EBoard 06 (Section 3): Conditionals
Approximate overview
- Administrative stuff [30 min]
- Questions [?? min]
- Lab [Approximately 50 min]
Administrivia
Introductory notes
- I forgot my hearing aids today. You may have to speak a bit louder.
(Or those in the front may have to repeat.)
- Starting today, I’ll use the “randomized calling cards” to call on
you. This is an opportunity for you to practice “thinking on your
feet”, as it were. Please try, but also feel free to say, “I’m
not sure.”
- Please say your name when you ask or answer a question (even if I’ve
just called you by name).
- Don’t forget that we have evening tutors available 7–10 p.m.
- Mentor sessions are now scheduled: Sunday 4–5 p.m., Monday 8–9 p.m.,
and Wednesday 8–9 p.m. All in the CS Commons.
- This week’s topics: Review quizzes 1 & 2; prep for Quiz 3.
- I’ve set up a semi-anonymous “check in” survey. Please take
the time to fill it out. https://bit.ly/csc-151-2022Sp-week02
- We do not have class Monday. It’s a “work differently” day.
(I’ll be working remotely.)
- A reminder: Please keep your mask on when working in 3813 or 3815
or any classroom.
- I realize that not everyone can make my office hours.
- Feel free to ask questions on Teams (or via email) at almost any
time.
- You can also propose times via the Microsoft Scheduling Assistant.
(Sam will demo.)
- While we remain at Code Blue, all office hours are via video chat
on Teams.
- Protocol: Sam texts “Are you ready?” You say “Yes”. Sam opens
a video chat.
- Alternate Protocol: You text “Are you ready?” I say “Yes”. One
of us opens a video chat.
Asking questions on Teams
- When submitting questions on Teams, please try to use the Q&A
channel, rather than direct chat, unless you are asking questions
about your code.
- There are more people who might reply.
- There are others who would benefit from your question.
- If possible, title your question.
- Sam often goes AFK after 8pm, sometimes earlier.
- If Sam is not AFK, he will answer.
- If Sam has insomnia, he might answer at strange times.
- AFK = “Away from Keyboard”
Racket notes / Debrief from last lab
Experimentation
- The
remainder exercise was intended to suggest that one way
we learn about procedures is to play/experiment with them.
(We’d hope that the documentation is clear, but it isn’t always.)
- The “four types of rounding” exercise was to encourage you to
play/experiment.
floor, ceiling, truncate, round
Types of numbers
- Complex: May have an imaginary part; may have a fractional part
- Real: No imaginary part, may have a fractional part
- Rational: No imaginary part, may have a fractional part
- Integer: No imaginary part, no fractional part
Notes
- All of these can be exact or inexact.
- Reals and rationals are indistinguishable.
- We tend to assume rationals are exact.
Rounding
What are the values of the following?
(round 7/2)(round 9/2)(round -7/2)(round -9/2)
First expermiment
> (round 7/2)
4
> (round 9/2)
4
Next experiment
(round 3/4)
1
(round 1/4)
0
(round 1/2)
0
(round 0.5)
0.0
(round -0.5)
-0.0
```
And another
> (round 1/2)
0
> (round 1/2)
0
> (round 1/2)
0
And another
> (round 1/2)
0
> (round 1/2)
0
> (round 3/2)
2
> (round 5/2)
2
> (round 7/2)
4
> (round 9/2)
4
> (round 11/2)
6
Hypothesis
- Odd + 1/2 rounds up
- Even + 1/2 rounds down
- When equidistant from two integers, rounds to the nearest even number.
Why?
- Results of rounding are now evenly divisible by two. Yay!
- Why not?
- A common statistical practice to deal with the issue that people
often respond with 1/2s, but we often store integers rather than reals.
- By rounding toward even, we hope to “balance out” the rounding
- Men’s shoe sizes: 10 10.5 10.5 11 11.5 11.5 12
- Average 11
- If we follow the round towards even policy, we get … 11
(because it’s a contrived example)
- If we follow the “round down only” policy, we get
- I tell you this because
- You should know what procedures do, even in weird cases
- There’s often a rationale for the behavior
Converting between exact and inexact
(inexact->exact (exact->inexact (expt 10 50)))- Once you’ve approximated, you’ve lost info. You can never regain it.
Upcoming work
- Quiz 2 due tonight at 10:30 p.m.
- Readings for Wednesday due Tuesday at 10:00 p.m.
- DDag question: Two important points from the readings.
- Lab writeup from today due Tuesday at 10:30 p.m.
- Ideally, you’ll finish that in class today.
- If not, set up a time to meet with your partners.
- If that’s not possible, finish (and submit) separately, but cite
your partner.
- Mini-Project 2 due Thursday at 10:30 p.m.
Upcoming Token-Generating Activities
Other Upcoming Activities
- Men’s Tennis 9am and 5pm Saturday in the Field House. (30 min of watching
is enough)
- Swim meet Saturday at 1pm. (30 min of watching is enough)
- Men’s Basketball Saturday at 1 p.m.
- Women’s Basketball Saturday at 3 p.m.
Friday PSA
- People care about you. Please take care of yourselves.
- Embrace moderation
- Don’t feel peer pressure; decide what is right for you
- Almost any choice you make is one others are also making
- Consent is essential
Reading Questions
I’ve started putting answers to the reading questions in the readings.
These are ones that didn’t naturally fit in a reading
Last night, I did not have time to review reading questions. You
can ask them, or other questions, now.
Other Questions
What happens if you did not get credit for the Decomposition quiz?
(Alternately, what happens if you do not get credit for the
Procedural Abstraction quiz?)
Don’t worry!
There will be a decomposition problem on SoLA 1. If you get it
right, you’ll now have achieved that learning objective. (Similar
answer for any topic.)
I’d recommend that you go to one of the mentor sessions before
SoLA 1 so that you are better prepared for the problem.
What happens if you got the Decomposition quiz wrong and you also get it
wrong on SoLA 1?
There will be a decomposition problem on SoLA 2. If you get it
right, you’ll now have achieved that learning objective.
But you should probably chat with me or a mentor or an evening tutor
before you take SoLA 2, so that we can be sure you understand the
core concepts. We can also assign you an individual tutor if that
will help (and you’re making use of other resources).
What happens if you got the Decomposition quiz wrong and you also get it
wrong on SoLA 1 and SoLA 2?
There will be a decomposition problem on SoLA 3. If you get it
right, you’ll now have achieved that learning objective.
Once again, you should get help before taking it again.
You’ll also have a chance on SolAs 4 and 5. We hope that’s not
necessary.
Lab
Preparation
During Lab
Wrapup
- Make sure to set up a time to meet with your partner to finish up the lab.