CSCI 470 Spring 2015
Languages and Machines
Archived Class
Charles Cusack
Computer Science
Hope College
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Homework 13

General Comments

  • Problems are taken from the textbook unless otherwise noted.
  • For full credit, provide context for each problem, show all calculations, and explain your work/answers.
  • Numbers and/or algebra by themselves are not enough.
  • You will lose a significant amount of credit if you do not show enough work/context for your answers.
  • Precision is very important. You cannot skip steps, make guesses, or use flawed logic. Any of these things can lead to incorrect answers.
  • Homework assignments must be very neatly written or typeset (e.g. using Word or OpenOffice).
  • You must indicate any assistance you had on an assignment as specified on the Policies page.

Details

ProblemComments
7.7You only need to prove closure under union. This one is really easy--You essentially need to re-prove an exercise from chapter 3 (for which a solution is given) with the added requirement to show that the polynomial time requirement is satisfied.
7.9This one is really easy if you don't over think it.
7.12You have two choices:
  1. Give a NTM that decides the language.
  2. Define a certificate for the problem and explain how it can be used to verify that the two graphs are isomorphic.
In both cases, you need to argue that they are polynomial-time. Notice that you only need to prove that it is NP, not that it is NP-complete.
7.20Make sure to answer both questions, and do so separately. You may use the result of exercise 7.18 if you think it helps.
7.21bMake sure you show that it is both NP and NP-Hard. For the NP-Hard part, give a TM that computes the reduction and prove that it is indeed a reduction, and argue that it is a polynomial reduction. There is an easy reduction if you choose the right problem to reduce from.