CSE123
Introduction to Computing
Lecture 2
Introduction to MATLAB
MATLAB
• Matlab provides a technical computing
environment designed to support the
implementation of computational tasks.
• Matlab is an interactive computing
environment that enables numerical
computation and data visualization.
MATLAB
• Matlab is an effective tool.
–
–
–
–
very simple numerical or statistical calculations,
some complex statistics,
solve simultaneous equations,
make a graph, or run and entire simulation program,
• Matlab can solve
– problems in applied mathematics, physics, chemistry,
engineering, finance – almost any application area
that deals with complex numerical calculations.
MATLAB
Running MATLAB
• Double-click on the Matlab icon or select
Matlab from Start/Programs
MATLAB Windows
–
–
–
–
Command Window
Workspace
Current Directory
Command History
Numbers
Matlab represents numbers in two form, fixed point and
floating point.
Fixed point: Decimal form, with an optional decimal point.
For example:
2.6349 -381 0.00023
Floating point: Scientific notation, representing m x 10e
For example: 2.6349 x 105 is represented as 2.6349e5
The number has two parts:
• mantissa m: fixed point number (signed or unsigned), with
an optional decimal point (2.6349 in the example above)
• exponent e: an integer exponent (signed or unsigned) (5
in the example).
•Mantissa and exponent must be separated by the letter e
(or E).
Operators
“>>” is supplied by Matlab, indicates beginning of the
command.
ans = following the completion of the command with the
Enter key marks the beginning of the answer.
Operators
Try following operations:
>>
>>
>>
>>
>>
>>
3 + 5 + 2
4*22 + 6*48 + 2*82
4 * 4 * 4
4^3
56/8
8\56
Precedence of operations
(order of evaluation)
There are rules about the order of operations
1. Parentheses, innermost first
2. Exponentiation (^), left to right
3. Multiplication (*) and division (/ or \) with equal
precedence, left to right
4. Addition (+) and subtraction (−) with equal precedence,
left to right
When operators in an expression have the same
precedence the operations are carried out from left
to right. Thus 3 / 4 * 5 is evaluated as ( 3 / 4 ) * 5 and not
as 3 / ( 4 * 5 ) .
Precedence of operations
(order of evaluation)
Examples:
a
2ab
 c 3  bd 2  2
b
b  4ac
(b  c 2 ).3 f
a
e f
d
3a
3
a / b  c  (3 / 2)  b * d  2  (2 * a * b) /(b  2  4 * a * c)
a  ((( b  c ^ 2) * 3 * f ^3)...
/( d  (e  f ) /( 3 * a )))
Some built-in functions
Function
Symbol
Example
Function
Symbol
Example
Sinus
sin()
sin(pi)
Eksponential,
exp()
exp(2)
log()
log(10)
Logarithm based
10,
log1010
log10()
log10(10)
sqrt()
sqrt(25)
acos(0)
Square root,
x
atan(1)
Absolute,
|x|
abs()
abs(x)
Modulus
Remainder of x/y
rem(x,y) rem(7,2)
(=1)
ex
Cosinus
cos()
cos(pi)
Natural Logarithm
ln(x)
Tangent
tan()
tan(pi)
inv sinus
asin()
asin(0)
inv cosinus
inv tangent
acos()
atan()
Variables and Assignment Statements
Assignment statement:
variable = number
variable = expression
variable = input(‘enter a number’)
Variable names
• Must start with a letter
• May consist only of the letters a-z, digits 0-9, and
the underscore character (_)
• May be as long as you would like, but Matlab only
recognizes the first 63 characters
• case sensitive: items, Items, itEms, and ITEMS are
all different variable names.
Variables and Assignment Statements
Example:
>> mterm = 60
>> final=80;
>> quiz=60
>> grade = 0.5*midterm+0.1*quiz+0.4*final
• Variables: mterm,final,quiz,grade
• Results displayed and stored by variable name
• Semicolon at the end of a line (as in the line >>
fianl=80;) tells Matlab to evaluate the line but not to
display the results
Variables and Assignment Statements
Examples more…
>> x=5;
>> y=x+5;
>> x=2;
y is still 10 not 7 you have to run >> y=x+5 again to obtain
new value of y.
>> z=z+2 is a correct assignment in MATLAB.
If you have not supplied a value for xx, Matlab will return a
syntax error:
>> y=xx+5
??? Undefined function or variable ’xx’.
Variables and Assignment Statements
Examples more…
TC=5/9*(TF-32)
Sometimes writing an equation in multiple statements makes the equation
more understandable
numerator
=
denominator =
H
=
s^2 + 4*s + 13;
s^3 - 2*s^2 + 4*s + 5;
numerator/denominator;
Example - Solving for quadratic roots
2s2 + 10s + 12 = 0
find roots of the quadratic equation.
>>
>>
>>
>>
>>
>>
a =2;
b =10;
c =12;
disc = b^2-4*a*c;
x1 = (-b + sqrt(disc)) /(2*a)
x2 = (-b - sqrt(disc)) /(2*a)
x1 =
-2
x2 =
-3
input()
INPUT Prompt for user input.
X=input(‘enter a number’)
enter a number2
X =
2
Enter character strings as follows
Name=input(‘enter your name
enter your name
Name =
ali
:ali
:’,‘s’)
disp()
DISP
There are two general forms of the command disp.
1. disp(variable): Displays value of variable without
displaying the variable name.
2. disp(string): Displays string by stripping off the single quotes
and echoing the characters between the quotes.
String: A group of keyboard characters enclosed in single
quote marks (’). The quote marks indicate that the
enclosed characters are to represent ASCII text.
>> temp=78;
>> disp(temp); disp(’degrees F’)
78
degrees F
Display Options
• There are several commands that can be used
to display variables with more control over the
form of the display.
Commands involving variables:
who: lists the names of defined variables
whos: lists the names and sizes of defined variables
clear: clears all variables, resets default values of
special variables
clear var: clears variable var
clc: clears the command window, homes the
cursor (moves the prompt to the top line), but does
not affect variables.
clf: clears the current figure and thus clears the
graph window.
Use commands….
Computational Limitations
In Matlab, numbers are typically represented in a
floating-point representation conforming to a standard
established by the IEEE in 1985.
In the IEEE double-precision standard used by Matlab,
there are 53 bits (approx. 15 significant digits )in the
mantissa and 11 bits in the exponent (m x 2e), for a
total of 64 bits to represent a scalar number. This
provides a range of values extending from 10−308 to
10308.
Computational Limitations
Two Matlab functions, realmax and realmin, display the
largest and the smallest numbers, respectively.
>> realmax
ans =
1.7977e+308
>> realmin
ans =
2.2251e-308
Command reuse and editing
•
•
•
•
Press the up arrow cursor key (↑) to scrolls backward
through previous commands. Press Enter to execute
the selected command.
The down arrow cursor key (↓) scrolls forward
through commands
The left (←) and right arrow (→) cursor keys move
within a command at the Matlab prompt, allowing the
command to be edited.
The mouse can also be used to reposition the
command cursor, by positioning the mouse cursor
and pressing the left mouse button.
Command reuse and editing
•
•
•
•
Other standard editing keys, such as delete Del ,
backspace BkSp , home Home , and end End ,
perform their commonly assigned tasks.
Once a scrolled or edited command is acceptable,
pressing Enter with the cursor anywhere in the
command tells Matlab to process it.
Escape key Esc erases the current command at the
prompt.
Windows copy and paste operations can be used
Getting Help
•
•
•
•
•
•
•
•
help – On-line help, display text at command line help, by
itself, lists all help topics
help topic provides help for the specified topic
help command provides help for the specified command
help help provides information on use of the help command
helpwin – On-line help, separate window for navigation.
helpdesk – Comprehensive hypertext documentation and
troubleshooting
help ops: help about operators and special characters
F1 + topic and help tab from File menu.
Interrupting and Terminating Matlab
• Ctrl+C : Interrupts (aborts) processing, but does not
terminate Matlab.
• quit: Terminates Matlab
• exit: Terminates Matlab
• Select Exit under File menu: Terminates
Matlab
Files and File Management
Matlab provides a group of commands to manage user files
• pwd: Print working directory – displays the full path of the
present working directory.
• cd path: Change to directory (folder) given by path, which
can be either a relative or absolute path.
• dir : Display the names of the directories (folders) and files
in the present working directory.
• what: Display the names of the M-files and MAT-files in the
current directory.
• delete file: Delete file from current directory
• type file: Display contents of file (text file only, such as an
M-file).
Saving and Restoring Matlab Information
It is good engineering practice to keep records of calculations.
These records can be used for several purposes, including:
To revise the calculations at a later time.
To prepare a report on the project.
Diary Command
The diary commands allows you to record all of the input and displayed
output from a Matlab interactive workspace session. The commands
include:
• diary file: Saves all text from the Matlab session, except for the
prompts (>>), as text in file, written to the present working directory. If
file is not specified, the information is written to the file named diary.
• diary off: Suspends diary operation.
• diary on: Turns diary operation back on.
• diary: Toggles diary state
Saving and Restoring Matlab Information
Example:
>> diary roots
>> a=1;
>> b=5;
>> c=6;
>> x = -b/(2*a);
>> y = sqrt(b^2-4*a*c)/(2*a);
>> s1 = x+y
s1 =
-2
>> s2 = x-y
s2 =
-3
The file roots is written in your current working directory. It
can be displayed by Matlab command type roots.
Storing and Loading Workspace Values
save : Stores workspace values (variable names,
sizes, and values), in the binary file matlab.mat in the
present working directory
save data :Stores all workspace values in the file
data.mat
save data_1 x y :Stores only the variables x and
y in the file data_1.mat
load data_1 :Loads the values of the workspace
values previously stored in the file data_1.mat
Script M-Files
•Group of Matlab commands placed in a text file with
a text editor.
•Matlab can open and execute the commands exactly
as if they were entered at the Matlab prompt.
•The term “script” indicates that Matlab reads from the
“script” found in the file. Also called “M-files,” as the
filenames must end with the extension ‘.m’, e.g.
example1.m.
Script M-Files
Example : Create the file named
qroots.m in your present working
directory using a text editor:
%qroots:Quadratic
root
finding
script
format
compact;
a=1;
b=5;
c=6;
x = -b/(2*a);
y=sqrt(b^2-4*a*c)/(2*a);
s1 = x+y
s2 = x-y
To execute the script M-file,
simply type the name of the
script file qroots at the
Matlab prompt:
>> qroots
a =
1
b =
5
c =
43
6
s1 =
-2
s2 =
-3
Effective Use of Script Files
1. The name must begin with a letter and may include
digits and the underscore character.
2. Do not give a script file the same name as a variable it
computes
3. Do not give a script file the same name as a Matlab
command or function.
To check existence of command, type
exist(’rqroot’). This command returns one of the
following values:
0 if rqroot does not exist
1 if rqroot is a variable in the workspace
2 if rqroot is an M-file or a file of unknown type in
the Matlab search path
….
Effective Use of Script Files
4. As in interactive mode, all variables created by a script
file are defined as variables in the workspace. After script
execution, you can type who or whos to display
information about the names, data types and sizes of
these variables.
5. You can use the type command to display an M-file
without opening it with a text editor.
For example, to view the file rqroot.m, the command is
type rqroot.
Matlab Search Path, Path Management
Matlab search path: Ordered list of directories that
Matlab searches to find script and function M-files
stored on disk.
Commands to manage this search path:
matlabpath: Display search path.
addpath dir: Add directory dir to beginning of
matlabpath. If you create a directory to store your
script and function M-files, you will want to add this
directory to the search path.
rmpath dir: Remove directory dir from the
matlabpath.