1. Problem Solving with MATLAB
CPET 190
Lecture 7
Problem Solving with MATLAB
Paul Lin
February 7, 2005
Lecture 7 - By Paul Lin

2. Lecture 7: MATLAB Built-In Functions
7-1 Managing Variables and Workspace
7-2 MATLAB Commands for Working with Files and the Operating System
7-3 Controlling Command Window
7-4 Time and Date Functions
7-5 Special Variables and Constants
February 7, 2005
Lecture 7 - By Paul Lin

3. 7-1 Managing Variables and Workspace
Removing Unneeded Variables
who - List current variables
whos - List current variables, long form
clear - Clear variables and functions
Creating New Variables
length - Length of vector
size - Size of matrix
Saving to and Retrieving from Disk Files
load - Retrieve variables from disks
save - Save workspace variables to disk
pack - Consolidate workspace memory
Workspace display
disp - Display matrix or text
fprintf
February 7, 2005
Lecture 7 - By Paul Lin

4. 7-1 Managing Variables and Workspace (continue)
Example 7-1:
%cpet190_ex7_1.m
F = 4000;
T = 1/F;
dt = 0.01*T;
t = 0:dt:2*T;
e1 = 5*sin(2*pi*F*t);
len = length(e1)
size_e1 = size(e1)
e2 = zeros(size(e1));
num = rand(2);
fprintf('The random number array is %g\n', num);
fprintf('\n');
disp('The random numbers');
disp(num);
whos
save ex7_1
clear
load ex7_1
February 7, 2005
Lecture 7 - By Paul Lin

5. 7-1 Managing Variables and Workspace
Example 7-1: Output
February 7, 2005
Lecture 7 - By Paul Lin

6. 7-2 Working with Files and OS
The commands for working with files and operating system
Command Purpose
pwd Show present working directory
cd Change current working directory
dir Directory listing (Window OS)
ls Directory Listing (Unix/Linux OS)
delete Delete file
diary Save text of MATLAB session
! Execute OS commands
February 7, 2005
Lecture 7 - By Paul Lin

7. 7-2 Working with Files and OS
Example 7-2 (cont.)
>> diary
>> diary off
>> diary on
>> !time
The current time is: 11:31:05.02
Enter the new time:
Open diary file using MATLAB M-file editor, MS NOTEPAD, or MS Word
help
Example 7-2
>> pwd
ans =
C:\Courses\CPET190\matlabex190
>> cd ..
C:\Courses\CPET190
>> dir
Mlin_CPET190
Exs
Quiz Lectures
MATLABExs
February 7, 2005
Lecture 7 - By Paul Lin

8. 7-3 Controlling the Command Window
clc Clear command window
home Send cursor home (upper-left corner of command window)
format Set output format
more Control paged output in command window
echo Echo on/off commands inside script files, for debugging purposes
February 7, 2005
Lecture 7 - By Paul Lin

9. 7-4 Time and Date Functions
Function Purpose
date Calendar
clock System clock; accuracy 1/100th of a second
now Current date and time as serial date number
datestr Convert a serial date number into the common date/time, save as a string
cputime How many seconds the MATLAB session is active; accuracy 1/100 th of second
etime Elapsed time function
tic Start watch timer function
toc Stop watch timer function
February 7, 2005
Lecture 7 - By Paul Lin

10. 7-4 Time and Date Functions
Example 7-3:
>> date
ans =
03-Oct-2004
>> now
7.3222e+005
>> datestr(now)
03-Oct :47:29
>> help datestr
February 7, 2005
Lecture 7 - By Paul Lin

11. 7-4 Time and Date Functions (continue)
CLOCK Current date and time as date vector.
CLOCK returns a six element date vector containing the
current time and date in decimal form:
CLOCK = [year month day hour minute seconds]
The first five elements are integers. The seconds element
is accurate to several digits beyond the decimal point.
FIX(CLOCK) rounds to integer display format.
Example:
>> clock
ans =
1.0e+003 *
February 7, 2005
Lecture 7 - By Paul Lin

12. 7-4 Time and Date Functions (continue)
Example 7-4 measuring program execution time (accuracy – 1/100 th of a second) using cputime function
t1_1 = cputime;
for i =1:1000
num_array = inv(rand(30));
end
t1_2 = cputime;
time_1000 = t1_2 - t1_1
time_once = time_1000/1000
time_1000 =
0.3610
time_once =
3.6100e-004
February 7, 2005
Lecture 7 - By Paul Lin

13. 7-4 Time and Date Functions
Example 7-5 measuring program execution time (accuracy – 1/100 th of a second) using tic and toc functions
tic;
for i =1:1000
num_array = inv(rand(30));
end
toc
elapsed_time =
0.3610
February 7, 2005
Lecture 7 - By Paul Lin

14. 7-5 Special Variables and Constants
Example 7-6: AC circuit calculation using complex numbers.
A RLC circuit is shown on this slide, find
Total impedance Z
Voltage and current across each components
February 7, 2005
Lecture 7 - By Paul Lin

15. 7-5 Special Variables and Constants (continue)
Example 7-6:
Analysis: Domain knowledge
XL = 2πfL, where L is the inductance in Henry, f is the frequency of ac source
XC = 1/(2 πfC), where C is the capacitance in Farard
Z = R + j(XL – XC) -- total impedance, where j shows the imaginary component of a complex number
I = E/Z, total current
VR = I*R, voltage drop across resistor
VL = I*XL, voltage drop across the inductor
VC = I*XC voltage drop across the capacitor
February 7, 2005
Lecture 7 - By Paul Lin

16. 7-5 Special Variables and Constants (continue)
Example 7-6: MATLAB Program
%RLC_1.m
f = 60; R = 8;
% Peak value of the sine wave
e = 10;
XL = j*6; XC = -j*2;
Z = R + (XL+XC)
theta = angle(Z) % pi
% pi
% = ----
% theta_degree theta
theta_degree = (180*theta)/pi
% degree = pi
mag_Z = abs(Z)
February 7, 2005
Lecture 7 - By Paul Lin

17. 7-5 Special Variables and Constants (continue)
Example 7-6:
MATLAB Program (cont.)
%RLC_1.m %
I = e/Z
I_thea_degree = angle(I) * (180)/pi
I_mag = abs(I)
VR = I*R
VL = I*XL
VC = I*XC
VR + (VL + VC)% e = 10 volt
VR = i VL = i VC = i >> VR + (VL + VC) ans = 10
February 7, 2005
Lecture 7 - By Paul Lin

18. Summary Managing Variables and Workspace
MATLAB Commands for Working with Files and the Operating System
Controlling Command Windows
Date and Time Functions
Special Variables and Constants
February 7, 2005
Lecture 7 - By Paul Lin

19. Question?
Answers
February 7, 2005
Lecture 7 - By Paul Lin