Math 422 Midterm Winter 2020
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Math 422 Midterm Winter 2020
Problem 1 [12 pts] Let C be the linear [7, k, d] code over F2 with generator matrix
(i) Find k and the number of codewords in C , with justification.
(ii) Find a parity check matrix for C in standard form. Hint: to check if you’ve made mistakes, multiply your parity-check matrix by the transpose of the given generator matrix.
(iii) Is C a Hamming code? Justify your answer.
(iv) Encode the message [1111].
(v) Suppose a codeword from C is sent and you receive the vector y = [0 0 0 0 1 1 0]. Decode y using syndrome decoding. Show your work by computing the syndrome of y with respect to the parity check matrix you found in part (ii) of this problem. Hint: this can be done without writing down a syndrome table.
Problem 2 [10 pts] Consider the 3-ary (defined over Z/3Z) code
. Note that we are listing all of the codewords of C here. Also, double check your work to catch mistakes.
(i) Determine d(C). Show your work.
(ii) How many errors can C detect? How many errors can C correct?
(iii) Suppose a codeword is transmitted and y = [10001] is received. Decode y using nearest neighbor decoding if possible. If it is not possible (or ambiguous as we called it in class), then explain why it is not possible.
Problem 3 [10 pts]
(i) Does there exist a digit ? such that
0 一 13 一 1?9139 一 9
is an ISBN-10 code? Find the digit ? if it is possible. Otherwise, explain why it is not possible.
(ii) Find all xl, x2 such that xl 一 13 一 32x2870 一 0
is an ISBN-10 code. Your answer will involve finding a relation between xl and x2 .
Problem 4 [10 pts] Let q = p for some prime p ↓ N and α ↓ N. We can consider the fi- nite field Fg with q elements.
(i) Let n ↓ N. Briefly, define the Hamming code Ham(n, q) along with an associated Hamming matrix H.
(ii) Let n ↓ N and set m = (qn 一 1)/(q 一 1). Let C be a q-ary linear [m, m 一 n, 3] code (this means that C ↓ Fg(m), dim(C) = m 一 n, and d(C) = 3). Prove that C is isomorphic to Ham(n, q). Hint: what can you say about a parity-check matrix for C, and how does this relate to the definition of a Hamming matrix
2022-02-14