Understanding Rings: Example of Homomorphism/Isomorphism

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In summary, a homomorphism is a mapping between two algebraic structures that preserves operations, while an isomorphism also preserves structure. An example of a homomorphism is the mapping between integers and even integers under addition. To prove two structures are isomorphic, a one-to-one and onto mapping must be shown to preserve operations and structure. Not all homomorphisms are isomorphisms, as some may not preserve structure. Homomorphisms and isomorphisms are useful in understanding rings by allowing for comparison and generalization between different rings.
  • #1
corkycorey101
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Can you give an example of two rings R and S, and a function f:R⟶S such that f(ab)=f(a)f(b) for all a,b ∈ R, but f(a+b)≠f(a)+f(b) for some a,b ∈ R. I know that it has to do with proving homomorphisms/isomorphisms but am confused how to come up with the actual example.
 
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  • #2
Let $R = S =\Bbb Z$, the ring of integers, and set:

$f(k) = k^2$.
 
  • #3
Oh wow, that was easier than I thought. I was way over thinking it. Thank you so much!
 

Related to Understanding Rings: Example of Homomorphism/Isomorphism

1. What is the difference between a homomorphism and an isomorphism?

A homomorphism is a mapping between two algebraic structures that preserves the algebraic operations. This means that the result of applying the operation on two elements in the first structure will be the same as applying the operation on the corresponding elements in the second structure. An isomorphism, on the other hand, not only preserves the operations but also the structure of the two structures. This means that an isomorphism is a one-to-one and onto mapping between two structures, and all properties of the first structure can be found in the second structure as well.

2. Can you give an example of a homomorphism?

Yes, an example of a homomorphism is the mapping between the set of integers under addition and the set of even integers under addition. The mapping is defined as f(x) = 2x, where x is an integer. This mapping preserves the addition operation, as the sum of two integers in the first set will be mapped to the sum of their corresponding even integers in the second set.

3. How do you prove that two structures are isomorphic?

To prove that two structures are isomorphic, you need to show that there exists a one-to-one and onto mapping between the two structures that preserves the operations and structure. This can be done by explicitly defining the mapping and showing that it satisfies the criteria for an isomorphism.

4. Are all homomorphisms also isomorphisms?

No, not all homomorphisms are isomorphisms. A homomorphism only preserves the operations, while an isomorphism also preserves the structure. This means that there may be elements in the first structure that are not mapped to any element in the second structure, making it a homomorphism but not an isomorphism.

5. How are homomorphisms and isomorphisms useful in understanding rings?

Homomorphisms and isomorphisms are useful tools in understanding rings because they allow us to compare and study different rings. By identifying homomorphisms and isomorphisms between two rings, we can determine if they have similar properties and structures. This can help us make connections and generalize results from one ring to another, making it easier to understand the properties and behaviors of rings in general.

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