Chapter 16: Problem 1
Let \(G=S_{4}\). (a) For \(\alpha=\left(\begin{array}{llll}1 & 2 & 3 & 4 \\ 2 & 3 & 4 & 1\end{array}\right)\), find the subgroup \(H=\langle\alpha\rangle\). (b) Determine the left cosets of \(H\) in \(G\).
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Chapter 16: Problem 1
Let \(G=S_{4}\). (a) For \(\alpha=\left(\begin{array}{llll}1 & 2 & 3 & 4 \\ 2 & 3 & 4 & 1\end{array}\right)\), find the subgroup \(H=\langle\alpha\rangle\). (b) Determine the left cosets of \(H\) in \(G\).
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If \(G\) is a group of even order, prove that there is an element \(a \in G\) with \(a \neq e\) and \(a=a^{-1}\).
Express each of the following elements of \(S_{7}\) as a product of disjoint cycles. $$ \begin{aligned} \alpha &=\left(\begin{array}{lllllll} 1 & 2 & 3 & 4 & 5 & 6 & 7 \\ 2 & 4 & 6 & 7 & 1 & 5 & 3 \end{array}\right) \\ \beta &=\left(\begin{array}{lllllll} 1 & 2 & 3 & 4 & 5 & 6 & 7 \\ 3 & 6 & 5 & 2 & 1 & 7 & 4 \end{array}\right) \\ \gamma &=\left(\begin{array}{lllllll} 1 & 2 & 3 & 4 & 5 & 6 & 7 \\ 2 & 3 & 1 & 7 & 5 & 4 & 6 \end{array}\right) \\ \delta &=\left(\begin{array}{lllllll} 1 & 2 & 3 & 4 & 5 & 6 & 7 \\ 4 & 2 & 7 & 1 & 3 & 6 & 5 \end{array}\right) \end{aligned} $$
Let \(H\) and \(K\) be subgroups of a group \(G\), where \(e\) is the identity of \(G\). a) Prove that if \(|H|=10\) and \(|K|=21\), then \(H \cap K=\\{e\\}\). b) If \(|H|=m\) and \(|K|=n\), with \(\operatorname{gcd}(m, n)=1\), prove that \(H \cap K=\\{e\\}\)
a) Construct a decoding table (with syndromes) for the group code given by the generator matrix $$ G=\left[\begin{array}{lllll} 1 & 0 & 1 & 1 & 0 \\ 0 & 1 & 0 & 1 & 1 \end{array}\right] $$ b) Use the table from part (a) to decode the following received words. \(\begin{array}{cccc}11110 & 11101 & 11011 & 10100 \\ 10011 & 10101 & 11111 & 01100\end{array}\) c) Does this code correct single errors in transmission?
The \((5 m, m)\) five-times repetition code has encoding function \(E: \mathbf{Z}_{2}^{m} \rightarrow \mathbf{Z}_{2}^{5 m}\), where \(E(w)=w w w w w .\) Decoding with \(D: \mathbf{Z}_{2}^{5 m} \rightarrow \mathbf{Z}_{2}^{m}\) is accomplished by the majority rule. (Here we are able to correct single and double errors made in transmission.) a) With \(p=0.05\), what is the probability for the transmission and correct decoding of the signal \(0 ?\) b) Answer part (a) for the message 110 in place of the signal \(0 .\) c) For \(m=2\), decode the received word $$ r=0111001001 $$ d) If \(m=2\), find three received words \(r\) where \(D(r)=00\). e) For \(m=2\) and \(D: \mathbf{Z}_{2}^{10} \rightarrow \mathbf{Z}_{2}^{2}\), what is \(\left|D^{-1}(w)\right|\) for each \(w \in \mathbf{Z}_{2}^{2} ?\)
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