• Continue partners!

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Preparation
• Lab
• Reflection

Preliminaries

Admin

• Office Hours:
  • Normally: 10:00-11:00 MTWF, 3:15-4:00 M (may change)
  • Currently booked: Tu 10:15-10:30, 10:45-11:00, F 10:00-11:00
  • Reserve a slot at https://rebelsky.youcanbook.me/.
  • Also feel free to try to visit during unbooked times or open times http://www.grinnell.edu/~rebelsky/schedule.html. Note that I may be busy with other things during open times.
• Next Monday, I hope to have virtual machines available for you to use on your computers. (Unless you use *nix, you can'd just download DrRacket and GIMP and hope they will interact.)

Upcoming Work

• Assignment 2.
  • Due TONIGHT at 10:30 p.m.
• Assignment 3 to be distributed tomorrow.
  • Plan: Wednesday/Friday partners will also be your HW partner.
• Lab writeup for lab 4, due Wednesday at 10:30 p.m.: Problem 2, parts def. http://bitly.com/151-2015S-lab04
• Lab writeup for lab 5, due Thursday at 10:30 p.m., Problem 4:, parts ace. http://bitly.com/151-2015S-lab05
• Readings for Wednesday: [Writing Your Own Procedures] (../readings/procedures-reading.html) and How Scheme Evaluates Expressions (Take 2)

Extra Credit Opportunities

Academic

• Friday, 12:10 p.m., JRC 224A (Day PDR), CS Table, To be determined.

Peer Support (Morning Section)

• Swimming, Friday, January 30, 6:30 p.m., Osgood Natatorium
• Swimming, Saturday, January 31, noon, Osgood Natatorium
• Julia's radio show, "The Hot Box". This week's theme is "Transportation/Leaving". Wednesday night/Thursday morning 1:00-2:00 a.m.

Recommended Events (no EC unless mentioned above)

• Women's Basketball, Tuesday, 5pm, New Darby
• Belly Dance Club, to be scheduled
• Salsa Club, Tuesdays at 7pm and Saturdays at 2pm
• Meditation group, Wednesdays at 9:00 and Sundays at 4:00 in CRSSJ
• #OneGrinnell, Wednesday, February 4 at 4:15 p.m.

Questions

You briefly mentioned this in one of the readings, but when using these procedures with inexact numbers, Scheme generates a seemingly random, large value. For instance, (denominator 2.1) generates 2251799813685248.0. Why does this happen?

They aren't random. They are just strange. Scheme represents every exact number as a sum of up to about 53 powers of two. So, 2.1 is 1x2^1 + 0x2^0 + 0x2^-1 + 0x2^-2 + 0x2^-3 + 1x2^-4 + 1x2^-5 + .... Alternately, you can think of that as 1x2 + 0x1 + 0x1/2 + 0x1/4 + 0x1/8 + 1x1/16 + 1x1/32 + 0x1/64 + 0x1/128 + .... The lcm of those denominators is 2^51, or 2251799813685248.0.

What should we know about modulo

In general, you can think of modulo as a procedure you use when you want to get a "cycle" of values. The basic cycle is 0 1 2 ... n-1 0 1 2 ... n-1 0 1 2 .... But we can add to those values to get different cycles, so you can just think of it as "cycle of length n".

Why is a unit circle diameter 1 rather than radius 1?

So that it's similar to the unit square?

Bad design on Sam's part.

Preparation

• If you haven't done so already, run /home/rebelsky/bin/csc151-setup
• After #lang racket, use (require gigls/unsafe).
• In GIMP, start the DBUS server.
• Click "Run" and cross your fingers.

Normal preparation

• Two minutes. Introduce yourself to your partner. Discuss reading. Identify: Questions and Key points

Key Points

• You can manipulate images in multiple ways: Shift, Resize, Color, Combine, and lots of other stuff to go with that.
• You can shift drawings. Doing so changes the positions of the edges of the shape, which you can see in the textual representation.

Lab

The carriage return (enter key) can be your friend

> (define sample-ellipse 
    (vshift-drawing
     1
     (hshift-drawing
      2
      (vscale-drawing
       3
       (hscale-drawing
        5
        drawing-unit-circle)))))

Reflection

• Remember: Inside-out ordering