CSC151.01 2015S, Class 05: Drawings as Values ============================================= * 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 . * Also feel free to try to visit during unbooked times or open times . 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](../assignments/assignment.02.html). * 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. * Lab writeup for lab 5, due Thursday at 10:30 p.m., Problem 4:, parts ace. * Readings for Wednesday: [Writing Your Own Procedures] (../readings/procedures-reading.html) and [How Scheme Evaluates Expressions (Take 2)](../readings/scheme-eval-2.html) ### 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