Group Homomorphism Formula Isomorphism for Integer Sets

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In summary, the conversation discusses finding an isomorphism from the set of integers under multiplication mod 13 to the set of integers under addition mod 12. The conversation also touches on the difference between an isomorphism and a homomorphism. One person suggests using the operation tables to identify the mapping between the two sets, while another person suggests using the relation k->2^k to find the mapping. However, it is later determined that this method is not correct. Additionally, the decomposition theorem for group homomorphisms is briefly mentioned.
  • #1
dJesse
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I'm looking for a formula isomorphism from the set of integers under multiplication mod 13 to the set of integers under addition mod 12. I know the other way around it's easily expressed as a power of class 2. But this way I have no idea if its expressible as a formula.
 
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  • #2
That should be straightforward. Have you written down the operation tables for the two sets?
 
  • #3
I have now, but actually now I'm even doubting the isomorphism at itself. The only thing i can think of is something with a logarithm, base 2 cause that converts a 2 into 1 and a product into a sum. But i can't verify it cause it doesn't invert the mapping of the power of class 2.
 
  • #4
Why "isomorphism"? Your original question was only about a "homomorphism".
 
  • #5
Okay I'm sorry, the title is wrong, I'm looking for a isomorphism. (In the end I'm looking for a homomorphism from the integers under multiplication mod13 to the complex numbers length 1.)
 
  • #6
Well, that looks straight forward. When I write down the two operation tables I see several things: first the identity of {Z13,*} is 1 while the identity of {Z12, +} is 0. Any isomorphism must map 1 into 0. I notice that 12*12= 1 mod 13 and that 6+ 6= 0 mod 12. That is, that 12 and 6 have the property that they are there own inverses in the respective groups. Since they are the only values that have that property, 12 must map into 6: f(12)= 6 for an isomorphism from {Z13,*} to {Z12, +}. I then notice that 5*5= 12 mod 13 and that 3+ 3= 6 mod 12. Again, that tells me that f(5)= 3. Unfortunately, there is no n such that n*n= 5 mod 13 but I do see that 12*5= 8 mod 13 and 6+ 3= 9 mod 12. We must have f(8)= 12. Continuing in that way you should be able to identify f(n) for all n in Z13.
 
  • #7
Hey thanks for the stated reasoning. Now, I'm asking if it is also correct to just take the inverse of all the couples I get from the relation k->2^k, but then I get a different mapping from yours: f={(1,0),(2,1),(3,4),(4,2),(5,9),(6,5),(7,11),(8,3),(9,8),(10,10),(11,7),(12,6)}
 
  • #8
okay i found out it is not okay, but can you explain me why not? i thought the decomposition theorem for group homomorphisms sais it should be correct?

ps: i assume you meant f(8)=9
 
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1. What is a group homomorphism?

A group homomorphism is a function between two groups that preserves the group operation. In other words, if G and H are groups with binary operations * and + respectively, a function f: G → H is a group homomorphism if for all a, b ∈ G, f(a * b) = f(a) + f(b).

2. What is the group homomorphism formula?

The group homomorphism formula is the equation that describes the relationship between two groups under a homomorphism. It is f(a * b) = f(a) + f(b), where f is the homomorphism function, a and b are elements of the first group, and * and + are the binary operations of the first and second group respectively.

3. What is an isomorphism?

An isomorphism is a special type of homomorphism that is both one-to-one and onto, meaning it is a bijective function. In the context of group homomorphisms, an isomorphism preserves the group structure and is reversible, meaning there exists an inverse function that maps the elements back to the original group.

4. How is the group homomorphism formula used for integer sets?

The group homomorphism formula can be used to define a homomorphism between two groups of integers. For example, the function f(x) = 2x is a homomorphism between the group of integers and the group of even integers, as it preserves the group operation of addition.

5. What is the significance of group isomorphisms for integer sets?

Group isomorphisms for integer sets provide a way to compare and classify different groups of integers. They allow us to see if two groups have the same structure and thus are essentially the same group, even if their elements may be different. This can help us understand the underlying properties and relationships between different groups of integers.

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