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September 30, 2008 Lecture 10 2
Previous lecture
User-defined functions
Today’s lecture
User-defined functions Examples local memory space
Announcements:
Section in classrooms this week We return Prelim 1 at the end of lecture. If you don’t get your paper in lecture, pick it up during consulting hours at ACCEL Green Rm (Engineering Lib., Carpenter Hall) starting at 4pm today.
Accessing your functions
For now*, put your related functions and scripts in the same directory.
dotsInCircles.m
randDouble.m
polar2xy.m
drawColorDot.m
*The path function gives greater flexibility. Not required in CS1112.
MyDirectory
Any script/function that calls polar2xy.m
September 30, 2008 Lecture 10 4
dotsInCircles.m
(functions with multiple input parameters) (functions with a single output parameter) (functions with multiple output parameters) (functions with no output parameter)
September 30, 2008 Lecture 10 5
Why write user-defined function?
- Elevate reasoning by hiding details
- Facilitate top-down design
- Software management
- A function can be independently tested easily
- Keep a driver program clean by keeping detail code in functions—separate, non-interacting files
September 30, 2008 Lecture 10 6
Script vs. Function
A script is executed line-by- line just as if you are typing it into the Command Window The value of a variable in a script is stored in the Command Window Workspace
A function has its own private (local) function workspace that does not interact with the workspace of other functions or the Command Window workspace Variables are not shared between workspaces even if they have the same name
September 30, 2008 Lecture 10 7
What will be printed?
% Script file
p= -3;
q= absolute(p);
disp(p)
function q = absolute(p)
% q is the absolute value of p
if (p<0)
p= -p;
end
q= p;
A: -3 B: 3 C: error
September 30, 2008 Lecture 10 9
What will be printed?
% Script file p= -3; q= absolute(p); disp(p)
function q = absolute(p) % q is the absolute value of p if (p<0) p= -p; end q= p; Command Window Workspace p -
September 30, 2008 Lecture 10 12
What will be printed?
% Script file p= -3; q= absolute(p); disp(p)
function q = absolute(p) % q is the absolute value of p if (p<0) p= -p; end q= p; Command Window Workspace p -
Function absolute’s Workspace p (^) -
September 30, 2008 Lecture 10 14
What will be printed?
% Script file p= -3; q= absolute(p); disp(p)
function q = absolute(p) % q is the absolute value of p if (p<0) p= -p; end q= p; Command Window Workspace p -
Function absolute’s Workspace p (^) -
September 30, 2008 Lecture 10 15
What will be printed?
% Script file p= -3; q= absolute(p); disp(p)
function q = absolute(p) % q is the absolute value of p if (p<0) p= -p; end q= p; Command Window Workspace p -
Function absolute’s Workspace p (^3)
September 30, 2008 Lecture 10 16
What will be printed?
% Script file p= -3; q= absolute(p); disp(p)
function q = absolute(p) % q is the absolute value of p if (p<0) p= -p; end q= p;
Command Window Workspace p -
Function absolute’s Workspace p (^3) q 3
September 30, 2008 Lecture 10 17
What will be printed?
% Script file p= -3; q= absolute(p); disp(p)
function q = absolute(p) % q is the absolute value of p if (p<0) p= -p; end q= p;
Command Window Workspace p -
Function absolute’s Workspace p (^3) q 3
September 30, 2008 Lecture 10 25
x = 1;
y = 3;
x = f(x,y);
y = x;
disp(y)
function y = f(y,x)
x = x+1;
y = x+1;
What is the output?
A: 3 B: 4 C: 5 D: 6 E: 7
September 30, 2008 Lecture 10 26
Subfunction
There can be more than one function in an M-file
top function is the main function and has the name of
the file
remaining functions are subfunctions, accessible only by
the functions in the same m-file
Each (sub)function in the file begins with a function
header
Keyword end is not necessary at the end of a
(sub)function
September 30, 2008 Lecture 10 28
Array index starts at 1
Let k be the index of vector x, then k must be a positive integer 1<= k <= length(x) To access the k th^ element: x(k)
x 5 .4 .91 -4 -1 7 1 2 3 4 5 6
September 30, 2008 Lecture 10 30
Prelim 1
Q1: program trace; boolean expression ☺ Q2: common loop patterns ☺ Q3: conditional ☺. Q4: while-loop; simulation ☺ Q5: nested for-loops ☺/
Median 90
Mean 86.4; Standard Deviation 12.
