Chapter 2: Problem 33
Construct Cayley digraphs of the indicated group \(G\) with the indicated generating set \(S\), and specify the defining relations. $$ G=S_{3} \quad S=\\{(12),(23)\\} $$
Short Answer
Expert verified
Construct a digraph with nodes from \(S_3\) and edges from \( (12) \) and \( (23) \). Define relations: \((12)^2 = e\), \((23)^2 = e\), \((12)(23)(12) = (123)\), and \((23)(12)(23) = (132)\).
Step by step solution
01
Identify the Group Elements of \(S_3\)
The symmetric group \(S_3\) consists of all permutations of three elements. The elements are: the identity \(e\), \((12)\), \((13)\), \((23)\), \((123)\), and \((132)\).
02
Define the Generators \(S\) and Apply Them to \(S_3\)
The generators are \((12)\) and \((23)\). These generators allow us to reach each element of \(S_3\) starting from the identity by applying these permutations iteratively.
03
Construct the Cayley Digraph for \(S_3\) with Generating Set \(S\)
Create a directed graph (digraph) where each vertex represents an element of \(S_3\). Draw directed edges based on the operation of the generators:- From any node \(g\), draw an edge to \(g \cdot (12)\) and \(g \cdot (23)\).- For example, from the identity \(e = ()\), we draw an edge to \((12)\) and \((23)\).- Continue this process for all nodes ensuring all group elements are connected.
04
Specify the Defining Relations of \(S_3\)
The defining relations for \(S_3\) with the given generators \((12), (23)\) are:1. \((12)^2 = e\)2. \((23)^2 = e\)3. \((12)(23)(12) = (123)\)4. \((23)(12)(23) = (132)\)
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Symmetric Group S3
The symmetric group \(S_3\) is an important concept in group theory. It consists of all possible permutations of three distinct objects.
This group has six elements, which include:
This group has six elements, which include:
- The identity permutation \(e\) which does nothing to the set.
- The transpositions \((12), (13), (23)\) which swap two elements.
- The cyclic permutations \((123)\) and \((132)\) which rearrange the entire set in cycles.
Group Generators
In group theory, the concept of generators is crucial for understanding how groups function. A set of generators can help describe the entire group by using these generators in various combinations.
In the context of \(S_3\), the generators \((12)\) and \((23)\) are used. With these generators:
In the context of \(S_3\), the generators \((12)\) and \((23)\) are used. With these generators:
- Every element of \(S_3\) can be reached from the identity element \(e\) by a sequence of these operations.
- \((12)\) swaps the first two elements.
- \((23)\) swaps the last two elements.
Defining Relations
Defining relations are equations that relate the generators of a group with each other and with the identity element. They are critical in fully describing the structure of a group.
For \(S_3\) with generators \((12)\) and \((23)\), the defining relations include:
For \(S_3\) with generators \((12)\) and \((23)\), the defining relations include:
- \((12)^2 = e\) and \((23)^2 = e\) because each generator is its own inverse.
- \((12)(23)(12) = (123)\) which shows how combinations of generators produce other elements of the group.
- \((23)(12)(23) = (132)\) that also helps in describing the cycling behavior of permutations.
Permutation Group
A permutation group is a set of permutations that can be performed on a set and forms a group under the operation of composition.
The symmetric group \(S_3\) is a classic example of a permutation group because it includes all permutations for three elements. Key characteristics include:
The symmetric group \(S_3\) is a classic example of a permutation group because it includes all permutations for three elements. Key characteristics include:
- Closure: If you compose any two elements of the group, the result is still an element of the group.
- Associativity: The order of applying permutations doesn't change the final outcome, as long as the sequence is preserved.
- Identity: There exists a neutral element \(e\) that doesn't change any element it is applied to.
- Inverses: Each permutation has an inverse permutation that "undoes" it, resulting in the identity.
Directed Graphs
Directed graphs, or digraphs, are graphs where the edges have a direction associated with them. In the context of Cayley digraphs, they represent group elements and the actions of generators.
For \(S_3\) with the generating set \(\{(12), (23)\}\):
For \(S_3\) with the generating set \(\{(12), (23)\}\):
- Vertices represent elements of the group.
- Directed edges represent the application of generators.
- An edge from node \(g\) to \(g \cdot (12)\) or \(g \cdot (23)\) showcases how you can "move" from one group element to another using a generator.