Class 29: Simulation

Held Monday, March 12, 2001

Summary

Today we consider how to make DrScheme simulate potentially unpredictable events, like the rolling of dice or the flipping of coins.

Due

• Homework 4.

Assignments

• Lab Writeup 3.
• Read Local Procedure Bindings and Recursion.

Notes

• I spent much of the weekend working on taxes. Oh, what fun. Hence, I did not get exams graded. It looks like those of you who turned in exams late will have to wait until after break (as I said you might).
• I may be playing with the syllabus this week.
• Those of you who want to spend some of break getting ahead can check out the course at a glance and then look for the readings from last semester or from one of the other sections of the course.
  • Note that week 9 (on GIMP) is all new.
• A few of you asked for more information on let. I've started a short handout.

Overview

• The Problem of Simulation
• Scheme's random procedure
• Simulating the roll of dice
• Lab

Simulation

• At times, we write programs to model real-world situations:
  • The effect of pollutants on a lake
  • The waiting time in line at Wal-Mart
  • The playing of a card or dice game
• Each of these situations has some aspect of unpredicatability (even if we ignore the butterfly flappings of chaos theory)
• Can we write such programs in Scheme?

Random

• Scheme provides a simple procedure, random, to provide some fodder for simulations and any other times that you want to play with unpredictable behavior.
• (random n) produces an "unpredictible" number in the range [0 .. n-1].
• That's all you need to know right now.

Dice

• Here's a simple simulation problem: Simulate the roll of a single six-sided die.
  • Yes, die is the singular of dice
• Here's one possibility

  (+ 1 (random 6))
  

• See the reading for an alternative.

Lab

• Do the lab.
• Reflect?