EBoard 08: Numbers (Section 1)

Warning! You are being recorded and transcribed, provided the technology is working correctly.

We are back to the standard start-of-class procedure.

Approximate optimistic overview

• Administrative stuff [10 min]
• About Wednesday’s quiz [10 min]
• Questions [5 min]
• Lab [50 min]
• Turn in lab [5 min]

Administrative stuff

Introductory notes

• Don’t forget that you can raise your hands during lab and either the mentor or I will wander over and try to help.
• Please do not use your electronic devices for anything other than classwork or a quick check of your email/texts. Anything else may lead to us defenestrating your device.
• My weekend fell apart a bit, so I’m a bit behind on everything. In particular, I haven’t looked at your pre-reflections or reading responses. Apologies!

Upcoming activities

Scholarly

• Thursday, 13 February 2025, 11:00 a.m.–Noon, JRC 101. Grinnell Lecture: Darrius Hills on “The Achievement of Identity: Soul Work, Salvation, and Black Manhood in the Religious Imagination of James Baldwin”.
• Tuesday, 18 February 2025, Noon–12:50 p.m., PDR 224C (White Dining Room). CS Table: ???

Artistic

• Tuesday, 11 February 2025, 4:00–5:00 p.m., Bucksbaum 131 (GCMoA). Gallery Talk with Chen, Kluber, and Tavares.
• Friday, 14 February 2025, 5:00–6:30 p.m. (talk at 6:00), 926 Broad St (Stewart Arts Building). Opening Reception for Artist Salon: Works by Grinnell College Art Majors

Multicultural

• Friday, 14 February 2025, 4:00–5:00 p.m., HSSC N1170 (Global Living Room) Middle of Everywhere: ???
• Saturday, 15 February 2025, ?:00-?:00 p.m., Harris Gym. Lunar New Year

Peer

Musical, theatric, sporting, and academic events involving this section’s students are welcome.

• Friday, 14 February 2025, 4:00–?. Field (of Dreams) House. Darren Young Classic.
• Saturday, 15 February 2025, 10:00–?. Field House. Darren Young Classic, Continued.

Wellness

• Tuesday, 11 February 2025, 12:15–12:50 p.m., GCMoA. Yoga in the Museum.
• Tuesday, 11 February 2025, 4:30–6:30 p.m., BRAC P103 (Multipurpose Dance Studio). Wellness Yoga.

Misc

• No particular date. Cyberspace. Fill out the survey at https://www.surveymonkey.com/r/GrinnellParksandRec.
• Tuesday, 11 February 2025, 7:00–8:00 p.m., Science 3820. Mentor Session.
• Sunday, 16 February 2025, 7:30–8:30 p.m., Science 3819. Mentor Session: Quiz and SoLA prep.
• Tuesday, 18 February 2025. 6:00–7:00 p.m., HSSC A1231. Make a Portfolio Website.
  • Please register at https://grinnell.joinhandshake.com/edu/events/1679688
• Tuesday, 18 February 2025, 7:00–8:00 p.m. No Mentor Session! (so no token)

Other good things

These do not earn tokens, but are worth your consideration.

Upcoming work

• Tuesday, 2025-02-10
  • Submit lab writeup for today’s lab
  • Readings for Wednesdays’s class.
    • Characters and strings
    • Symbolic values
  • Submit reading responses on Gradescope
• Wednesday, 2025-02-11
  • Quiz: Tracing
  • Makeup quiz: Decomposition
• Thursday, 2025-02-12
  • Readings for Friday’s class.
    • How Pair Programming Really Works (Wray)
    • Coping with Hitchhikers and Couch Potatoes on Teams (from B. Oakley et. al (2004).
      Turning Student Groups into Effective Teams.
      Journal of Student-Centered Learning 2 (1).)
    • Diverse Teams Feel Less Comfortable – and That’s Why They Perform Better
  • [Submit readings on Gradescope]
  • Mini-project 3 due
  • Submit mini-project 3 on Gradescope

About Wednesday’s Quiz

I will ask you to trace an expression that includes function calls. I expect you to trace one step at a time. Here’s an example.

Consider the following definitions.

(define x 10)
(define y 11)
(define f (lambda (x y) (* (+ x 2) (+ y 3))))

Trace the steps in evaluating (f (+ x y) (- x y)). We’ll do this together. One person does the next step, the next person says whether or not it looks good to them. And again, and again, and again.

    (f (+ x y) (- x y)))
--> (f (+ 10 y) (- 10 y))
--> (f (+ 10 11) (- 10 11))
--> (f 21 (- 10 11))
--> (f 21 -1)
--> (* (+ 21 2) (+ -1 3))
--> (* 23 (+ -1 3))
--> (* 23 2)
--> 46

• You can substitute all instances of one variable in one step.
• You should substitute all the arguments for the parameters in expanding a procedure call.
• If you have something like (* 2 3 4), you do it all at once.
• We won’t be using map, but if we were, you should do the full “apply the function to each argument” at once. (map sqr (list 1 2 3 4)) -> (list (sqr 1) (sqr 2) (sqr 3) (sqr 4)).
• What is (/ 2 3 4)? I’m pretty sure it’s the same as (/ (/ 2 3) 4) or 1/6. Similarly, (- 2 3 4) is (- (- 2 3) 4). All of these are left-associative.

Q&A

Administrative

How many tokens does it cost to make up a missed mini-project?

The token policy page says that it costs one. Note, however, that the “first redo” will be your only opportunity to earn an E, even though it’s effectively your first submission.

Readings

MP3

Lab

• Don’t forget to make a copy of the code!
• If you finish early, please do the extras.
• If you all make good progress on this lab, Sam will have some questions.

The behavior of round.

round rounds with the normal rules of “round to the nearest number”. .5 rounds up, below .5 rounds down?

(round 5/2) -> 3. Nope, it’s 2.

(round 7/2) -> 3. Nope, it’s 4.

What’s going on here? Answer: Good statistics. When it’s exactly halfway, you round towards the nearest even number.

Reminder: Experiment to understand!

Also: Computer scientists make some strange design decisions. (There are often design decisions behind weird behaviors.)

The behavior of max.

If any of the values are inexact, the result is inexact, even if the largest seems to be exact.

If all of the values are exact, the result is exact.

Why? If some of the numbers are inexact, it doesn’t make sense to get an exact number; you can’t get an exact number from an exact data set.

Sam’s example: Which is larger? 2^100 + 2 or 2.0^100 + 7.

Numerators and denominators of inexact numbers

You will see very strange numerators and denominators for inexact numbers.

1.2