Group Homomorphism: True or False?

  • MHB
  • Thread starter lemonthree
  • Start date
  • Tags
    Group
In summary, a group homomorphism is a function between two groups that preserves the group operation. To determine if a function is a group homomorphism, you need to check if it preserves the group operation. It can be both one-to-one and onto, but not always. Not every function between two groups is a group homomorphism, as it must preserve the group operation. There are different types of group homomorphisms, such as isomorphisms, endomorphisms, and automorphisms.
  • #1
lemonthree
51
0
Consider the group
(\mathbb{R}^*,\times)
.


"The map
\psi:\mathbb{R}^*\to\mathbb{R}^*
defined by
\psi(x)=|x|
for all
x\in \mathbb{R}^*
is a group homomorphism."

Is this true or false? I'm guessing it's true because
φ (j) = | j |, which means
φ (j * k) = | j * k |
=| j | * | k |
= φ ( j ) * φ ( k ).
 
Physics news on Phys.org
  • #2
Hi lemonthree,

That is true, but you should also check that
  • $\phi(x^{-1}) = \phi(x)^{-1}$
  • $\phi(1) = 1$
 

1. What is a group homomorphism?

A group homomorphism is a function between two groups that preserves the group structure. This means that the operation in the first group is preserved in the second group. In other words, if we apply the function to two elements in the first group and then perform the group operation, it will be the same as applying the function to the two elements separately and then performing the group operation.

2. How do you determine if a function is a group homomorphism?

To determine if a function is a group homomorphism, we need to check if it preserves the group structure. This means that for any two elements a and b in the first group, the function must satisfy f(a * b) = f(a) * f(b), where * represents the group operation. If this condition is met, then the function is a group homomorphism.

3. Can a function be a group homomorphism if it is not injective or surjective?

No, a function must be both injective (one-to-one) and surjective (onto) to be a group homomorphism. This is because a group homomorphism must preserve the group structure, and if the function is not injective, then different elements in the first group will map to the same element in the second group, which breaks the group structure. Similarly, if the function is not surjective, then there will be elements in the second group that are not mapped to by any element in the first group, also breaking the group structure.

4. Are there different types of group homomorphisms?

Yes, there are different types of group homomorphisms such as monomorphisms, epimorphisms, and isomorphisms. A monomorphism is an injective group homomorphism, an epimorphism is a surjective group homomorphism, and an isomorphism is a bijective group homomorphism. These different types have different properties and are useful for different purposes in group theory.

5. Is the statement "all group homomorphisms are isomorphisms" true or false?

False. While all isomorphisms are group homomorphisms, not all group homomorphisms are isomorphisms. An isomorphism is a bijective group homomorphism, meaning it is both injective and surjective. However, a group homomorphism can be either injective or surjective, but not necessarily both. Therefore, not all group homomorphisms are isomorphisms.

Similar threads

  • Linear and Abstract Algebra
Replies
1
Views
755
  • Linear and Abstract Algebra
Replies
3
Views
1K
Replies
11
Views
2K
  • Linear and Abstract Algebra
Replies
2
Views
4K
  • Linear and Abstract Algebra
Replies
9
Views
893
  • Linear and Abstract Algebra
Replies
1
Views
886
  • Linear and Abstract Algebra
Replies
3
Views
788
  • Linear and Abstract Algebra
Replies
11
Views
3K
  • Linear and Abstract Algebra
Replies
2
Views
1K
  • Linear and Abstract Algebra
Replies
1
Views
1K
Back
Top