Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Reading check.
• Behind the scenes: How Scheme implements vectors.
• Lab.

Preliminaries

Admin

• New partners (some cards may be missing, so we'll adapt)!
• Review sessions
  • Tonight at 8pm with Alex
  • Tomorrow at 8pm with Ajuna
  • Tomorrow at 10am with SamR

Upcoming Work

• Lab writeup: Exercise 5, http://bit.ly/151-2014F-w40
• Readings for Friday:
  • Randomized Drawing
• Required exam epilogue due tonight. http://bit.ly/151-2014F-exam3epi
• Part one of the project due next Monday night.
  • Sketches due in class on Tuesday.
• Study for quiz!

Extra Credit Opportunities

Academic

• Scholars' Convocation, noon, today: Dean Latham.
• Town Hall Thursday on Sustainability, noon and 7:30 p.m. (I think)
• CS Table Friday: Shellshock

Peer Support

• Football, Saturday at noon vs. Lawrence.
• YGB, Saturday at 7:30, See, Bring, Lou, Us
• Karan's radio show 11pm Thursday nights on KDIC
• Evan's radio show 5pm Friday nights on KDIC
• Donna's radio show Sunday midnight on KDIC

Questions

How do I do other cool things with GIMP/gigls?

There's a huge list of procedures under Help -> Procedure Browser. You can call most of them, although the arguments are a bit strange in some cases.

Reading check

With your partner:

• Most important points of the reading
• Confusing issues

Most important points

Why do vectors in addition to lists?

Sometimes we want quick access to values; lists are slow, vectors are fast (by index).

Vectors let you change their contents.

Why have lists if we have vectors?

Lists can be expanded easily; vectors can't.

Lists are really easy to recurse over.

Huge number of procedures

Confusing issues

Why would you ever want vector-fill! (particularly given that we could just use make-vector)?

Mostly there to help you think about recursion over vectors.

How do we make vectors bigger?

You can't.

What's a number vector?

A vector that contains only number.

Behind the scenes: How Scheme implements vectors

Laid out in a continuous area of memory. Let's say it starts at location m. Every value takes the same amount of space, s. That means that value i is at position m+si.

Lab

• Why do we have vector-fill? answered: We can't redefine things. Hence, if we want to change them, changing in place is the way to go.
• Two approaches to vector-sum, just like there are two approaches to the normal sum. You can use direct recursion or you can use a helper.
• I like that many of you are finding a similar procedure and then just changing the appropriate parts.