Do i imagine the linear (straight line) homotopy in a correct way?












1












$begingroup$


Today i learned about the linear homotopy which says that any two paths $f_0, f_1$ in $mathbb{R}^n$ are homotopic via the homotopy $$ f_t(s) = (1-t)f_0(s) + tf_1(s)$$



Am i right in imagining the given homotopy as something like this?



enter image description here



such that $F(s,t) = f_t(s) $ are simply the linesegments going from $f_0(s)$ towards $f_1(s)$ as the straight lines (which "connect" $f_0$ and $f_1$ for every $sin [0,1]$) as drawn in the picture?



Sorry if this question might be a trivial one, i just want to make sure i don't get things wrong.



Thanks for any kind of feedback!










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$endgroup$








  • 1




    $begingroup$
    It's correct. Furthermore, any point $s$ moves along its straight line at constant speed.
    $endgroup$
    – Lukas Kofler
    1 hour ago










  • $begingroup$
    isn't the point $t$ rather moving along its straight line? to me, $s$ is the parameter moving along the lines from $x_0$ to $x_1$ whereas $t$ moves along the straight linesegments between $f_0$ and $f_1$
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    That's what I was trying to say, sorry -- a fixed point $f_0(s)$ moves at constant speed as $t$ varies.
    $endgroup$
    – Lukas Kofler
    1 hour ago
















1












$begingroup$


Today i learned about the linear homotopy which says that any two paths $f_0, f_1$ in $mathbb{R}^n$ are homotopic via the homotopy $$ f_t(s) = (1-t)f_0(s) + tf_1(s)$$



Am i right in imagining the given homotopy as something like this?



enter image description here



such that $F(s,t) = f_t(s) $ are simply the linesegments going from $f_0(s)$ towards $f_1(s)$ as the straight lines (which "connect" $f_0$ and $f_1$ for every $sin [0,1]$) as drawn in the picture?



Sorry if this question might be a trivial one, i just want to make sure i don't get things wrong.



Thanks for any kind of feedback!










share|cite|improve this question









$endgroup$








  • 1




    $begingroup$
    It's correct. Furthermore, any point $s$ moves along its straight line at constant speed.
    $endgroup$
    – Lukas Kofler
    1 hour ago










  • $begingroup$
    isn't the point $t$ rather moving along its straight line? to me, $s$ is the parameter moving along the lines from $x_0$ to $x_1$ whereas $t$ moves along the straight linesegments between $f_0$ and $f_1$
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    That's what I was trying to say, sorry -- a fixed point $f_0(s)$ moves at constant speed as $t$ varies.
    $endgroup$
    – Lukas Kofler
    1 hour ago














1












1








1





$begingroup$


Today i learned about the linear homotopy which says that any two paths $f_0, f_1$ in $mathbb{R}^n$ are homotopic via the homotopy $$ f_t(s) = (1-t)f_0(s) + tf_1(s)$$



Am i right in imagining the given homotopy as something like this?



enter image description here



such that $F(s,t) = f_t(s) $ are simply the linesegments going from $f_0(s)$ towards $f_1(s)$ as the straight lines (which "connect" $f_0$ and $f_1$ for every $sin [0,1]$) as drawn in the picture?



Sorry if this question might be a trivial one, i just want to make sure i don't get things wrong.



Thanks for any kind of feedback!










share|cite|improve this question









$endgroup$




Today i learned about the linear homotopy which says that any two paths $f_0, f_1$ in $mathbb{R}^n$ are homotopic via the homotopy $$ f_t(s) = (1-t)f_0(s) + tf_1(s)$$



Am i right in imagining the given homotopy as something like this?



enter image description here



such that $F(s,t) = f_t(s) $ are simply the linesegments going from $f_0(s)$ towards $f_1(s)$ as the straight lines (which "connect" $f_0$ and $f_1$ for every $sin [0,1]$) as drawn in the picture?



Sorry if this question might be a trivial one, i just want to make sure i don't get things wrong.



Thanks for any kind of feedback!







algebraic-topology homotopy-theory path-connected






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asked 1 hour ago









ZestZest

301213




301213








  • 1




    $begingroup$
    It's correct. Furthermore, any point $s$ moves along its straight line at constant speed.
    $endgroup$
    – Lukas Kofler
    1 hour ago










  • $begingroup$
    isn't the point $t$ rather moving along its straight line? to me, $s$ is the parameter moving along the lines from $x_0$ to $x_1$ whereas $t$ moves along the straight linesegments between $f_0$ and $f_1$
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    That's what I was trying to say, sorry -- a fixed point $f_0(s)$ moves at constant speed as $t$ varies.
    $endgroup$
    – Lukas Kofler
    1 hour ago














  • 1




    $begingroup$
    It's correct. Furthermore, any point $s$ moves along its straight line at constant speed.
    $endgroup$
    – Lukas Kofler
    1 hour ago










  • $begingroup$
    isn't the point $t$ rather moving along its straight line? to me, $s$ is the parameter moving along the lines from $x_0$ to $x_1$ whereas $t$ moves along the straight linesegments between $f_0$ and $f_1$
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    That's what I was trying to say, sorry -- a fixed point $f_0(s)$ moves at constant speed as $t$ varies.
    $endgroup$
    – Lukas Kofler
    1 hour ago








1




1




$begingroup$
It's correct. Furthermore, any point $s$ moves along its straight line at constant speed.
$endgroup$
– Lukas Kofler
1 hour ago




$begingroup$
It's correct. Furthermore, any point $s$ moves along its straight line at constant speed.
$endgroup$
– Lukas Kofler
1 hour ago












$begingroup$
isn't the point $t$ rather moving along its straight line? to me, $s$ is the parameter moving along the lines from $x_0$ to $x_1$ whereas $t$ moves along the straight linesegments between $f_0$ and $f_1$
$endgroup$
– Zest
1 hour ago




$begingroup$
isn't the point $t$ rather moving along its straight line? to me, $s$ is the parameter moving along the lines from $x_0$ to $x_1$ whereas $t$ moves along the straight linesegments between $f_0$ and $f_1$
$endgroup$
– Zest
1 hour ago




1




1




$begingroup$
That's what I was trying to say, sorry -- a fixed point $f_0(s)$ moves at constant speed as $t$ varies.
$endgroup$
– Lukas Kofler
1 hour ago




$begingroup$
That's what I was trying to say, sorry -- a fixed point $f_0(s)$ moves at constant speed as $t$ varies.
$endgroup$
– Lukas Kofler
1 hour ago










2 Answers
2






active

oldest

votes


















2












$begingroup$

Yes. Perhaps to help you see why this is true, pick an arbitrary $s$ value $bar{s}$ and call $a := f_0(bar{s})$ and $b := f_1(bar{s})$. Examining the homotopy,
$$
H_{bar{s}}(t) := F(bar{s}, t) = a(1-t) + bt
$$



we see that it is the parametric equation of a straight line connecting points $a$ and $b$ in $mathbb{R}^n$. If you draw this line for each $bar{s}$ choice, you get your diagram. Perhaps write a bit of code to construct such a plot?



Furthermore, one may be interested in the "speed" at which $a$ "moves" to $b$. We find it to be a constant,
$$
dfrac{dH_{bar{s}}}{dt} = b - a
$$






share|cite|improve this answer











$endgroup$













  • $begingroup$
    this is very helpful @jnez71. Thanks a lot!
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    No problem! I added a bit more to cover some of the comments about speed
    $endgroup$
    – jnez71
    1 hour ago



















1












$begingroup$

Yes, it is absolutely correct.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    thank you very much @Paul. Just being curious, what does it mean that your answer is "community wiki"?
    $endgroup$
    – Zest
    1 hour ago










  • $begingroup$
    See math.stackexchange.com/help/privileges/edit-community-wiki. A community wiki can be edited by everybody. Frankly, my answer was only a feedback, and I guess you didn't expect more. But of course it doesn't deserve positive reputation.
    $endgroup$
    – Paul Frost
    1 hour ago










  • $begingroup$
    thanks Paul. In fact, your answer was all i was hoping for. Would you mind me accepting @jnez72's answer rather than yours even though both helped me?
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    No problem - it is okay!
    $endgroup$
    – Paul Frost
    1 hour ago










  • $begingroup$
    By the way, in my opinion it is important to make it visible in the question queue that a question has been answered. If you click at "Unanswered" in the upper left corne of this page, you will read something like "248,877 questions with no upvoted or accepted answers ", the number of course growing. If you look at these questions, you will see that a great many are actually answered in comments. If that should happen to one of your questions, do not hesitate to write an answer and acknowledge it.
    $endgroup$
    – Paul Frost
    1 hour ago














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2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes









2












$begingroup$

Yes. Perhaps to help you see why this is true, pick an arbitrary $s$ value $bar{s}$ and call $a := f_0(bar{s})$ and $b := f_1(bar{s})$. Examining the homotopy,
$$
H_{bar{s}}(t) := F(bar{s}, t) = a(1-t) + bt
$$



we see that it is the parametric equation of a straight line connecting points $a$ and $b$ in $mathbb{R}^n$. If you draw this line for each $bar{s}$ choice, you get your diagram. Perhaps write a bit of code to construct such a plot?



Furthermore, one may be interested in the "speed" at which $a$ "moves" to $b$. We find it to be a constant,
$$
dfrac{dH_{bar{s}}}{dt} = b - a
$$






share|cite|improve this answer











$endgroup$













  • $begingroup$
    this is very helpful @jnez71. Thanks a lot!
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    No problem! I added a bit more to cover some of the comments about speed
    $endgroup$
    – jnez71
    1 hour ago
















2












$begingroup$

Yes. Perhaps to help you see why this is true, pick an arbitrary $s$ value $bar{s}$ and call $a := f_0(bar{s})$ and $b := f_1(bar{s})$. Examining the homotopy,
$$
H_{bar{s}}(t) := F(bar{s}, t) = a(1-t) + bt
$$



we see that it is the parametric equation of a straight line connecting points $a$ and $b$ in $mathbb{R}^n$. If you draw this line for each $bar{s}$ choice, you get your diagram. Perhaps write a bit of code to construct such a plot?



Furthermore, one may be interested in the "speed" at which $a$ "moves" to $b$. We find it to be a constant,
$$
dfrac{dH_{bar{s}}}{dt} = b - a
$$






share|cite|improve this answer











$endgroup$













  • $begingroup$
    this is very helpful @jnez71. Thanks a lot!
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    No problem! I added a bit more to cover some of the comments about speed
    $endgroup$
    – jnez71
    1 hour ago














2












2








2





$begingroup$

Yes. Perhaps to help you see why this is true, pick an arbitrary $s$ value $bar{s}$ and call $a := f_0(bar{s})$ and $b := f_1(bar{s})$. Examining the homotopy,
$$
H_{bar{s}}(t) := F(bar{s}, t) = a(1-t) + bt
$$



we see that it is the parametric equation of a straight line connecting points $a$ and $b$ in $mathbb{R}^n$. If you draw this line for each $bar{s}$ choice, you get your diagram. Perhaps write a bit of code to construct such a plot?



Furthermore, one may be interested in the "speed" at which $a$ "moves" to $b$. We find it to be a constant,
$$
dfrac{dH_{bar{s}}}{dt} = b - a
$$






share|cite|improve this answer











$endgroup$



Yes. Perhaps to help you see why this is true, pick an arbitrary $s$ value $bar{s}$ and call $a := f_0(bar{s})$ and $b := f_1(bar{s})$. Examining the homotopy,
$$
H_{bar{s}}(t) := F(bar{s}, t) = a(1-t) + bt
$$



we see that it is the parametric equation of a straight line connecting points $a$ and $b$ in $mathbb{R}^n$. If you draw this line for each $bar{s}$ choice, you get your diagram. Perhaps write a bit of code to construct such a plot?



Furthermore, one may be interested in the "speed" at which $a$ "moves" to $b$. We find it to be a constant,
$$
dfrac{dH_{bar{s}}}{dt} = b - a
$$







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited 1 hour ago

























answered 1 hour ago









jnez71jnez71

2,495720




2,495720












  • $begingroup$
    this is very helpful @jnez71. Thanks a lot!
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    No problem! I added a bit more to cover some of the comments about speed
    $endgroup$
    – jnez71
    1 hour ago


















  • $begingroup$
    this is very helpful @jnez71. Thanks a lot!
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    No problem! I added a bit more to cover some of the comments about speed
    $endgroup$
    – jnez71
    1 hour ago
















$begingroup$
this is very helpful @jnez71. Thanks a lot!
$endgroup$
– Zest
1 hour ago




$begingroup$
this is very helpful @jnez71. Thanks a lot!
$endgroup$
– Zest
1 hour ago




1




1




$begingroup$
No problem! I added a bit more to cover some of the comments about speed
$endgroup$
– jnez71
1 hour ago




$begingroup$
No problem! I added a bit more to cover some of the comments about speed
$endgroup$
– jnez71
1 hour ago











1












$begingroup$

Yes, it is absolutely correct.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    thank you very much @Paul. Just being curious, what does it mean that your answer is "community wiki"?
    $endgroup$
    – Zest
    1 hour ago










  • $begingroup$
    See math.stackexchange.com/help/privileges/edit-community-wiki. A community wiki can be edited by everybody. Frankly, my answer was only a feedback, and I guess you didn't expect more. But of course it doesn't deserve positive reputation.
    $endgroup$
    – Paul Frost
    1 hour ago










  • $begingroup$
    thanks Paul. In fact, your answer was all i was hoping for. Would you mind me accepting @jnez72's answer rather than yours even though both helped me?
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    No problem - it is okay!
    $endgroup$
    – Paul Frost
    1 hour ago










  • $begingroup$
    By the way, in my opinion it is important to make it visible in the question queue that a question has been answered. If you click at "Unanswered" in the upper left corne of this page, you will read something like "248,877 questions with no upvoted or accepted answers ", the number of course growing. If you look at these questions, you will see that a great many are actually answered in comments. If that should happen to one of your questions, do not hesitate to write an answer and acknowledge it.
    $endgroup$
    – Paul Frost
    1 hour ago


















1












$begingroup$

Yes, it is absolutely correct.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    thank you very much @Paul. Just being curious, what does it mean that your answer is "community wiki"?
    $endgroup$
    – Zest
    1 hour ago










  • $begingroup$
    See math.stackexchange.com/help/privileges/edit-community-wiki. A community wiki can be edited by everybody. Frankly, my answer was only a feedback, and I guess you didn't expect more. But of course it doesn't deserve positive reputation.
    $endgroup$
    – Paul Frost
    1 hour ago










  • $begingroup$
    thanks Paul. In fact, your answer was all i was hoping for. Would you mind me accepting @jnez72's answer rather than yours even though both helped me?
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    No problem - it is okay!
    $endgroup$
    – Paul Frost
    1 hour ago










  • $begingroup$
    By the way, in my opinion it is important to make it visible in the question queue that a question has been answered. If you click at "Unanswered" in the upper left corne of this page, you will read something like "248,877 questions with no upvoted or accepted answers ", the number of course growing. If you look at these questions, you will see that a great many are actually answered in comments. If that should happen to one of your questions, do not hesitate to write an answer and acknowledge it.
    $endgroup$
    – Paul Frost
    1 hour ago
















1












1








1





$begingroup$

Yes, it is absolutely correct.






share|cite|improve this answer











$endgroup$



Yes, it is absolutely correct.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








answered 1 hour ago


























community wiki





Paul Frost













  • $begingroup$
    thank you very much @Paul. Just being curious, what does it mean that your answer is "community wiki"?
    $endgroup$
    – Zest
    1 hour ago










  • $begingroup$
    See math.stackexchange.com/help/privileges/edit-community-wiki. A community wiki can be edited by everybody. Frankly, my answer was only a feedback, and I guess you didn't expect more. But of course it doesn't deserve positive reputation.
    $endgroup$
    – Paul Frost
    1 hour ago










  • $begingroup$
    thanks Paul. In fact, your answer was all i was hoping for. Would you mind me accepting @jnez72's answer rather than yours even though both helped me?
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    No problem - it is okay!
    $endgroup$
    – Paul Frost
    1 hour ago










  • $begingroup$
    By the way, in my opinion it is important to make it visible in the question queue that a question has been answered. If you click at "Unanswered" in the upper left corne of this page, you will read something like "248,877 questions with no upvoted or accepted answers ", the number of course growing. If you look at these questions, you will see that a great many are actually answered in comments. If that should happen to one of your questions, do not hesitate to write an answer and acknowledge it.
    $endgroup$
    – Paul Frost
    1 hour ago




















  • $begingroup$
    thank you very much @Paul. Just being curious, what does it mean that your answer is "community wiki"?
    $endgroup$
    – Zest
    1 hour ago










  • $begingroup$
    See math.stackexchange.com/help/privileges/edit-community-wiki. A community wiki can be edited by everybody. Frankly, my answer was only a feedback, and I guess you didn't expect more. But of course it doesn't deserve positive reputation.
    $endgroup$
    – Paul Frost
    1 hour ago










  • $begingroup$
    thanks Paul. In fact, your answer was all i was hoping for. Would you mind me accepting @jnez72's answer rather than yours even though both helped me?
    $endgroup$
    – Zest
    1 hour ago






  • 1




    $begingroup$
    No problem - it is okay!
    $endgroup$
    – Paul Frost
    1 hour ago










  • $begingroup$
    By the way, in my opinion it is important to make it visible in the question queue that a question has been answered. If you click at "Unanswered" in the upper left corne of this page, you will read something like "248,877 questions with no upvoted or accepted answers ", the number of course growing. If you look at these questions, you will see that a great many are actually answered in comments. If that should happen to one of your questions, do not hesitate to write an answer and acknowledge it.
    $endgroup$
    – Paul Frost
    1 hour ago


















$begingroup$
thank you very much @Paul. Just being curious, what does it mean that your answer is "community wiki"?
$endgroup$
– Zest
1 hour ago




$begingroup$
thank you very much @Paul. Just being curious, what does it mean that your answer is "community wiki"?
$endgroup$
– Zest
1 hour ago












$begingroup$
See math.stackexchange.com/help/privileges/edit-community-wiki. A community wiki can be edited by everybody. Frankly, my answer was only a feedback, and I guess you didn't expect more. But of course it doesn't deserve positive reputation.
$endgroup$
– Paul Frost
1 hour ago




$begingroup$
See math.stackexchange.com/help/privileges/edit-community-wiki. A community wiki can be edited by everybody. Frankly, my answer was only a feedback, and I guess you didn't expect more. But of course it doesn't deserve positive reputation.
$endgroup$
– Paul Frost
1 hour ago












$begingroup$
thanks Paul. In fact, your answer was all i was hoping for. Would you mind me accepting @jnez72's answer rather than yours even though both helped me?
$endgroup$
– Zest
1 hour ago




$begingroup$
thanks Paul. In fact, your answer was all i was hoping for. Would you mind me accepting @jnez72's answer rather than yours even though both helped me?
$endgroup$
– Zest
1 hour ago




1




1




$begingroup$
No problem - it is okay!
$endgroup$
– Paul Frost
1 hour ago




$begingroup$
No problem - it is okay!
$endgroup$
– Paul Frost
1 hour ago












$begingroup$
By the way, in my opinion it is important to make it visible in the question queue that a question has been answered. If you click at "Unanswered" in the upper left corne of this page, you will read something like "248,877 questions with no upvoted or accepted answers ", the number of course growing. If you look at these questions, you will see that a great many are actually answered in comments. If that should happen to one of your questions, do not hesitate to write an answer and acknowledge it.
$endgroup$
– Paul Frost
1 hour ago






$begingroup$
By the way, in my opinion it is important to make it visible in the question queue that a question has been answered. If you click at "Unanswered" in the upper left corne of this page, you will read something like "248,877 questions with no upvoted or accepted answers ", the number of course growing. If you look at these questions, you will see that a great many are actually answered in comments. If that should happen to one of your questions, do not hesitate to write an answer and acknowledge it.
$endgroup$
– Paul Frost
1 hour ago




















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