Number of Non-Isomorphic Abelian Groups

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In summary: I think the proof is pretty simple, but I can't remember it off the top of my head. I'll need to look it up.In summary, the largest possible order an element of Z_3 x Z_3 can have is 6 (= lcm{2,3}).
  • #1
apalmer3
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Homework Statement


Determine the number of non-isomorphic abelian groups of order
72, and list one group from each isomorphism class.


The Attempt at a Solution



72 = 2^3*3^2
3= 1+1+1= 2+1= 3 (3)

2= 1+1= 2 (2)

3*2 = 6

And then I get lost on the listing of a group from each isomorphism class... Help?
 
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  • #2
Do you know the fundamental theorem of finite abelian groups? If you really understand it, this should be straightforward.
 
  • #3
The fundamental theorem of finite abelian groups states that every finite abelian group can be expressed as the direct sum of cyclic subgroups of prime-power order.

Z_2 x Z_2 x Z_2 x Z_3 x Z_3
Z_2 x Z_2 x Z_2 x Z_9
Z_2 x Z_4 x Z_3 x Z_3
Z_2 x Z_4 x Z_9
Z_8 x Z_3 x Z_3
Z_8 x Z_9

Yes?
 
  • #4
Yes, those are precisely all of them.
 
  • #5
Okay. Thanks so much! I was trying to make it more complicated than it needed to be, I think. :-D

This is a side question that kind of pertains to this. Why is Z_3 x Z_3 not isomorphic to Z_9?

Thanks again for your help, Morphism! You're a lifesaver! (I have a test in less than 10 hours... *sigh*)
 
  • #6
Well, for instance, notice that Z_3 x Z_3 doesn't have an element of order 9.

Good luck on your test!
 
  • #7
Thanks for the luck! I'm probably going to need it.

Is there a simple way to test whether or not something has an element of a certain order (i.e. Z_3 x Z_3 not having an element of order 9)? I want to make sure I understand this fully before morning.

Thanks again!
 
  • #8
Try to prove that the order of an arbitrary element (x,y) in GxH is lcm{o(x), o(y)}. Can you generalize this to the direct product of n groups?

So in our case, the largest possible order an element of Z_3 x Z_3 can have is 6 (= lcm{2,3}).
 
  • #9
Good Morning, Morphism!

I'm looking at this last post, and I'm still a bit confused (forgive me). How did you decide that for Z_3 x Z_3 we were using lcm{2,3}?

Thank you so much for your time and patience. :-D
 

1. What is the definition of a non-isomorphic abelian group?

A non-isomorphic abelian group is a type of mathematical structure that satisfies the commutative property, meaning that the order in which elements are multiplied does not affect the result. Additionally, a non-isomorphic abelian group is not the same as any other abelian group, meaning that it has a unique structure and cannot be transformed into another abelian group through rearrangement of its elements.

2. How many non-isomorphic abelian groups exist?

The number of non-isomorphic abelian groups is infinite. However, there are certain patterns and relationships that can be used to categorize and classify these groups.

3. What is the significance of studying the number of non-isomorphic abelian groups?

Studying the number of non-isomorphic abelian groups is important because it helps us understand the structure and behavior of these groups, which have many applications in mathematics, physics, and computer science. It also allows us to identify and classify different types of abelian groups, which can aid in solving complex problems and developing new mathematical theories.

4. How do you determine whether two abelian groups are isomorphic or not?

To determine whether two abelian groups are isomorphic, we look at their structure and elements. If the two groups have the same number of elements and their operations (addition and multiplication) behave in the same way, then they are isomorphic. However, if there is even one difference in their structure or operations, then they are not isomorphic.

5. Can non-abelian groups also be non-isomorphic?

Yes, non-abelian groups can also be non-isomorphic. This means that they have different structures and cannot be transformed into each other through rearrangement of elements. Non-abelian groups and abelian groups are two different types of mathematical structures, and they can have different numbers of non-isomorphic groups within each type.

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