Connected component of ${(x_1,…,x_n) ; | ; x_1^2+…+{x_{n-1}}^2-x_n^2 neq 0}$
$begingroup$
The question is in the title, actually for $n=2$, it's okay, for $n=3$, I thought that :
${(x_1,...,x_n) ; | ; x_1^2+x_2^2-{x_{3}}^2 < 0 }, {(x_1,...,x_n) ; | ; x_1^2+x_2^2-{x_{3}}^2 > 0 }$ are the connected component.
Actually, for $n geq 4$, I have the impression that ${(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 < 0 }, {(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 > 0 }$ are the connected component, cause each are open and closed, but I need to prove that it's connected.
Anyone could help me, please ?
Thank you !
general-topology analysis connectedness path-connected
$endgroup$
|
show 2 more comments
$begingroup$
The question is in the title, actually for $n=2$, it's okay, for $n=3$, I thought that :
${(x_1,...,x_n) ; | ; x_1^2+x_2^2-{x_{3}}^2 < 0 }, {(x_1,...,x_n) ; | ; x_1^2+x_2^2-{x_{3}}^2 > 0 }$ are the connected component.
Actually, for $n geq 4$, I have the impression that ${(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 < 0 }, {(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 > 0 }$ are the connected component, cause each are open and closed, but I need to prove that it's connected.
Anyone could help me, please ?
Thank you !
general-topology analysis connectedness path-connected
$endgroup$
$begingroup$
"I thought that" - what makes you think so?
$endgroup$
– lisyarus
Jan 16 at 17:08
$begingroup$
The two sets are closed and open. So, for sure there is at least two connex components. And each set seems connected, and even path connected, but I didn't prove it in an explicit way, that's why I've written "I thought".
$endgroup$
– ChocoSavour
Jan 16 at 17:10
$begingroup$
@ChocoSavour ${(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 < 0 }$ is open but not close.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:19
1
$begingroup$
@mathcounterexamples.net I meant closed in ${(x_1,..., x_n) ; | ; x_1^2+x_2^2+...-x_n^2 neq 0 }$, for the topology induced by $mathbb{R}^n$, isn't it ?
$endgroup$
– ChocoSavour
Jan 16 at 17:21
$begingroup$
Then you should precise your question saying that you're looking for the connected components for the induced topology. As stated I understood connected components in $mathbb R^n$.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:25
|
show 2 more comments
$begingroup$
The question is in the title, actually for $n=2$, it's okay, for $n=3$, I thought that :
${(x_1,...,x_n) ; | ; x_1^2+x_2^2-{x_{3}}^2 < 0 }, {(x_1,...,x_n) ; | ; x_1^2+x_2^2-{x_{3}}^2 > 0 }$ are the connected component.
Actually, for $n geq 4$, I have the impression that ${(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 < 0 }, {(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 > 0 }$ are the connected component, cause each are open and closed, but I need to prove that it's connected.
Anyone could help me, please ?
Thank you !
general-topology analysis connectedness path-connected
$endgroup$
The question is in the title, actually for $n=2$, it's okay, for $n=3$, I thought that :
${(x_1,...,x_n) ; | ; x_1^2+x_2^2-{x_{3}}^2 < 0 }, {(x_1,...,x_n) ; | ; x_1^2+x_2^2-{x_{3}}^2 > 0 }$ are the connected component.
Actually, for $n geq 4$, I have the impression that ${(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 < 0 }, {(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 > 0 }$ are the connected component, cause each are open and closed, but I need to prove that it's connected.
Anyone could help me, please ?
Thank you !
general-topology analysis connectedness path-connected
general-topology analysis connectedness path-connected
asked Jan 16 at 17:00
ChocoSavourChocoSavour
34818
34818
$begingroup$
"I thought that" - what makes you think so?
$endgroup$
– lisyarus
Jan 16 at 17:08
$begingroup$
The two sets are closed and open. So, for sure there is at least two connex components. And each set seems connected, and even path connected, but I didn't prove it in an explicit way, that's why I've written "I thought".
$endgroup$
– ChocoSavour
Jan 16 at 17:10
$begingroup$
@ChocoSavour ${(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 < 0 }$ is open but not close.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:19
1
$begingroup$
@mathcounterexamples.net I meant closed in ${(x_1,..., x_n) ; | ; x_1^2+x_2^2+...-x_n^2 neq 0 }$, for the topology induced by $mathbb{R}^n$, isn't it ?
$endgroup$
– ChocoSavour
Jan 16 at 17:21
$begingroup$
Then you should precise your question saying that you're looking for the connected components for the induced topology. As stated I understood connected components in $mathbb R^n$.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:25
|
show 2 more comments
$begingroup$
"I thought that" - what makes you think so?
$endgroup$
– lisyarus
Jan 16 at 17:08
$begingroup$
The two sets are closed and open. So, for sure there is at least two connex components. And each set seems connected, and even path connected, but I didn't prove it in an explicit way, that's why I've written "I thought".
$endgroup$
– ChocoSavour
Jan 16 at 17:10
$begingroup$
@ChocoSavour ${(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 < 0 }$ is open but not close.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:19
1
$begingroup$
@mathcounterexamples.net I meant closed in ${(x_1,..., x_n) ; | ; x_1^2+x_2^2+...-x_n^2 neq 0 }$, for the topology induced by $mathbb{R}^n$, isn't it ?
$endgroup$
– ChocoSavour
Jan 16 at 17:21
$begingroup$
Then you should precise your question saying that you're looking for the connected components for the induced topology. As stated I understood connected components in $mathbb R^n$.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:25
$begingroup$
"I thought that" - what makes you think so?
$endgroup$
– lisyarus
Jan 16 at 17:08
$begingroup$
"I thought that" - what makes you think so?
$endgroup$
– lisyarus
Jan 16 at 17:08
$begingroup$
The two sets are closed and open. So, for sure there is at least two connex components. And each set seems connected, and even path connected, but I didn't prove it in an explicit way, that's why I've written "I thought".
$endgroup$
– ChocoSavour
Jan 16 at 17:10
$begingroup$
The two sets are closed and open. So, for sure there is at least two connex components. And each set seems connected, and even path connected, but I didn't prove it in an explicit way, that's why I've written "I thought".
$endgroup$
– ChocoSavour
Jan 16 at 17:10
$begingroup$
@ChocoSavour ${(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 < 0 }$ is open but not close.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:19
$begingroup$
@ChocoSavour ${(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 < 0 }$ is open but not close.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:19
1
1
$begingroup$
@mathcounterexamples.net I meant closed in ${(x_1,..., x_n) ; | ; x_1^2+x_2^2+...-x_n^2 neq 0 }$, for the topology induced by $mathbb{R}^n$, isn't it ?
$endgroup$
– ChocoSavour
Jan 16 at 17:21
$begingroup$
@mathcounterexamples.net I meant closed in ${(x_1,..., x_n) ; | ; x_1^2+x_2^2+...-x_n^2 neq 0 }$, for the topology induced by $mathbb{R}^n$, isn't it ?
$endgroup$
– ChocoSavour
Jan 16 at 17:21
$begingroup$
Then you should precise your question saying that you're looking for the connected components for the induced topology. As stated I understood connected components in $mathbb R^n$.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:25
$begingroup$
Then you should precise your question saying that you're looking for the connected components for the induced topology. As stated I understood connected components in $mathbb R^n$.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:25
|
show 2 more comments
1 Answer
1
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$begingroup$
Let’s note $S_n= {(x_1,...,x_n) in mathbb R^n ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 neq 0}$
Case $n=2$
$S_2={(x,y) in mathbb R^2 mid x^2 neq y^2} ={(x,y) in mathbb R^2 mid x neq y wedge x neq -y}$ has 4 connected components.
Case $n ge 3$
Let’s prove that in that case, $S_n$ has 3 connected components, namely:
$$begin{aligned}
S_n^+ &= left{(x_1,...,x_n) in mathbb R^n mid sqrt{x_1^2+...+{x_{n-1}}^2}< x_nright}\
S_n^0 &= left{(x_1,...,x_n) in mathbb R^n mid -sqrt{x_1^2+...+{x_{n-1}}^2}< x_n < sqrt{x_1^2+...+{x_{n-1}}^2}right}\
S_n^- &= left{(x_1,...,x_n) in mathbb R^n mid x_n < -sqrt{x_1^2+...+{x_{n-1}}^2}right}
end{aligned}$$
Those 3 opens are in fact path connected. $S_n^+$ and $S_n^-$ are convex. Following question: when is the epigraph a convex cone? is a good basis for the proof.
$S_n^0$ is path connected and therefore connected. Use « vertical » lines going to the hyperplane $x_n=0$ and one or two segment lines in the hyperplane $x_n=0$, to avoid passing through the origin.
$endgroup$
$begingroup$
Thank you very much !
$endgroup$
– ChocoSavour
Jan 22 at 16:31
add a comment |
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1 Answer
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1 Answer
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$begingroup$
Let’s note $S_n= {(x_1,...,x_n) in mathbb R^n ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 neq 0}$
Case $n=2$
$S_2={(x,y) in mathbb R^2 mid x^2 neq y^2} ={(x,y) in mathbb R^2 mid x neq y wedge x neq -y}$ has 4 connected components.
Case $n ge 3$
Let’s prove that in that case, $S_n$ has 3 connected components, namely:
$$begin{aligned}
S_n^+ &= left{(x_1,...,x_n) in mathbb R^n mid sqrt{x_1^2+...+{x_{n-1}}^2}< x_nright}\
S_n^0 &= left{(x_1,...,x_n) in mathbb R^n mid -sqrt{x_1^2+...+{x_{n-1}}^2}< x_n < sqrt{x_1^2+...+{x_{n-1}}^2}right}\
S_n^- &= left{(x_1,...,x_n) in mathbb R^n mid x_n < -sqrt{x_1^2+...+{x_{n-1}}^2}right}
end{aligned}$$
Those 3 opens are in fact path connected. $S_n^+$ and $S_n^-$ are convex. Following question: when is the epigraph a convex cone? is a good basis for the proof.
$S_n^0$ is path connected and therefore connected. Use « vertical » lines going to the hyperplane $x_n=0$ and one or two segment lines in the hyperplane $x_n=0$, to avoid passing through the origin.
$endgroup$
$begingroup$
Thank you very much !
$endgroup$
– ChocoSavour
Jan 22 at 16:31
add a comment |
$begingroup$
Let’s note $S_n= {(x_1,...,x_n) in mathbb R^n ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 neq 0}$
Case $n=2$
$S_2={(x,y) in mathbb R^2 mid x^2 neq y^2} ={(x,y) in mathbb R^2 mid x neq y wedge x neq -y}$ has 4 connected components.
Case $n ge 3$
Let’s prove that in that case, $S_n$ has 3 connected components, namely:
$$begin{aligned}
S_n^+ &= left{(x_1,...,x_n) in mathbb R^n mid sqrt{x_1^2+...+{x_{n-1}}^2}< x_nright}\
S_n^0 &= left{(x_1,...,x_n) in mathbb R^n mid -sqrt{x_1^2+...+{x_{n-1}}^2}< x_n < sqrt{x_1^2+...+{x_{n-1}}^2}right}\
S_n^- &= left{(x_1,...,x_n) in mathbb R^n mid x_n < -sqrt{x_1^2+...+{x_{n-1}}^2}right}
end{aligned}$$
Those 3 opens are in fact path connected. $S_n^+$ and $S_n^-$ are convex. Following question: when is the epigraph a convex cone? is a good basis for the proof.
$S_n^0$ is path connected and therefore connected. Use « vertical » lines going to the hyperplane $x_n=0$ and one or two segment lines in the hyperplane $x_n=0$, to avoid passing through the origin.
$endgroup$
$begingroup$
Thank you very much !
$endgroup$
– ChocoSavour
Jan 22 at 16:31
add a comment |
$begingroup$
Let’s note $S_n= {(x_1,...,x_n) in mathbb R^n ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 neq 0}$
Case $n=2$
$S_2={(x,y) in mathbb R^2 mid x^2 neq y^2} ={(x,y) in mathbb R^2 mid x neq y wedge x neq -y}$ has 4 connected components.
Case $n ge 3$
Let’s prove that in that case, $S_n$ has 3 connected components, namely:
$$begin{aligned}
S_n^+ &= left{(x_1,...,x_n) in mathbb R^n mid sqrt{x_1^2+...+{x_{n-1}}^2}< x_nright}\
S_n^0 &= left{(x_1,...,x_n) in mathbb R^n mid -sqrt{x_1^2+...+{x_{n-1}}^2}< x_n < sqrt{x_1^2+...+{x_{n-1}}^2}right}\
S_n^- &= left{(x_1,...,x_n) in mathbb R^n mid x_n < -sqrt{x_1^2+...+{x_{n-1}}^2}right}
end{aligned}$$
Those 3 opens are in fact path connected. $S_n^+$ and $S_n^-$ are convex. Following question: when is the epigraph a convex cone? is a good basis for the proof.
$S_n^0$ is path connected and therefore connected. Use « vertical » lines going to the hyperplane $x_n=0$ and one or two segment lines in the hyperplane $x_n=0$, to avoid passing through the origin.
$endgroup$
Let’s note $S_n= {(x_1,...,x_n) in mathbb R^n ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 neq 0}$
Case $n=2$
$S_2={(x,y) in mathbb R^2 mid x^2 neq y^2} ={(x,y) in mathbb R^2 mid x neq y wedge x neq -y}$ has 4 connected components.
Case $n ge 3$
Let’s prove that in that case, $S_n$ has 3 connected components, namely:
$$begin{aligned}
S_n^+ &= left{(x_1,...,x_n) in mathbb R^n mid sqrt{x_1^2+...+{x_{n-1}}^2}< x_nright}\
S_n^0 &= left{(x_1,...,x_n) in mathbb R^n mid -sqrt{x_1^2+...+{x_{n-1}}^2}< x_n < sqrt{x_1^2+...+{x_{n-1}}^2}right}\
S_n^- &= left{(x_1,...,x_n) in mathbb R^n mid x_n < -sqrt{x_1^2+...+{x_{n-1}}^2}right}
end{aligned}$$
Those 3 opens are in fact path connected. $S_n^+$ and $S_n^-$ are convex. Following question: when is the epigraph a convex cone? is a good basis for the proof.
$S_n^0$ is path connected and therefore connected. Use « vertical » lines going to the hyperplane $x_n=0$ and one or two segment lines in the hyperplane $x_n=0$, to avoid passing through the origin.
edited Jan 17 at 7:05
answered Jan 16 at 20:49
mathcounterexamples.netmathcounterexamples.net
26.9k22158
26.9k22158
$begingroup$
Thank you very much !
$endgroup$
– ChocoSavour
Jan 22 at 16:31
add a comment |
$begingroup$
Thank you very much !
$endgroup$
– ChocoSavour
Jan 22 at 16:31
$begingroup$
Thank you very much !
$endgroup$
– ChocoSavour
Jan 22 at 16:31
$begingroup$
Thank you very much !
$endgroup$
– ChocoSavour
Jan 22 at 16:31
add a comment |
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$begingroup$
"I thought that" - what makes you think so?
$endgroup$
– lisyarus
Jan 16 at 17:08
$begingroup$
The two sets are closed and open. So, for sure there is at least two connex components. And each set seems connected, and even path connected, but I didn't prove it in an explicit way, that's why I've written "I thought".
$endgroup$
– ChocoSavour
Jan 16 at 17:10
$begingroup$
@ChocoSavour ${(x_1,...,x_n) ; | ; x_1^2+...+{x_{n-1}}^2-x_n^2 < 0 }$ is open but not close.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:19
1
$begingroup$
@mathcounterexamples.net I meant closed in ${(x_1,..., x_n) ; | ; x_1^2+x_2^2+...-x_n^2 neq 0 }$, for the topology induced by $mathbb{R}^n$, isn't it ?
$endgroup$
– ChocoSavour
Jan 16 at 17:21
$begingroup$
Then you should precise your question saying that you're looking for the connected components for the induced topology. As stated I understood connected components in $mathbb R^n$.
$endgroup$
– mathcounterexamples.net
Jan 16 at 17:25