EBoard 06: Numbers

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

Approximate overview

• Quiz [15 min]
• Administrative stuff [15 min]
• Q&A [15 min]
• Lab [30 min]
• Turn in lab [5 min]

Administrative stuff

• Is 7pm or 8pm better for Thursday mentor sessions?
  • 7pm Many
  • 8pm Fewer
  • Undecicded Similar to 8pm

Welcome to new class members!

• We met one new class member on Wednesday.
• We have two new class members to meet today.

TPS: What should they know about the class?

• More than you could ever hope to catch up on. Drop now. (That was a joke.)
• There’s a start-of-class process. Grab a card. Figure out which computer it is. Drop the card in the bucket. Navigate to the computer. If you are first, log in. When both partners arrive, introduce yourselves and chat about important things like your work habits and skills.
  • Exception 1: Sometimes we do two-day labs. In those cases, plan to return to the same place.
  • Exception 2: On Fridays, you should also grab a quiz.
  • Exception 3: Sam sometimes puts others instructions on the whiteboard, so look up and read the whiteboard when you enter class.
• Sam is incredibly cruel and will eat away at your self confidence by insulting your answers.
• Until everyone learns your name, say your name when you ask or answer a question, even if Sam has just called on you by name.

Token activities

Scholarly

Cultural

Peer

• Friday, 2024-02-02, 8pm, Harris Concert Hall: Weekend Murder Mystery. There’s food. You get to solve puzzles. The winner(s) will get prizes.
• Saturday, 2024-02-03, 1pm?, Natatorium: Swim meet.

Wellness

Misc

• InfoSec security survey (coming via email)

Other good things

Upcoming work

• Friday, 2024-02-02, 11pm: Mini-project 1 post-refelection due.
• Friday, 2024-02-02, 11:00pm: Mini-project 2 pre-reflection due.
• No readings for Monday! (Please don’t try to do Wednesday’s readings ahead.)
• Monday, 2024-02-05, 8:30am: Submit today’s lab writeup.
  • Submit on Gradescope
  • Preferred: Submit before the end of class today.
• Wednesday, 2024-02-07, 11:00pm: Mini-Project 2 due.
  • Gradescope forthcoming.

Friday PSA

• Moderation is essential.
• Please decide what is right for you.
• Take care of yourselves.
• Consent is essential.

Questions

Administrative

Reading

What’s with this 'solid in the symbols reading?

It’s something we used in the old image libary. Sam forgot to edit the reading.

Why do we learn symbols?

Mostly so that you learn why we write things like 'symbol. We may return to them later in the semester.

Can you compare symbols?

You can compare them to each other for equality, but they are not ordered.

No symbol equals any number.

What’s the difference between a symbol and a string?

Symbols are “atomic”; you cannot decompose a symbol into component parts.

Strings are “compound”; you can decompse a string into smaller strings, extract letters, etc.

You can also compare strings according to a “natural” ordering. For example, “apple” should be before “zebra” in the ordering most of us use.

Can you give an example of when you’d use symbols instead of strings?

Not at the moment. Stay tuned.

MP2

I can’t find equilateral triangles. Should I use 2htdp/image?

NO.

Perhaps your 151 library is out of date. Update it.

I can’t find solid-right-triangle.

That’s intentional. You’re writing it!

Lab

All of today’s problems are “think and try” rather than “write a procedure”. Hence, the autograder will only check that the file exists.

What do you expect to get for (* (sqrt 2) (sqrt 2))?

2

Do you get 2?

No

What’s the difference?

Um (- 2 (* sqrt 2) (sqrt 2)).

Which is something like 4.001212e-16. I don’t know what that means.

It means 4.001212 * 10 to the -16, or .000000000000004001212.

Inexact numbers

Some fun things to try

> (define x (expt 2 100))
> (define ex (exact->inexact x))
> x
> ex
> (+ x 1)
> (+ ex 1)
> (- (+ x 1) 1)
> (- (+ ex 1) 1)