2,cdots) :x_nto 0;text{as};nto infty}.$
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:23
$begingroup$
@Mike It's the standard norm on $c_0$ that makes it a Banach space. I think this should be written in your book/problem sheet.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:24
$begingroup$
The norm on $c_0$ is defined to be $||x|| = sup_{iinBbb N} |x_i|$.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:25
$begingroup$
Maybe I'll get top know that as time goes on! I'm teaching myself Functional analysis with the help of a book. Anyway, is my proof correct?
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:26
$begingroup$
Thanks about the norm info. That is an addition. Thanks!
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:27
|
show 5 more comments
$begingroup$
You've computed that
$$begin{align}
||Tx-Ty|| &= sup {0,|x_1-y_1|,|x_2-y_2|,dots},
end{align}$$
whereas we know that
$$
||x-y|| = sup {|x_1-y_1|,|x_2-y_2|,dots}.
$$
All you need to know to solve the problem is that norm for $c_0$ is the supremum norm.
$endgroup$
You've computed that
$$begin{align}
||Tx-Ty|| &= sup {0,|x_1-y_1|,|x_2-y_2|,dots},
end{align}$$
whereas we know that
$$
||x-y|| = sup {|x_1-y_1|,|x_2-y_2|,dots}.
$$
All you need to know to solve the problem is that norm for $c_0$ is the supremum norm.
answered Dec 14 '18 at 8:20
BigbearZzzBigbearZzz
8,88821652
8,88821652
$begingroup$
Do we need to have $sup?$, seeing that $c_0={bar{x}=(x_1,x_2,cdots) :x_nto 0;text{as};nto infty}.$
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:23
$begingroup$
@Mike It's the standard norm on $c_0$ that makes it a Banach space. I think this should be written in your book/problem sheet.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:24
$begingroup$
The norm on $c_0$ is defined to be $||x|| = sup_{iinBbb N} |x_i|$.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:25
$begingroup$
Maybe I'll get top know that as time goes on! I'm teaching myself Functional analysis with the help of a book. Anyway, is my proof correct?
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:26
$begingroup$
Thanks about the norm info. That is an addition. Thanks!
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:27
|
show 5 more comments
$begingroup$
Do we need to have $sup?$, seeing that $c_0={bar{x}=(x_1,x_2,cdots) :x_nto 0;text{as};nto infty}.$
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:23
$begingroup$
@Mike It's the standard norm on $c_0$ that makes it a Banach space. I think this should be written in your book/problem sheet.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:24
$begingroup$
The norm on $c_0$ is defined to be $||x|| = sup_{iinBbb N} |x_i|$.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:25
$begingroup$
Maybe I'll get top know that as time goes on! I'm teaching myself Functional analysis with the help of a book. Anyway, is my proof correct?
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:26
$begingroup$
Thanks about the norm info. That is an addition. Thanks!
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:27
$begingroup$
Do we need to have $sup?$, seeing that $c_0={bar{x}=(x_1,x_2,cdots) :x_nto 0;text{as};nto infty}.$
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:23
$begingroup$
Do we need to have $sup?$, seeing that $c_0={bar{x}=(x_1,x_2,cdots) :x_nto 0;text{as};nto infty}.$
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:23
$begingroup$
@Mike It's the standard norm on $c_0$ that makes it a Banach space. I think this should be written in your book/problem sheet.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:24
$begingroup$
@Mike It's the standard norm on $c_0$ that makes it a Banach space. I think this should be written in your book/problem sheet.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:24
$begingroup$
The norm on $c_0$ is defined to be $||x|| = sup_{iinBbb N} |x_i|$.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:25
$begingroup$
The norm on $c_0$ is defined to be $||x|| = sup_{iinBbb N} |x_i|$.
$endgroup$
– BigbearZzz
Dec 14 '18 at 8:25
$begingroup$
Maybe I'll get top know that as time goes on! I'm teaching myself Functional analysis with the help of a book. Anyway, is my proof correct?
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:26
$begingroup$
Maybe I'll get top know that as time goes on! I'm teaching myself Functional analysis with the help of a book. Anyway, is my proof correct?
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:26
$begingroup$
Thanks about the norm info. That is an addition. Thanks!
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:27
$begingroup$
Thanks about the norm info. That is an addition. Thanks!
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:27
|
show 5 more comments
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1
$begingroup$
in your 'WTS', it's equivalent to take $k=1$. also do you know what the norm $||cdot||$ is here? this problem is pretty trivial
$endgroup$
– mathworker21
Dec 14 '18 at 8:16
1
$begingroup$
Yes, your proof is correct.
$endgroup$
– Kavi Rama Murthy
Dec 14 '18 at 8:21
$begingroup$
@Kavi Rama Murthy: Thank you very much Sir.
$endgroup$
– Omojola Micheal
Dec 14 '18 at 8:24