# Introduction to MATLAB by dfsdf224s

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• pg 1
```									       Tutorial #1 (prepared by H.D. Ng)

Introduction to MATLAB
1.   Basic functions
2.   Vectors, matrices, and arithmetic
3.   Flow Constructs (Loops, If, etc)
4.   Create M-files
5.   Plotting
http://users.encs.concordia.ca/~hoing/course.html
To get started
• Create a directory reserved for saving files
associated with MATLAB
• After you start the MATLAB program :
To get started, type one of these: helpwin, helpdesk, or demo.
For product information, type tour or visit www.mathworks.com.

» cd c:/eddie/                   Change your current directory to the
MATLAB working directory
»
» ls
List all your files in this directory
.     ..     method1.m method2.m method3.m
All the filename
»
contained in this
MATLAB prompt
directory
Basic functions
• MATLAB as a calculator                 +      addition
» (3+5)/7        Sum of (3+5)          -      subtraction
ans =            divided by 7          /      division
*      multiplication
1.1429                               ^      power
» x = (3+5)/7     define a variable
x=
**MATLAB follows the order operation and works
1.1429        according to the following priorities:
»x               1. quantities in brackets
2. Power
x=
3. * / working from left to right
1.1429         4. + - working from left to right

** MATLAB case sensitive
Basic function (continued)
• If you want to see how many variables you have
defined so far, you can use the following command:

» who                    List all the variables in the current
MATLAB session
ans     x
List all the variables with details
»
»whos
Name        Size     Bytes Class
ans        1x1       8 double array
x          1x1       8 double array
Grand total is 2 elements using 16 bytes
Basic function (continued)
• Once you have defined some variables:
» x = -10
x=                   *Once you have define a value for a
-10                variable, you can use it to perform
algebraic operation
» y = 5*x
y=
-50
» x = (3+5)/7
x=
*By default, MATLAB displays 4
1.1429        decimal digit if the value is not an
integer
Format
• By default, the answer only displays 4 decimal
places if it is not an integer
• If you want to change the format of the output:

» format long        Other format for the output:
» pi
format short      (4 decimal places)
ans =                 format short e   (scientific notation)
3.14159265358979    format long       (more than 12)
format bank       (2 decimal place)
Special Characters
• In MATLAB, there are some special variables:

» pi               Value for π
ans =
3.1416
» i, j,
Imaginary number by default
ans =                unless you change them
0+1.0000i
ans =
0+1.0000i
Build-in function
• In MATLAB, there are also some standard build-in
functions
•Trigonometric function:
» z = sin (pi/4)            sin ( )       asin ( )
cos ( )       acos ( )
z=
tan ( )       atan ( )
0.7071
» q = log (4)
q=                  •Elementary function:
1.3863                sqrt ( )         √
exp ( )          e
log ( )          log
log10 ( )        log10
Defining a vector (Row vector)
• MATLAB is a tool for doing computations with
vectors & matrices
• Row Vectors:           Name of your vector

» v1 = [2 3, 3]        Square bracket
v1 =
2 3 3             You can use either a space or comma to
separate the elements in vector definition
» length (v1)
ans =
3         Tell you the number of elements in your
vector
Defining a vector (Row vector)
• You can perform standard linear algebra operations
on these vectors
» v2 = 3*v1             Multiplication by a scalar quantity
v2 =
6 9 9               Other vector operations:

» v3 = [2 2]            - Addition/subtraction of a vector

v3 =                    -dot product …etc

2 2
» v4 = v3+v1
??? Undefined function or variable ‘v1’
»
**Row vectors must have the same length
Defining a vector (Column vector)
• Similar you can also define a column vector
» c1 = [1;3;2]       Square bracket
c1 =
Use colon or enter the value at the
1              next line for next row elements
3
2
» c2 = [2
2
4]
c2 =
2
2
4
Defining a vector (Column vector)
• We can convert a row vector into a column vector
(or vice versa) by taking the transpose which can be
done by using a single quote ’
» v4 = c1’
Transpose operator
v4 =
1 3 2
»
Matrices
• In a similar fashion, you can define a matrix in
MATLAB by doing the following:
» a =[5 7 9
Element in first row
1 -3 -7]
a=
5 7 9                   Use a semi-colon for next row elements
1 -3 -7
» a = [ 5 7 9; 1 -3 -7]
a=
5 7 9
1 -3 -7
• Similarly, for matrix operation, it must follow the basic
rule of linear algebra, eg. dimensions must agree!
Element access
• MATLAB IS NOT ZERO INDEXED!
• x               retrieves entire matrix x
• x(1,2)          retrieves element at row 1, col 2
• x(1, 5:10)      retrieves row 1, columns 5 to 10
(use colon)
• x(1,:)          retrieves row 1, all columns
• Useful functions:
size(x)     rows, cols of x
Other build-in functions
• In MATLAB, there are also some standard build-in
functions to perform some linear algebra

•Linear algebra
diag( )    find diagonal of a square matrix
eig( )     find the eigenvalue
inv( )     find the inverse
…etc
Some housekeeping commands
• The command save can store all the variables
defined in the workspace in a binary file
matlab.mat (default name)

• You can also store individual variable by writing:
save filename X Y Z
You specify a filename

• The command load can restore the workspace from
the file matlab.mat
• The command clear all remove all variables in the
current workspace
Making a M-file
• Filename has an extension .m
• You can use M-file to do 2 things:
- script file (when you want to do many
MATLAB operations at the same
time, consisting of a sequence of
normal MATLAB statement)
- function file (to create a function)

• To create a M-file, go to the toolbar of the
MATLAB command window and from:
file new M-file
Script file               Output
%filename= method1.m              Comment (is not
clear all                         a MATLAB            » method1
x1= (2+4)/5;         Erase all    statement)          y1 =
x2= x1*7;            previously
y1= sqrt(15)                                            3.8730
defined variables
y2= exp(5)                                            y2 =
v1 = [x1 x2]                MATLAB statement           148.4132
c1 = [y1;y2];
dot_product = v1*c1           To inhibit echo         v1 =
display('SAY HI!!!!')         (operation not shown)     1.2000     8.4000
dot_product =
The filename is called method1.m
Use the command ls to check if this file is in        1.2513e+003
your currently working directory                     ans =
SAY HI!!!!
Function file
output
Indicate that this file is a function M-file
» v = [ 67 89 52 98 30]
Return value Name of your function *
v=
Input argument
function [out] = mean (x)                        67    89     52   98    30
% To calculate the mean or average of          » avg = mean(v)
% a list of number
% X is an array of number                      m=
m = length(x)                                    5
out = sum(x)/m
mean =
67.2000
*The name of your
function should be the                        avg =
name                                           67.2000
Flow Constructs
• As you learned from programming, there are times
when you want your code to make a decision:

• IF block               Conditions
if (<condition>)          <     less than
<body>            <=    less and equal then
elseif                    ==    equal
<body>            >     greater than
end
<     greater and equal then
~=    not equal
If statement
% filename method2.m             Output
else                             88
display('pass')            » method2
end
end                          ans =
# of “if” must be    »
consistent with #
of “end”
Flow Constructs
Initial value
• For loop
Final value (where you stop the loop)
for i = 1:10
<body>
end

Initial value
• For loop
Final value (where you stop the loop)
for i = 1:2:10
<body>
end                      Specify the increment
Flow Constructs
• While loop         condition
n=0
while (n <8)
n=n+1
end
Plotting
9

» x=[4 8 11]                            8.5
Plot the data        8
x=                  point and           7.5

4   8     11   connected them       7

by straight line    6.5

» y=[4 5 9]                              6

5.5

y=                  Plot the discrete    5

4   5     9    data point          4.5

4

» plot (x,y)        indicated by o            4   5   6   7   8   9   10   11

» plot(x,y,’o’)
» axis([0 10 0 10])              Change axis [xmin xmax ymin ymax]
» title(‘experimental data’)
» xlabel(‘x’)                         Labeling
» ylabel(‘y’)
» grid on                 Turn on the gird on the graph
Plotting (continued)
»z                  If the data is stored
in a matrix
z=
4     4
8     5
11    9
» plot (z(:,1),z(:,2))

All row             All row elements
elements in         in second
first column        column
Multiple plot on the same
» plot (x1, y1, x2, y2, x3, y3 )
graph (3 set of data points)
Plotting (continued)
To make a graph of y = sin(t) on the interval t = 0 to t = 10

» t = 0:.3:10;
» y = sin(t);
» plot(t,y,’r’) ;

We can also use the
commant fplot:
» fplot (‘ff’, [ 0 10])

Limit for x value
Function defined by a m-file
(make sure you put the quotation)

```
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