# Lecture 2 - Matlab Introduction

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```					Lecture 2 - Matlab Introduction

CVEN 302
May 30, 2001
Lecture Goals
•   Vectors Operations
•   Matrix Operations
•   Plot & Graphics
•   Matlab files
•   Matlab controls
Vector
A vector is defined as a combination of
variables values to with components of xj ,
where j = 1,…n values.

x  x1 , x2 , x3 ,...
 x1 
x 
 
xT   2
 x3 

 
Vectors
• Matlab is designed for vector and matrix
manipulation some of the basic commands
are given as
1 
3 
 
t   ,3,4,6
1          t   
4 
6 
 
t  [1
1 
 
4     or t  [1;4;6]    t 4
6 
 
6]
Vectors
• t‟ represents the transpose of the vector “t”.
• Individual components can be represented by
t = [ 4,5,6,9], where t(3) = 6.
• [ ] represent the start and finish of the vector
and/or matrix. ( ) represent components of the
vector.
• A period “.” represent an elemental set of
functions, such as multiplication, division,etc.
Vector element Operations
•   Individual subtraction        A–B   A-B
•   Individual multiplication     A*B   A.*B
•   Individual division (left)    A/B   A./B
•   Individual division (right)   A\B   A.\B
• Individual power                AB    A.^B
Hierarchy of the vector
operations
Precedence
(1)     - Parenthesis
(2)     - Exponential from left to right
(3)     - Multiplication and division from left
to right.
(4)     - Addition and subtraction from left to
right.
Vector Operations
• Vector product - A is 1 x n vector
A * A'  1 x n * n x 1  1 x 1
A'*A  n x 1* 1 x n   n x n 

• The magnitude of the vector is a dot product
of the vector.
A * A'  1 x n * n x 1  1 x 1
A  A * A'
Vector Examples
Matrix
• A matrix is a two dimensional arrays, where
the matrix B is represented by a [ m x n ]

 b1,1  b1,n 
              
B    
bm ,1
        bm ,n 

Matrix Operations
• For addition and subtraction, the matrix
sizes must match up. If you are adding to
each component of the matrix you can do a

• Examples: [A] + [B] = [C]
[A] + 3 = [D]
Matrix Operation
• Multiplication of matrices will need to
match up the columns to the row values of
the following matrix. Scalar multiplication
will work.
• Division is different. You will either divide
member by member, where the matrices are
the same size or you will need to find the
inverse of the matrix.
Matrix Multiplication Examples
Graphical Representation
• Matlab has a function known as “plot( ),
where the values are plotted on an x-y
plane.
• General format of the graph is given as,
plot(x,y,‟symbols‟)
• The symbols represent the color, point
shape, and the line type.
Plot symbols commands
Colors             Symbols                Lines
y – yellow         . – point           - – solid line
m – mag            o – circle          : – dots
c – cyan           x – xmark           -. – line dot
r – red            + – plus            - - – dashes
g – green          * – star
b – blue           s – square
w – white          d – diamond
k – black          v – triangle down
^ – triangle up
< – left
< – right
p – pentagram
h – hexagram
Plot Commands
t = linspace(0, 2*pi);   - results in 100 data points
y1 = cos(t);             - cosine of the points
y2 = sin(t);             - sine of the points
y3 = y1.*y2;             - cos(t)*sin(t)
plot(t,y1,‟-‟) ;         - plots cosine verse t with a
straight line.
plot(t,y3,‟r:‟)          - plots cosine*sine verse t
with red dots.
Plot Commands
Example:
plot(t,y1,‟-‟,t,y2,‟g*‟,t,y3,‟r-.‟) - plots all 3
axis( [0 2*pi -1.5 1.5]) - adds axes
legend(„cos(t)‟,‟sin(t)‟,‟cos(t)*sin(t)‟) - legend

Note that the [ ] represent an array and ( ) represent a
function, and „ „ represent the symbols.
Matlab commands for
file management
The files can be written as a script, which can be
loaded into the memory. From the command line:

• “echo” - causes the file to be echoed to the screen.
• “what” - shows the type of file in the current
directory.
• “type” - will present show the file contents
Matlab Files
There are three types of files:
• Data files
– Matlab files have their own format for saving data
– ascii files are standard text files, which can be printed
out or used in excel files.
• m-files represent the program files.
• function files are functions similar to „sin(x)‟, cos(x), etc.
Data Files

Data files can be written in two forms:

• Matlab format
• ascii format
Matlab data format
MatLab generates a data   t = linspace(0, 2*pi)
file, which will have     x = cos(t)

look like:                save data1 t x
“filename”.mat            clear
what
the memory with:          data1.mat

ACSII format
An ascii file type can be    t = linspace(0 2*pi)
x = sin(t)
created by adding a flag     save data2.dat t x -ascii
on the end of the save       dir
data2.dat
command
clear
save “filename”.dat -ascii   load data2.dat -ascii
Matlab Files                      ASCII Files

The file will load the file into   The file will be loaded as an
the same format as it was          data array and will require
saved.                             you to modify to obtained the
data vectors.
Data file example
t=linspace(0,2*pi);      (data1 will have created
y1 = sin(x);              t and y1 vectors.)
save data1 t y1;
clear                    save data2.dat t y1 -ascii
clear
(created data1.mat and
will show up in home    (created a ascii file with
directory.)             the data)

Data file example continued
memory as data2 array)
whos

data2 2X100 double array

t= data2(1,:);
y1= data2(2,:);

: assigns the row to the
vector
Homework
• Check the Homework files
–   create a data file
–   input a simple program
–   run the program
–   plot the results

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