Results 1 to 4 of 4

Thread: Left cosets

  1. #1
    MHF Contributor Amer's Avatar
    Joined
    May 2009
    From
    Jordan
    Posts
    1,093

    Left cosets

    find all left coset taking the subgroup generated by <(1,2)>

    the group is \mathbb{Z}_2\times \mathbb{Z}_4

    we have the subgroup h={(0,0),(1,2)}

    \mathbb{Z}_2\times \mathbb{Z}_4 =[(0,0),(0,1),(0,2),(0,3),(1,0),(1,1),(1,2),(1,3)]

    I take all elements not in h and add them to h to get the left coset but I have repeated elements so how I can chose elements such that I do not have repeated ones

    the book said

    h+(0,0) = h

    h+(1,0)

    h+(0,1)

    h+(1,1)

    how the book take these elements can you help
    is there a way to chose these elements
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor Drexel28's Avatar
    Joined
    Nov 2009
    From
    College Park, Maryland
    Posts
    4,542
    Thanks
    11
    Quote Originally Posted by Amer View Post
    find all left coset taking the subgroup generated by <(1,2)>

    the group is \mathbb{Z}_2\times \mathbb{Z}_4

    we have the subgroup h={(0,0),(1,2)}

    \mathbb{Z}_2\times \mathbb{Z}_4 =[(0,0),(0,1),(0,2),(0,3),(1,0),(1,1),(1,2),(1,3)]

    I take all elements not in h and add them to h to get the left coset but I have repeated elements so how I can chose elements such that I do not have repeated ones

    the book said

    h+(0,0) = h

    h+(1,0)

    h+(0,1)

    h+(1,1)

    how the book take these elements can you help
    is there a way to chose these elements
    Do you know Lagrange's theorem? Since \left|\mathbb{Z}_2\oplus \mathbb{Z}_4\right|=8 and \text{ord }\left(1,2\right)=2\implies\left|\left \langle \left(1,2\right)\right \rangle\right|=2 we mus only find \frac{8}{2}=4 subgroups. And, since the subgroup itself is always a coset we must only find three more subgroup. So how about the four cosets \left\langle \left(1,2\right)\right \rangle=H,\left(1,1\right)+H,\left(0,2\right)+H,\l  eft(0,3\right)+H?

    There is no diehard way, that I know to pick the elements. In this case, and some others, you can eye-ball the subgroup to see what will give you distinct cosets.
    Last edited by Drexel28; January 11th 2010 at 09:47 AM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor Amer's Avatar
    Joined
    May 2009
    From
    Jordan
    Posts
    1,093
    Quote Originally Posted by Drexel28 View Post
    Do you know Lagrange's theorem? Since \left|\mathbb{Z}_2\oplus \mathbb{Z}_4\right|=8 and \text{ord }\left(1,2\right)=4\implies\left|\left \langle \left(1,2\right)\right \rangle\right|=2 we mus only find \frac{8}{2}=4 subgroups. And, since the subgroup itself is always a coset we must only find one more subgroup. So how about the four cosets \left\langle \left(1,2\right)\right \rangle=H,\left(1,1\right)+H,\left(0,2\right)+H,\l  eft(0,3\right)+H?

    There is no diehard way, that I know to pick the elements. In this case, and some others, you can eye-ball the subgroup to see what will give you distinct cosets.
    I know it, and I know I have 4 subgroups in the left coset

    it is clear now thank you very much
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor Drexel28's Avatar
    Joined
    Nov 2009
    From
    College Park, Maryland
    Posts
    4,542
    Thanks
    11
    Quote Originally Posted by Amer View Post
    I know it, and I know I have 4 subgroups in the left coset

    it is clear now thank you very much
    I made a typo! I'm sure you paid no mind to it, but I though I should point it out.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Left and Right cosets.
    Posted in the Advanced Algebra Forum
    Replies: 12
    Last Post: February 2nd 2010, 01:35 PM
  2. left and right cosets
    Posted in the Advanced Algebra Forum
    Replies: 10
    Last Post: November 4th 2009, 08:42 PM
  3. Left and Right Cosets
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: April 22nd 2009, 11:06 PM
  4. Cardinality of right and left cosets.
    Posted in the Discrete Math Forum
    Replies: 6
    Last Post: December 23rd 2008, 08:11 AM
  5. right and left cosets
    Posted in the Advanced Algebra Forum
    Replies: 2
    Last Post: December 15th 2008, 06:08 PM

Search Tags


/mathhelpforum @mathhelpforum