Homework 9

1
Homework 9
Sun., 11/3
( M T sections )

• Due

at midnight
Mon., 11/4
( W Th sections )

• Problems

http//www.cs.hmc.edu/courses/2001/fall/cs5/week_0
9/homework.html

• Tutors available

names and hours on syllabus on CS 5 home
page http//www.cs.hmc.edu/courses/2002/fall/cs5/
Fri Afternoon 1-4pm (Parsons LAC) Sat
Afternoon 1-4pm (Parsons LAC) Sun Afternoon
1-4pm (Parsons LAC Sun Evening 7-12pm
(Parsons LAC) Mon Evening 7-12pm (Parsons
LAC)
2
Problem 2 -- Life
Evolutionary rules

• Everything depends on ones eight neighbors

• Exactly 3 neighbors give birth to a new, live
  cell!

• Exactly 2 or 3 neighbors keep an existing cell
  alive

• Any other number of neighbors kill the central
  cell (or keep it dead)

white cells are empty
black cells are alive
3
Problem 2 -- Life
public void update(int last, int next)
For each generation

• 0 represents an empty cell
• 1 represents a living cell
• outermost edge should always be empty (even if
  there are 3 neighbors)
• compute all cells based on their previous
  neighbors before updating any of them

white cells are empty
black cells are alive
4
Problem 2 -- Life
// implementing the evolutionary rules
r,c
last
r,c
next
5
Problem 2 -- Life
public void update(int last, int next)
// outline of code
g.lifeUpdate(next) //draw new state!

6
Problem 2 -- Life
Details on getting and using the code...

• Download from CS 5 home page (first page, top
  link).
• Be sure to unzip resulting file.
• Using project go into NewGrid folder and open
  NewGrid.mcp project file.
• The CS5App.java file contains an empty update
  method
• You can use any colors to actually show the live
  and empty cells (default black is alive white
  is dead).
• Testing is easiest on a small (e.g. 10x10) grid.
• Click on squares to toggle their state (helpful
  in debugging).

7
Problem 1
Overall structure of main similar to HW8s
problem 1
Initial Setup
Get the number of rows and columns
Create an array of the appropriate number of
elements (doubles).
Get initial values from the user into the array.
printMenu enterArray printArray multRow addR1ToR2
addMR1ToR2 solve
Menu
Methods
(0) Change the values in the array (1) Print the
array (2) Multiply an array row (3) Add one row
to another (4) Add a multiple of one row to
another (5) Solve! (9) Quit Which choice would
you like?
8
2d arrays -- naming things
double arr
arr new doublenRowsnCols
double
double
double
double
double
double
double
double
double
double
double
double
9
Multiplying rows
Before
After
2.00 3.00 -1.00 -8.00 -3.00 -1.00
2.00 42.00 1.00 -9.00 4.00 56.00
2.00 3.00 -1.00 -8.00 -3.00 -1.00
2.00 42.00 10.00 -90.00 40.00 560.00
public static void multRow(double arr, int r,
double m)
10
Gaussian Elimination
Setup
2.00 3.00 -1.00 -8.00 -3.00
-1.00 2.00 42.00 1.00
-9.00 4.00 56.00
Will any array work?
arr
Goal

• get 1s along the diagonal

• get 0s elsewhere on the left

Algorithm
2.00 3.00 -1.00 -8.00 -3.00
-1.00 2.00 42.00 1.00
-9.00 4.00 56.00

• go column-by-column

• how many columns?
• how many rows in each column?

11
Solve
1.00 1.50 -0.50 -4.00 -3.00
-1.00 2.00 42.00 1.00
-9.00 4.00 56.00
multiply Row 0 by 0.5
1.00 1.50 -0.50 -4.00 0.00
3.50 0.50 30.00 0.00
-10.50 4.50 44.00
add 3 times Row 0 to Row 1 add -1 times Row 0 to
Row 2
repeat for column 2
and column 3
and so on...
12
Solve
public static void solve(double arr)
13
Debugging Aids
//for debugging.... public static void
userPrompt() H.out.print("enter any text to
continue...") String line H.in.nextWord()
public static void someFunction(int arr)
boolean debug true for(int i 0 i lt
arr.length i) double blah
1/arrii multRow(arr,i,blah) if(debug)
H.out.print(blah ") H.out.print(blah)
H.out.println(".........") printArra
y(arr) userPrompt() //do some more
stuff //some more stuff