Norm of the ring












2












$begingroup$


What is the norm of



$$mathbb{Z}[zeta] = [a_0 + a_1zeta + ...+a_{l-2}zeta^{l-2} : a_i in mathbb{Z}],$$



for $(l leq 19)$ prime, and $zeta$ root of unity, so $mathbb{Z}[zeta]$ is UFD.



It is easy when $l=3$, $(a+bzeta)(a+bbar{zeta}) = a^2 - ab+ b^2$










share|cite|improve this question











$endgroup$












  • $begingroup$
    Not sure it is very easy : for a fixed element, would you not need to find the minimal polynomial or the conjugates of that element? For $l=3$ the conjugates were easy to find, but for larger $l$ this may be an issue.
    $endgroup$
    – астон вілла олоф мэллбэрг
    Aug 27 '18 at 12:05










  • $begingroup$
    Do you mean norm of an element, perhaps? (Note that UFDs may not be a Euclidean domain and so there may not be a Euclidean function)
    $endgroup$
    – daruma
    Aug 27 '18 at 13:42










  • $begingroup$
    @daruma, see Field norm
    $endgroup$
    – lhf
    Dec 17 '18 at 11:06










  • $begingroup$
    For $l=5$, see math.stackexchange.com/questions/24840/…. See also math.stackexchange.com/questions/175118/…
    $endgroup$
    – lhf
    Dec 17 '18 at 11:07


















2












$begingroup$


What is the norm of



$$mathbb{Z}[zeta] = [a_0 + a_1zeta + ...+a_{l-2}zeta^{l-2} : a_i in mathbb{Z}],$$



for $(l leq 19)$ prime, and $zeta$ root of unity, so $mathbb{Z}[zeta]$ is UFD.



It is easy when $l=3$, $(a+bzeta)(a+bbar{zeta}) = a^2 - ab+ b^2$










share|cite|improve this question











$endgroup$












  • $begingroup$
    Not sure it is very easy : for a fixed element, would you not need to find the minimal polynomial or the conjugates of that element? For $l=3$ the conjugates were easy to find, but for larger $l$ this may be an issue.
    $endgroup$
    – астон вілла олоф мэллбэрг
    Aug 27 '18 at 12:05










  • $begingroup$
    Do you mean norm of an element, perhaps? (Note that UFDs may not be a Euclidean domain and so there may not be a Euclidean function)
    $endgroup$
    – daruma
    Aug 27 '18 at 13:42










  • $begingroup$
    @daruma, see Field norm
    $endgroup$
    – lhf
    Dec 17 '18 at 11:06










  • $begingroup$
    For $l=5$, see math.stackexchange.com/questions/24840/…. See also math.stackexchange.com/questions/175118/…
    $endgroup$
    – lhf
    Dec 17 '18 at 11:07
















2












2








2





$begingroup$


What is the norm of



$$mathbb{Z}[zeta] = [a_0 + a_1zeta + ...+a_{l-2}zeta^{l-2} : a_i in mathbb{Z}],$$



for $(l leq 19)$ prime, and $zeta$ root of unity, so $mathbb{Z}[zeta]$ is UFD.



It is easy when $l=3$, $(a+bzeta)(a+bbar{zeta}) = a^2 - ab+ b^2$










share|cite|improve this question











$endgroup$




What is the norm of



$$mathbb{Z}[zeta] = [a_0 + a_1zeta + ...+a_{l-2}zeta^{l-2} : a_i in mathbb{Z}],$$



for $(l leq 19)$ prime, and $zeta$ root of unity, so $mathbb{Z}[zeta]$ is UFD.



It is easy when $l=3$, $(a+bzeta)(a+bbar{zeta}) = a^2 - ab+ b^2$







abstract-algebra






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Dec 17 '18 at 10:43









Namaste

1




1










asked Aug 27 '18 at 11:59









Dogukan.NDogukan.N

112




112












  • $begingroup$
    Not sure it is very easy : for a fixed element, would you not need to find the minimal polynomial or the conjugates of that element? For $l=3$ the conjugates were easy to find, but for larger $l$ this may be an issue.
    $endgroup$
    – астон вілла олоф мэллбэрг
    Aug 27 '18 at 12:05










  • $begingroup$
    Do you mean norm of an element, perhaps? (Note that UFDs may not be a Euclidean domain and so there may not be a Euclidean function)
    $endgroup$
    – daruma
    Aug 27 '18 at 13:42










  • $begingroup$
    @daruma, see Field norm
    $endgroup$
    – lhf
    Dec 17 '18 at 11:06










  • $begingroup$
    For $l=5$, see math.stackexchange.com/questions/24840/…. See also math.stackexchange.com/questions/175118/…
    $endgroup$
    – lhf
    Dec 17 '18 at 11:07




















  • $begingroup$
    Not sure it is very easy : for a fixed element, would you not need to find the minimal polynomial or the conjugates of that element? For $l=3$ the conjugates were easy to find, but for larger $l$ this may be an issue.
    $endgroup$
    – астон вілла олоф мэллбэрг
    Aug 27 '18 at 12:05










  • $begingroup$
    Do you mean norm of an element, perhaps? (Note that UFDs may not be a Euclidean domain and so there may not be a Euclidean function)
    $endgroup$
    – daruma
    Aug 27 '18 at 13:42










  • $begingroup$
    @daruma, see Field norm
    $endgroup$
    – lhf
    Dec 17 '18 at 11:06










  • $begingroup$
    For $l=5$, see math.stackexchange.com/questions/24840/…. See also math.stackexchange.com/questions/175118/…
    $endgroup$
    – lhf
    Dec 17 '18 at 11:07


















$begingroup$
Not sure it is very easy : for a fixed element, would you not need to find the minimal polynomial or the conjugates of that element? For $l=3$ the conjugates were easy to find, but for larger $l$ this may be an issue.
$endgroup$
– астон вілла олоф мэллбэрг
Aug 27 '18 at 12:05




$begingroup$
Not sure it is very easy : for a fixed element, would you not need to find the minimal polynomial or the conjugates of that element? For $l=3$ the conjugates were easy to find, but for larger $l$ this may be an issue.
$endgroup$
– астон вілла олоф мэллбэрг
Aug 27 '18 at 12:05












$begingroup$
Do you mean norm of an element, perhaps? (Note that UFDs may not be a Euclidean domain and so there may not be a Euclidean function)
$endgroup$
– daruma
Aug 27 '18 at 13:42




$begingroup$
Do you mean norm of an element, perhaps? (Note that UFDs may not be a Euclidean domain and so there may not be a Euclidean function)
$endgroup$
– daruma
Aug 27 '18 at 13:42












$begingroup$
@daruma, see Field norm
$endgroup$
– lhf
Dec 17 '18 at 11:06




$begingroup$
@daruma, see Field norm
$endgroup$
– lhf
Dec 17 '18 at 11:06












$begingroup$
For $l=5$, see math.stackexchange.com/questions/24840/…. See also math.stackexchange.com/questions/175118/…
$endgroup$
– lhf
Dec 17 '18 at 11:07






$begingroup$
For $l=5$, see math.stackexchange.com/questions/24840/…. See also math.stackexchange.com/questions/175118/…
$endgroup$
– lhf
Dec 17 '18 at 11:07












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