Invariant factors of a module over a $PID$












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so i need some help. Imagine D is Principal Ideal Domain, and $M$ and $N$ are cyclic modules with order $a$ and $b$ respectevly, and $mdc(a,b)neq 1$. So im asked to prove that the invariant factors of $Mbigoplus N$ are the $gcd(a,b)$ and the $lcm(a,b)$. Im not quite sure how to do this, i know that $M cong D/(a)$ and $N cong D/(b)$ but i dont know what to do from here.Am i supposed to try create isomorphisms to prove that those invariant factors work? Any help is appreciated, Thanks.










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  • 1




    $begingroup$
    See math.stackexchange.com/a/2226275/589
    $endgroup$
    – lhf
    Dec 30 '18 at 10:51










  • $begingroup$
    Alright so i do have to create the isomorphism , thx !!! I was just wondering if there was another way to do it.
    $endgroup$
    – Pedro Santos
    Dec 30 '18 at 10:54
















1












$begingroup$


so i need some help. Imagine D is Principal Ideal Domain, and $M$ and $N$ are cyclic modules with order $a$ and $b$ respectevly, and $mdc(a,b)neq 1$. So im asked to prove that the invariant factors of $Mbigoplus N$ are the $gcd(a,b)$ and the $lcm(a,b)$. Im not quite sure how to do this, i know that $M cong D/(a)$ and $N cong D/(b)$ but i dont know what to do from here.Am i supposed to try create isomorphisms to prove that those invariant factors work? Any help is appreciated, Thanks.










share|cite|improve this question









$endgroup$








  • 1




    $begingroup$
    See math.stackexchange.com/a/2226275/589
    $endgroup$
    – lhf
    Dec 30 '18 at 10:51










  • $begingroup$
    Alright so i do have to create the isomorphism , thx !!! I was just wondering if there was another way to do it.
    $endgroup$
    – Pedro Santos
    Dec 30 '18 at 10:54














1












1








1





$begingroup$


so i need some help. Imagine D is Principal Ideal Domain, and $M$ and $N$ are cyclic modules with order $a$ and $b$ respectevly, and $mdc(a,b)neq 1$. So im asked to prove that the invariant factors of $Mbigoplus N$ are the $gcd(a,b)$ and the $lcm(a,b)$. Im not quite sure how to do this, i know that $M cong D/(a)$ and $N cong D/(b)$ but i dont know what to do from here.Am i supposed to try create isomorphisms to prove that those invariant factors work? Any help is appreciated, Thanks.










share|cite|improve this question









$endgroup$




so i need some help. Imagine D is Principal Ideal Domain, and $M$ and $N$ are cyclic modules with order $a$ and $b$ respectevly, and $mdc(a,b)neq 1$. So im asked to prove that the invariant factors of $Mbigoplus N$ are the $gcd(a,b)$ and the $lcm(a,b)$. Im not quite sure how to do this, i know that $M cong D/(a)$ and $N cong D/(b)$ but i dont know what to do from here.Am i supposed to try create isomorphisms to prove that those invariant factors work? Any help is appreciated, Thanks.







abstract-algebra modules principal-ideal-domains






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share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Dec 30 '18 at 10:35









Pedro SantosPedro Santos

817




817








  • 1




    $begingroup$
    See math.stackexchange.com/a/2226275/589
    $endgroup$
    – lhf
    Dec 30 '18 at 10:51










  • $begingroup$
    Alright so i do have to create the isomorphism , thx !!! I was just wondering if there was another way to do it.
    $endgroup$
    – Pedro Santos
    Dec 30 '18 at 10:54














  • 1




    $begingroup$
    See math.stackexchange.com/a/2226275/589
    $endgroup$
    – lhf
    Dec 30 '18 at 10:51










  • $begingroup$
    Alright so i do have to create the isomorphism , thx !!! I was just wondering if there was another way to do it.
    $endgroup$
    – Pedro Santos
    Dec 30 '18 at 10:54








1




1




$begingroup$
See math.stackexchange.com/a/2226275/589
$endgroup$
– lhf
Dec 30 '18 at 10:51




$begingroup$
See math.stackexchange.com/a/2226275/589
$endgroup$
– lhf
Dec 30 '18 at 10:51












$begingroup$
Alright so i do have to create the isomorphism , thx !!! I was just wondering if there was another way to do it.
$endgroup$
– Pedro Santos
Dec 30 '18 at 10:54




$begingroup$
Alright so i do have to create the isomorphism , thx !!! I was just wondering if there was another way to do it.
$endgroup$
– Pedro Santos
Dec 30 '18 at 10:54










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