CS 242, Section 002 Sonoma State University Spring, 2026
 
Discrete Structures for Computer Science
Instructor: Henry M. Walker

Lecturer, Sonoma State University
Professor Emeritus of Computer Science and Mathematics, Grinnell College

Notes:


Assignment 7 (Gates, Circuits, and Indexed Mathematical Elements

  1. Interpreting Combinatorial Circuits: Find the output of each of the following combinatorial circuits.

    combinatorial circuits
  2. Constructing Combinatorial Circuits: Construct combinatorial circuits from input bits p, q, and r, using inverters, OR gates, and AND gates to produce each of the following outputs.

    1. (p ∧ q) ∨ (¬ p ∧ r)
    2. ((¬ p ∧ ¬ q) ∧ r) ∨ ((p ∧ q) ∧ r)
  3. Manipulating Indexed Mathematical Elements:
    Section 6.3 presents summation formulae for \( \sum_{i=1}^n i \) and \( \sum_{i=0}^n r^i \) . A more extensive collection of summation formulae is available from this link.
    Note that the first of these expressions starts with i=1, whereas the second begins with i=0!

    Although this notation can be convenient when doing mathematics-related work (such as often arises in CS 415, Analysis of Algorithms), use and interpretation of this notation can require some practice. In the following, consider n to be a positive integer, unless otherwise specified.

    1. What is the difference in total value between the sums \( \sum_{i=0}^n i \) and \( \sum_{i=1}^n i \) .

    2. Use the summation formulae from the book or the above link to find a closed form for \( \sum_{i=1}^5 i \).

    3. Use the summation formulae from the book or the above link to find a closed form for \( \sum_{i=1}^{25} i \).

    4. Use the summation formulae from the book or the above link to find a closed form for \( \sum_{i=1}^n i \) .
      Show that your answer to this part matches your answer from part b, when n=5.

    5. Use the summation formulae from the book or the above link to find a closed form for \( \sum_{i=1}^{n^2} i \) .
      Show that your answer to this part matches your answer from part c, when n=5.

    6. Use the summation formulae from the above link to find a closed form for \( \sum_{i=1}^{n} i^3 \) .

    7. Use the summation formulae from the above link to find a closed form for \( \sum_{j=1}^{k} j^3 \) .

    8. Use the summation formulae from the above link to find a closed form for \( \sum_{j=1}^{n^2} j^3 \) .


created October 25, 2025
revised October-November, 2025
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For more information, please contact Henry M. Walker at walker@cs.grinnell.edu.