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Worksheet Weekly Practice 13
Instructions: You may type up or handwrite your work, but it must be neat, professional, and organized and it must be saved as a PDF file and uploaded to the appropriate Gradescope assignment. Use a scanner or scanning app to convert handwritten work on paper to PDF. I encourage you to type your work using the provided template.
All tasks below must have a complete solution that represents a good-faith attempt at being right to receive engagement credits. If your submission is complete and turned in on time, you will receive full engagement credit for the assignment. All other submissions will receive zero engagement credit. Read the guidelines at Grading Specifications carefully.
To abide by the class academic honesty policy, your work should represent your own understanding in your own words. If you work with other students, you must clearly indicate who you worked with in your submission. The same is true for using tools like generative AI although I strongly discourage you from using such tools since you need to build your own understanding here to do well on exams.
True/False, Multiple Choice, & Fill-In.
For these problems a justification is not required for credit, but it may be useful for your own understanding to include one. True/False problems should be marked True if the statement is always true, and False otherwise. Multiple choice problems may have more than one correct answer if that is indicated in the problem statement; be sure to select all that apply. Fill-in problems require a short answer such as a number, word, or phrase.
2.
Fill-In: Cyclic codes of length \(n\) over \(\F_q\) are in 1-to-1 correspondence with of \(x^n-1\) over \(\F_q\text{.}\)
3.
True/False: All cyclic codes have a systematic generator matrix.
Short Response.
Your responses to these questions should be complete solutions with justifications, as per the Grading Specifications.
4.
Hint.
\(x^{21}-1\) factors over \(\F_2\) as the product of irreducible polynomials which are minimal polynomials for elements of order \(1,3,7,21\text{.}\) We have handled the first three of these already this semester; so you just need to work out what degree the polynomials for the order \(21\) elements (which first lie in \(\F_{2^6}\) but are not primitive in that field) are. Remember that for this problem you do not actually need to know the factors; just how many there are.
5.
Determine the generator polynomial, check polynomial, and dimension of the smallest cyclic code containing the vector \(\vec{v}=(112\, 110)\) in \(\F_3^6\text{.}\)
6.
Let \(C_1 \) and \(C_2\) be cyclic codes of length \(n\) over \(\F_q\) with generator polynomials \(g_1(x)\) and \(g_2(x)\text{.}\)
(a)
(b)
Show that \(C_1 + C_2 = \{\vec{c}_1+\vec{c}_2 \mid \vec{c}_1\in C_1, \vec{c}_2\in C_2\}\) is a cyclic code of length \(n\) and find its generator polynomial.
