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Subject: "Gaussian factorisation"     Previous Topic | Next Topic
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Tibi
guest
Sep-02-05, 06:32 AM (EST)
 
"Gaussian factorisation"
 
   There is a unique factorisation theorem for Gaussian integers.
I factorised 20 in two different ways:

(1) -1*(2+i)*(2-i)*(1+i)^4, and
(2) -1*(2+i)*(2-i)*(1-i)^4.

If I understood the concept of Gaussian primes correctly, then all the factors in (1) and (2) are primes (and -1 is a unit). The two factorisations are different. Then how does the unique factorisation theorem hold?


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alexbadmin
Charter Member
1636 posts
Sep-02-05, 07:43 AM (EST)
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1. "RE: Gaussian factorisation"
In response to message #0
 
   >(1) -1*(2+i)*(2-i)*(1+i)^4, and
>(2) -1*(2+i)*(2-i)*(1-i)^4.
>
>Then how does the unique factorisation theorem hold?

The factorization is unique up to the factors of unity. i is one such, and since

i·(1 - i) = 1 + i,

there is no contradiction.


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Tibi
guest
Sep-02-05, 10:39 AM (EST)
 
2. "RE: Gaussian factorisation"
In response to message #1
 
   Thank you.
Does it mean that 1+i is not a Gaussian prime?

Something else that I would be grateful for : if somebody could please suggest a Gaussian factorisation algorithm.

Thanks


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alexbadmin
Charter Member
1636 posts
Sep-02-05, 11:59 AM (EST)
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3. "RE: Gaussian factorisation"
In response to message #2
 
   >Thank you.
>Does it mean that 1+i is not a Gaussian prime?

No, why? 1+i is a Gaussian prime because

N(1+i) = (1+i)(1-i) = 2

is a (regular) prime, see

https://www.cut-the-knot.org/arithmetic/int_domain2.shtml

>Something else that I would be grateful for : if somebody
>could please suggest a Gaussian factorisation algorithm.

At the same link you can find an idea that leads to a factorization algorithm.


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