Prove that $operatorname{SL}(n,R)$ is connected.












12












$begingroup$


Prove that $operatorname{SL}(n, R)$ is connected.



The problem is I know only topological groups from Munkres only. Again Just started fundamental groups. So if anyone can explain to me how it is true in a lucid language and in an easy way such that it remains in my boundary of knowledge then it would be a great help. I have mentioned what I know.
Again if tag this in the wrong field. Please forgive me.










share|cite|improve this question











$endgroup$








  • 2




    $begingroup$
    Since you asked, my opinion is that you don't need the algebraic topology tag.
    $endgroup$
    – Matt Samuel
    Nov 7 '14 at 16:40










  • $begingroup$
    On the other hand a linear-algebra tag would be very appropriate since, as the answer of @mookid shows, this is a consequence of basic facts in basic linear algebra.
    $endgroup$
    – Lee Mosher
    Nov 7 '14 at 20:56
















12












$begingroup$


Prove that $operatorname{SL}(n, R)$ is connected.



The problem is I know only topological groups from Munkres only. Again Just started fundamental groups. So if anyone can explain to me how it is true in a lucid language and in an easy way such that it remains in my boundary of knowledge then it would be a great help. I have mentioned what I know.
Again if tag this in the wrong field. Please forgive me.










share|cite|improve this question











$endgroup$








  • 2




    $begingroup$
    Since you asked, my opinion is that you don't need the algebraic topology tag.
    $endgroup$
    – Matt Samuel
    Nov 7 '14 at 16:40










  • $begingroup$
    On the other hand a linear-algebra tag would be very appropriate since, as the answer of @mookid shows, this is a consequence of basic facts in basic linear algebra.
    $endgroup$
    – Lee Mosher
    Nov 7 '14 at 20:56














12












12








12


5



$begingroup$


Prove that $operatorname{SL}(n, R)$ is connected.



The problem is I know only topological groups from Munkres only. Again Just started fundamental groups. So if anyone can explain to me how it is true in a lucid language and in an easy way such that it remains in my boundary of knowledge then it would be a great help. I have mentioned what I know.
Again if tag this in the wrong field. Please forgive me.










share|cite|improve this question











$endgroup$




Prove that $operatorname{SL}(n, R)$ is connected.



The problem is I know only topological groups from Munkres only. Again Just started fundamental groups. So if anyone can explain to me how it is true in a lucid language and in an easy way such that it remains in my boundary of knowledge then it would be a great help. I have mentioned what I know.
Again if tag this in the wrong field. Please forgive me.







linear-algebra general-topology topological-groups






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Jan 23 at 13:31









user549397

1,5081418




1,5081418










asked Nov 7 '14 at 16:38









user152715user152715

1




1








  • 2




    $begingroup$
    Since you asked, my opinion is that you don't need the algebraic topology tag.
    $endgroup$
    – Matt Samuel
    Nov 7 '14 at 16:40










  • $begingroup$
    On the other hand a linear-algebra tag would be very appropriate since, as the answer of @mookid shows, this is a consequence of basic facts in basic linear algebra.
    $endgroup$
    – Lee Mosher
    Nov 7 '14 at 20:56














  • 2




    $begingroup$
    Since you asked, my opinion is that you don't need the algebraic topology tag.
    $endgroup$
    – Matt Samuel
    Nov 7 '14 at 16:40










  • $begingroup$
    On the other hand a linear-algebra tag would be very appropriate since, as the answer of @mookid shows, this is a consequence of basic facts in basic linear algebra.
    $endgroup$
    – Lee Mosher
    Nov 7 '14 at 20:56








2




2




$begingroup$
Since you asked, my opinion is that you don't need the algebraic topology tag.
$endgroup$
– Matt Samuel
Nov 7 '14 at 16:40




$begingroup$
Since you asked, my opinion is that you don't need the algebraic topology tag.
$endgroup$
– Matt Samuel
Nov 7 '14 at 16:40












$begingroup$
On the other hand a linear-algebra tag would be very appropriate since, as the answer of @mookid shows, this is a consequence of basic facts in basic linear algebra.
$endgroup$
– Lee Mosher
Nov 7 '14 at 20:56




$begingroup$
On the other hand a linear-algebra tag would be very appropriate since, as the answer of @mookid shows, this is a consequence of basic facts in basic linear algebra.
$endgroup$
– Lee Mosher
Nov 7 '14 at 20:56










2 Answers
2






active

oldest

votes


















3












$begingroup$

Hint: prove that if two matrices can be transformed one into another using row-echelon transformation, then they are connected.





as we focus on elements of $SL_n$, we only need to prove that transvections $L_i to l_i + aL_j$ connect elements.



let $Ain SL_n$, $B$ is the image of $A$ under the transvection $L_i to L_i + aL_j$.



Then
$$
gamma: [0,1]to SL_n
$$defined by
"$gamma(t)$ is the image of $A$ under the transvection $L_i to L_i + taL_j$
" is continuous, and such as $gamma(0) = A$, $gamma(1) = B$ (also, check that for every $t$, $gamma (t)in SL_n$). Hence $A,B$ are path connected.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    How do I do that? Using topological group definition?
    $endgroup$
    – user152715
    Nov 7 '14 at 16:48






  • 1




    $begingroup$
    the transformations have explicit forms. Use the 'path-connected implies connected' implication.
    $endgroup$
    – mookid
    Nov 7 '14 at 16:49












  • $begingroup$
    can you please write this answer ilaborately then atleast I get an idea for this kind of questions.
    $endgroup$
    – user152715
    Nov 7 '14 at 16:49










  • $begingroup$
    Because I am new to deal with these questions. Thats why I am requesting you. Please it will be a great help.
    $endgroup$
    – user152715
    Nov 7 '14 at 16:52










  • $begingroup$
    @user152715 I wrote the hint part. Now it is your turn to finish the proof. Tell me if you have other issues.
    $endgroup$
    – mookid
    Nov 7 '14 at 16:55



















5












$begingroup$


Exercise 2.M.8(a) (Artin's Algebra, 2nd edition). The group $SL_n(mathbb{R})$ is generated by elementary matrices of the first type (see Exercise 2.4.8). Use this fact to prove that $SL_n(mathbb{R})$ is path-connected.




Let $sim$ be the binary operation corresponding to path-connectivity in $SL_n(mathbb{R})$; by my answer here, $sim$ is an equivalence relation.



In order to show $SL_n(mathbb{R})$ is path-connected, it suffices to show $Asim I_n$ for all $Ain SL_n(mathbb{R})$. But by my answer here, $A$ can be written as a (possibly empty) product of elementary matrices of the first type, so it in fact suffices to prove that$$E_{uv}(a)Msim M$$for all $Min SL_n(mathbb{R})$ and Type 1 elementary matrices $E_{uv}(a)$ ($1le u,,vle n$) of the form$$I_n + [a[(i,,j) = (u,,v)]]_{i,,j,=,1}^n.$$Yet$$Mto E_{uv}(b)M$$simply adds $b$ times row $j$ to row $i$, i.e. takes $r_i$ to $r_i+br_j$. For fixed $u$, $v$, $M$, this map is continuous in $b$ (and preserves the determinant), so the continuous function$$X(t) = E_{uv}(ta)M$$over $[0,1]$ takes$$X(0) = M to X(1) = E_{uv}(a)M$$while remaining inside $SL_n(mathbb{R})$, as desired.






share|cite|improve this answer











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    2 Answers
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    2 Answers
    2






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    active

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    active

    oldest

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    3












    $begingroup$

    Hint: prove that if two matrices can be transformed one into another using row-echelon transformation, then they are connected.





    as we focus on elements of $SL_n$, we only need to prove that transvections $L_i to l_i + aL_j$ connect elements.



    let $Ain SL_n$, $B$ is the image of $A$ under the transvection $L_i to L_i + aL_j$.



    Then
    $$
    gamma: [0,1]to SL_n
    $$defined by
    "$gamma(t)$ is the image of $A$ under the transvection $L_i to L_i + taL_j$
    " is continuous, and such as $gamma(0) = A$, $gamma(1) = B$ (also, check that for every $t$, $gamma (t)in SL_n$). Hence $A,B$ are path connected.






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      How do I do that? Using topological group definition?
      $endgroup$
      – user152715
      Nov 7 '14 at 16:48






    • 1




      $begingroup$
      the transformations have explicit forms. Use the 'path-connected implies connected' implication.
      $endgroup$
      – mookid
      Nov 7 '14 at 16:49












    • $begingroup$
      can you please write this answer ilaborately then atleast I get an idea for this kind of questions.
      $endgroup$
      – user152715
      Nov 7 '14 at 16:49










    • $begingroup$
      Because I am new to deal with these questions. Thats why I am requesting you. Please it will be a great help.
      $endgroup$
      – user152715
      Nov 7 '14 at 16:52










    • $begingroup$
      @user152715 I wrote the hint part. Now it is your turn to finish the proof. Tell me if you have other issues.
      $endgroup$
      – mookid
      Nov 7 '14 at 16:55
















    3












    $begingroup$

    Hint: prove that if two matrices can be transformed one into another using row-echelon transformation, then they are connected.





    as we focus on elements of $SL_n$, we only need to prove that transvections $L_i to l_i + aL_j$ connect elements.



    let $Ain SL_n$, $B$ is the image of $A$ under the transvection $L_i to L_i + aL_j$.



    Then
    $$
    gamma: [0,1]to SL_n
    $$defined by
    "$gamma(t)$ is the image of $A$ under the transvection $L_i to L_i + taL_j$
    " is continuous, and such as $gamma(0) = A$, $gamma(1) = B$ (also, check that for every $t$, $gamma (t)in SL_n$). Hence $A,B$ are path connected.






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      How do I do that? Using topological group definition?
      $endgroup$
      – user152715
      Nov 7 '14 at 16:48






    • 1




      $begingroup$
      the transformations have explicit forms. Use the 'path-connected implies connected' implication.
      $endgroup$
      – mookid
      Nov 7 '14 at 16:49












    • $begingroup$
      can you please write this answer ilaborately then atleast I get an idea for this kind of questions.
      $endgroup$
      – user152715
      Nov 7 '14 at 16:49










    • $begingroup$
      Because I am new to deal with these questions. Thats why I am requesting you. Please it will be a great help.
      $endgroup$
      – user152715
      Nov 7 '14 at 16:52










    • $begingroup$
      @user152715 I wrote the hint part. Now it is your turn to finish the proof. Tell me if you have other issues.
      $endgroup$
      – mookid
      Nov 7 '14 at 16:55














    3












    3








    3





    $begingroup$

    Hint: prove that if two matrices can be transformed one into another using row-echelon transformation, then they are connected.





    as we focus on elements of $SL_n$, we only need to prove that transvections $L_i to l_i + aL_j$ connect elements.



    let $Ain SL_n$, $B$ is the image of $A$ under the transvection $L_i to L_i + aL_j$.



    Then
    $$
    gamma: [0,1]to SL_n
    $$defined by
    "$gamma(t)$ is the image of $A$ under the transvection $L_i to L_i + taL_j$
    " is continuous, and such as $gamma(0) = A$, $gamma(1) = B$ (also, check that for every $t$, $gamma (t)in SL_n$). Hence $A,B$ are path connected.






    share|cite|improve this answer











    $endgroup$



    Hint: prove that if two matrices can be transformed one into another using row-echelon transformation, then they are connected.





    as we focus on elements of $SL_n$, we only need to prove that transvections $L_i to l_i + aL_j$ connect elements.



    let $Ain SL_n$, $B$ is the image of $A$ under the transvection $L_i to L_i + aL_j$.



    Then
    $$
    gamma: [0,1]to SL_n
    $$defined by
    "$gamma(t)$ is the image of $A$ under the transvection $L_i to L_i + taL_j$
    " is continuous, and such as $gamma(0) = A$, $gamma(1) = B$ (also, check that for every $t$, $gamma (t)in SL_n$). Hence $A,B$ are path connected.







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    edited Apr 30 '17 at 3:32









    tommy xu3

    9791621




    9791621










    answered Nov 7 '14 at 16:40









    mookidmookid

    25.6k52547




    25.6k52547












    • $begingroup$
      How do I do that? Using topological group definition?
      $endgroup$
      – user152715
      Nov 7 '14 at 16:48






    • 1




      $begingroup$
      the transformations have explicit forms. Use the 'path-connected implies connected' implication.
      $endgroup$
      – mookid
      Nov 7 '14 at 16:49












    • $begingroup$
      can you please write this answer ilaborately then atleast I get an idea for this kind of questions.
      $endgroup$
      – user152715
      Nov 7 '14 at 16:49










    • $begingroup$
      Because I am new to deal with these questions. Thats why I am requesting you. Please it will be a great help.
      $endgroup$
      – user152715
      Nov 7 '14 at 16:52










    • $begingroup$
      @user152715 I wrote the hint part. Now it is your turn to finish the proof. Tell me if you have other issues.
      $endgroup$
      – mookid
      Nov 7 '14 at 16:55


















    • $begingroup$
      How do I do that? Using topological group definition?
      $endgroup$
      – user152715
      Nov 7 '14 at 16:48






    • 1




      $begingroup$
      the transformations have explicit forms. Use the 'path-connected implies connected' implication.
      $endgroup$
      – mookid
      Nov 7 '14 at 16:49












    • $begingroup$
      can you please write this answer ilaborately then atleast I get an idea for this kind of questions.
      $endgroup$
      – user152715
      Nov 7 '14 at 16:49










    • $begingroup$
      Because I am new to deal with these questions. Thats why I am requesting you. Please it will be a great help.
      $endgroup$
      – user152715
      Nov 7 '14 at 16:52










    • $begingroup$
      @user152715 I wrote the hint part. Now it is your turn to finish the proof. Tell me if you have other issues.
      $endgroup$
      – mookid
      Nov 7 '14 at 16:55
















    $begingroup$
    How do I do that? Using topological group definition?
    $endgroup$
    – user152715
    Nov 7 '14 at 16:48




    $begingroup$
    How do I do that? Using topological group definition?
    $endgroup$
    – user152715
    Nov 7 '14 at 16:48




    1




    1




    $begingroup$
    the transformations have explicit forms. Use the 'path-connected implies connected' implication.
    $endgroup$
    – mookid
    Nov 7 '14 at 16:49






    $begingroup$
    the transformations have explicit forms. Use the 'path-connected implies connected' implication.
    $endgroup$
    – mookid
    Nov 7 '14 at 16:49














    $begingroup$
    can you please write this answer ilaborately then atleast I get an idea for this kind of questions.
    $endgroup$
    – user152715
    Nov 7 '14 at 16:49




    $begingroup$
    can you please write this answer ilaborately then atleast I get an idea for this kind of questions.
    $endgroup$
    – user152715
    Nov 7 '14 at 16:49












    $begingroup$
    Because I am new to deal with these questions. Thats why I am requesting you. Please it will be a great help.
    $endgroup$
    – user152715
    Nov 7 '14 at 16:52




    $begingroup$
    Because I am new to deal with these questions. Thats why I am requesting you. Please it will be a great help.
    $endgroup$
    – user152715
    Nov 7 '14 at 16:52












    $begingroup$
    @user152715 I wrote the hint part. Now it is your turn to finish the proof. Tell me if you have other issues.
    $endgroup$
    – mookid
    Nov 7 '14 at 16:55




    $begingroup$
    @user152715 I wrote the hint part. Now it is your turn to finish the proof. Tell me if you have other issues.
    $endgroup$
    – mookid
    Nov 7 '14 at 16:55











    5












    $begingroup$


    Exercise 2.M.8(a) (Artin's Algebra, 2nd edition). The group $SL_n(mathbb{R})$ is generated by elementary matrices of the first type (see Exercise 2.4.8). Use this fact to prove that $SL_n(mathbb{R})$ is path-connected.




    Let $sim$ be the binary operation corresponding to path-connectivity in $SL_n(mathbb{R})$; by my answer here, $sim$ is an equivalence relation.



    In order to show $SL_n(mathbb{R})$ is path-connected, it suffices to show $Asim I_n$ for all $Ain SL_n(mathbb{R})$. But by my answer here, $A$ can be written as a (possibly empty) product of elementary matrices of the first type, so it in fact suffices to prove that$$E_{uv}(a)Msim M$$for all $Min SL_n(mathbb{R})$ and Type 1 elementary matrices $E_{uv}(a)$ ($1le u,,vle n$) of the form$$I_n + [a[(i,,j) = (u,,v)]]_{i,,j,=,1}^n.$$Yet$$Mto E_{uv}(b)M$$simply adds $b$ times row $j$ to row $i$, i.e. takes $r_i$ to $r_i+br_j$. For fixed $u$, $v$, $M$, this map is continuous in $b$ (and preserves the determinant), so the continuous function$$X(t) = E_{uv}(ta)M$$over $[0,1]$ takes$$X(0) = M to X(1) = E_{uv}(a)M$$while remaining inside $SL_n(mathbb{R})$, as desired.






    share|cite|improve this answer











    $endgroup$


















      5












      $begingroup$


      Exercise 2.M.8(a) (Artin's Algebra, 2nd edition). The group $SL_n(mathbb{R})$ is generated by elementary matrices of the first type (see Exercise 2.4.8). Use this fact to prove that $SL_n(mathbb{R})$ is path-connected.




      Let $sim$ be the binary operation corresponding to path-connectivity in $SL_n(mathbb{R})$; by my answer here, $sim$ is an equivalence relation.



      In order to show $SL_n(mathbb{R})$ is path-connected, it suffices to show $Asim I_n$ for all $Ain SL_n(mathbb{R})$. But by my answer here, $A$ can be written as a (possibly empty) product of elementary matrices of the first type, so it in fact suffices to prove that$$E_{uv}(a)Msim M$$for all $Min SL_n(mathbb{R})$ and Type 1 elementary matrices $E_{uv}(a)$ ($1le u,,vle n$) of the form$$I_n + [a[(i,,j) = (u,,v)]]_{i,,j,=,1}^n.$$Yet$$Mto E_{uv}(b)M$$simply adds $b$ times row $j$ to row $i$, i.e. takes $r_i$ to $r_i+br_j$. For fixed $u$, $v$, $M$, this map is continuous in $b$ (and preserves the determinant), so the continuous function$$X(t) = E_{uv}(ta)M$$over $[0,1]$ takes$$X(0) = M to X(1) = E_{uv}(a)M$$while remaining inside $SL_n(mathbb{R})$, as desired.






      share|cite|improve this answer











      $endgroup$
















        5












        5








        5





        $begingroup$


        Exercise 2.M.8(a) (Artin's Algebra, 2nd edition). The group $SL_n(mathbb{R})$ is generated by elementary matrices of the first type (see Exercise 2.4.8). Use this fact to prove that $SL_n(mathbb{R})$ is path-connected.




        Let $sim$ be the binary operation corresponding to path-connectivity in $SL_n(mathbb{R})$; by my answer here, $sim$ is an equivalence relation.



        In order to show $SL_n(mathbb{R})$ is path-connected, it suffices to show $Asim I_n$ for all $Ain SL_n(mathbb{R})$. But by my answer here, $A$ can be written as a (possibly empty) product of elementary matrices of the first type, so it in fact suffices to prove that$$E_{uv}(a)Msim M$$for all $Min SL_n(mathbb{R})$ and Type 1 elementary matrices $E_{uv}(a)$ ($1le u,,vle n$) of the form$$I_n + [a[(i,,j) = (u,,v)]]_{i,,j,=,1}^n.$$Yet$$Mto E_{uv}(b)M$$simply adds $b$ times row $j$ to row $i$, i.e. takes $r_i$ to $r_i+br_j$. For fixed $u$, $v$, $M$, this map is continuous in $b$ (and preserves the determinant), so the continuous function$$X(t) = E_{uv}(ta)M$$over $[0,1]$ takes$$X(0) = M to X(1) = E_{uv}(a)M$$while remaining inside $SL_n(mathbb{R})$, as desired.






        share|cite|improve this answer











        $endgroup$




        Exercise 2.M.8(a) (Artin's Algebra, 2nd edition). The group $SL_n(mathbb{R})$ is generated by elementary matrices of the first type (see Exercise 2.4.8). Use this fact to prove that $SL_n(mathbb{R})$ is path-connected.




        Let $sim$ be the binary operation corresponding to path-connectivity in $SL_n(mathbb{R})$; by my answer here, $sim$ is an equivalence relation.



        In order to show $SL_n(mathbb{R})$ is path-connected, it suffices to show $Asim I_n$ for all $Ain SL_n(mathbb{R})$. But by my answer here, $A$ can be written as a (possibly empty) product of elementary matrices of the first type, so it in fact suffices to prove that$$E_{uv}(a)Msim M$$for all $Min SL_n(mathbb{R})$ and Type 1 elementary matrices $E_{uv}(a)$ ($1le u,,vle n$) of the form$$I_n + [a[(i,,j) = (u,,v)]]_{i,,j,=,1}^n.$$Yet$$Mto E_{uv}(b)M$$simply adds $b$ times row $j$ to row $i$, i.e. takes $r_i$ to $r_i+br_j$. For fixed $u$, $v$, $M$, this map is continuous in $b$ (and preserves the determinant), so the continuous function$$X(t) = E_{uv}(ta)M$$over $[0,1]$ takes$$X(0) = M to X(1) = E_{uv}(a)M$$while remaining inside $SL_n(mathbb{R})$, as desired.







        share|cite|improve this answer














        share|cite|improve this answer



        share|cite|improve this answer








        edited Apr 13 '17 at 12:19









        Community

        1




        1










        answered Sep 24 '15 at 15:57







        user203482





































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