Multiplying permutation cycles

In summary, the problem statement is asking for a permutation that is a product of disjoint cycles, but the answer key notation makes it unclear what a single permutation is.
  • #1
fishturtle1
394
82

Homework Statement


Compute each of the following products in ##S_9## (Write your answer as a single permutation).

a) (145)(37)(682)

Homework Equations


Theorem: Every permutation is either the identity, a single cycle, or the product of disjoint cycles.

The Attempt at a Solution



I start with (145)(37)(682).

Going from the rightmost cycle to the left, starting with 6.. 6 goes to 8, 8 goes to 8, then 8 goes to 8. So 6 goes to 8.

So i have (68) so far.

Now 8 goes to 2, 2 goes to 2, 2 goes to 2. So 8 goes to 2.

Now i have (682).

Now 2 goes to 6, 6 goes to 6, 6 goes to 6. So 2 goes to 6.

Now i have (6826) and I'm going to have a loop like (682682682...). I'm not sure where to go from here. If I just skip to 7, like (6827), then 2 goes to 7.. but 2 needs to go to 6 somehow. Also, by the theorem, its true that a permutation cannot be expressed as a single cycle and the product of disjoint cycles. Its a product of disjoint cycles..so is what I'm doing impossible?
 
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  • #2
Your original product is a product of disjoint cycles. I believe the problem statement parenthesis should be "your answer should only contain disjoint cycles". It is unclear what "single permutation" means.
 
  • #3
Orodruin said:
Your original product is a product of disjoint cycles. I believe the problem statement parenthesis should be "your answer should only contain disjoint cycles". It is unclear what "single permutation" means.
I asked here first to see if I could get a hint before looking at the answer key. It seems "single permutation" means the form:

##
\begin{pmatrix}
1 & 2 & 3 & 4 & 5 & 6 \\
1 & 2 & 3 & 4 & 5 & 6 \\
\end{pmatrix}
##

I can take it from here, sorry for the weird question, I was trying to avoid the answer key on the very first question..
 
  • #4
Ok, that makes sense. I just don't like that notation as it takes more space and is less transparent than cycle notation, but as a first exercise to get the hang of what it means I guess it is fine.
 

FAQ: Multiplying permutation cycles

1. What are permutation cycles?

Permutation cycles are a way of representing permutations, which are arrangements of elements in a specific order. A permutation cycle shows how elements are moved from one position to another within a permutation.

2. How do you multiply permutation cycles?

To multiply permutation cycles, you simply perform the operations of each cycle in order, starting with the rightmost cycle. This means that the elements are moved according to the first cycle, and then the resulting permutation is further modified by the second cycle, and so on.

3. What is the result of multiplying two permutation cycles?

The result of multiplying two permutation cycles is a single permutation cycle that represents the combined effect of both cycles. This resulting cycle shows how elements are moved based on the operations of both original cycles.

4. Can permutation cycles be multiplied in any order?

Yes, permutation cycles can be multiplied in any order. However, the resulting permutation may be different depending on the order in which the cycles are multiplied. It is important to follow the proper order of operations to accurately represent the desired permutation.

5. Are there any restrictions to multiplying permutation cycles?

There are no restrictions to multiplying permutation cycles as long as they have the same length. This means that the cycles must have the same number of elements and follow the same pattern of movement. If the cycles have different lengths, they cannot be multiplied together.

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