Lecture4 MATLAB

8/10/2019 Lecture4 MATLAB

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Introduction to MATLAB

Dr. Ben Mertz

FSE 100Lecture 4


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Data Analysis

MATLAB is a numerical computing environment and

programming language

2-D and 3-D graphics

Numeric Computation

Algorithm Development

And more

http://www.orbisnap.com/vrtdesc.html

http://www.mathworks.com

Design, Problem Solving;

Custom GUIs;

Modeling and Analysis;

Signal and Image Processing


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Algorithm Development

Data Analysis

2-D and 3-D graphics

Numeric Computation And more

Design, Problem Solving

Custom GUIs

Modeling and Analysis Signal and Image

Processing

MATLAB is

http://www.orbisnap.com/vrtdesc.html http://www.mathworks.com

a numerical computing environment and programming language


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MATLAB also does

http://jennifertsau.com/uncategorized/matlab-fun/http://www.mathworks.com
http://jennifertsau.com/uncategorized/matlab-fun/http://jennifertsau.com/uncategorized/matlab-fun/http://jennifertsau.com/uncategorized/matlab-fun/http://jennifertsau.com/uncategorized/matlab-fun/http://jennifertsau.com/uncategorized/matlab-fun/


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Command window

with command lines

and results

Command histories

Workspace: variables

Current

Directory


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Mathematical

ComputationsExpression MATLAB Commands

Addition

3+5Subtraction 4-9Multiplication 3*2Division

9/3Square Root sqrt(4)Power 2^4

3 2

9 3

442

3 54 9


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Mathematical

Functions

ln 2

sin(2 )

cos(0)

tan( )4

Expression MATLAB Commands

Exponential exp(5)Natural Logarithm log(2)Base 10 Logarithm log10(2)Absolute Value abs(-5)Sine sin(pi)Cosine cos(2*pi)Tangent tan(pi/4)

5e

ln(2)

10log (2)

5

sin( )

cos(2 )

tan( )4


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ExamplesWrite down the mathematical expressions of

the following MATLAB commands:

5*exp(-5)+3^2/4

3+5*2-2*sqrt(9)


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ExamplesWrite down the mathematical expressions of

the following MATLAB commands:

5*exp(-5)+3^2/4

3+5*2-2*sqrt(9)

25 35

4e

3 5 2 2 9


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ExamplesWrite down the MATLAB commands of the

following mathematical expressions:

22sin 4 cos

ln(1)5 4

4


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ExamplesWrite down the MATLAB commands of the

following mathematical expressions:

2*sin(4*pi)-(cos(pi))^2

log(1)/4-5*sqrt(4)

22sin 4 cos

ln(1) 5 44


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MATLABVariables


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Variables Variables are used

as tags to which

values are assigned

Variable names

start with a letter

and are casesensitive

1

1

i

j

pi

InfNaN

Infinity

Not a number

Predefined variables:


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Define Variablesvariable name = a value (or an expression)

Examples:

a = 10A = 5*a-a^2

Variables could be defined in terms of

pre-defined variables


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Define Variablesvariable name = a value (or an expression)

Examples:

Semicolon suppresses expressions so that results will

NOT be shown in the command window.

b = 5;

c = sin(b)+log(b)-exp(b)

This_is_a_valid_name = 4^4


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ExampleCalculate the area of a circle:

What variables should be defined?

What expression(s) should be

typed in MATLAB?


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ExampleCalculate the area of a circle:

Define two variables:

Radius of the circle; Area of the circle.

Expressions in MATLAB: r=5A=pi*r^2


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Example

for and

What variable(s) should be defined?

What expression(s) should be typed in

MATLAB?

25 3 2y x x 0x2x

Calculate


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Example

for and25 3 2y x x 0x2x

Calculate

x=0

y=5*x^2-3*x+2

x=-2y=5*x^2-3*x+2

When the same

variable name is

used again, its

value is updated


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Examples in MATLAB

Vectors and Matrices


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ExampleDefine the following vector in MATLAB

2 0 2 4 6vec


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Example

vec = [-2 0 2 4 6]

vec = -2:2:6

vec = linspace(-2,6,5)

2 0 2 4 6vec


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Example

Define a vector between 0 and 20, with 50

elements

v50 = linspace(0,20,50)


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ExampleDefine the following matrix in MATLAB

40.5 sin( )

9 4

mat

mat = [pi sqrt(4); -0.5 sin(pi); 9 -4]


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MATLABImport data


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MATLAB is good for

Data Analysis

Visualization


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Import Data

Data stored in a text file could be

directly imported to MATLAB


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Example

John measured the width, depth, and length of

three objects and stored his measurements in

the file

dim.txt


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Example

dim.txt


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Example

How could John import the

measurements into MATLAB sohe could work with them?


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Import Data

.txt file that contains

only numbers

Numbers are

separated by Tab

No spaces for the file

name

Requirements of the file:


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Import Data

The .txt file could be

created using Excel Save the

excel file as type

Text (Tab Deliminated)

Requirements of the file:


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Import DataName = load('filename.txt')

Dimensions=load('dim.txt')

Dimensionsis now defined as a 3 x 3 matrix in MATLAB


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ExampleNow John wants to separate the dimensions of

the 1stobject from the rest of the data, what

would he do in MATLAB?


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Example

Object1=Dimensions(1,:)

The 1st

row of the matrix Dimensionsis nowdefined as a new vector Object1:

3.0 4.0 5.2


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MATLAB

2D Plots


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How would you plot a function y=f(x)?

What if this function is NOT well known, e.g.

2sin( ) 3 log( )

with 1 3

y x x x x

x

Question


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Create a plot of the function y=f(x)

x y=f(x)

1 3.842

1.5 7.840

2 13.125

2.5 19.330

3 26.325

2

sin( ) 3 log( ) with 1 3

y x x x x

x

y

x0 1 3


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Create 2D PlotsIn MATLAB, to create the plot of y=f(x), two

vectors, x and y, need to be defined

x y=f(x)

1 3.842

1.5 7.840

2 13.125

2.5 19.330

3 26.325

x= [1,1.5,2,2.5,3]

y= [3.841,7.840,13.125,

19.330,26.325]

x stores the xcoordinates of the points

y stores the y

coordinates of the points


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Create 2D Plots

Once the two vectors, x and y, are defined, the

command in MATLAB to create a 2D plot of

y=f(x) is

plot(x,y)


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Example

Create a plot of

sin( ),0 4y x x


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Example

Create a plot of

Use 10 points

sin( ),0 4y x x

x=linspace(0,4*pi,10)y=sin(x)

plot(x,y)

0 2 4 6 8 10 12 14-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1


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Example

Create a plot of

Use 500 points

sin( ),0 4y x x

x=linspace(0,4*pi,500)y=sin(x)

plot(x,y)

0 2 4 6 8 10 12 14-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1


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Title and Axes

x=linspace(0,4*pi,500)

y=sin(x)

plot(x,y)xlabel('x')

ylabel('sin(x)')

title('sine function')0 2 4 6 8 10 12 14

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

x

sin(x)

sine function


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Attributes of Plots

x=linspace(0,4*pi,500)

y=sin(x)

plot(x,y, 'm-')0 2 4 6 8 10 12 14

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1


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Plot Multiple Curves

Plot

and

sin( ),0 4y x x

cos( ),0 4y x x


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Step 1: Define two vectors (x and y) for

each curve:x1=linspace(0,4*pi,500)

y1=sin(x)

x2=linspace(0,4*pi,500)y2=cos(x)


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Step 2: Plot both curves and

use different attributes:

Step 3: Add legend

plot(x1,y1, 'k--', x2,y2, 'r-.')

legend('sin(x)', 'cos(x)')


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ExamplePlot the two functions for

3 3

3 5

y x

y x

0 3x

Blue dashed line

Yellow asterisk


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ExamplePlot the two

functions for:3 3

3 5

y x

y x

0 3x

Blue dashed line

Yellow asterisk

x=linspace(0,3,50)y1=3*x-3

y2=-3*x+5

plot(x,y1, 'b--',x,y2,'y*')

legend('y1', 'y2')title('Plots')

xlabel('x between 0 and 3')

ylabel('y=f(x)')


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MATLAB

Well Documented m-files

ll d fil


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Well-Documented m-file

Createa file

with a list of

commands

Savethe file

Runthe file

Header

comments

run it


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To Create an m-file,Click File -> New -> Script


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This new window will pop-up. You may type in

all the commands line by line here.

Each command occupies its own line


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% symbol will make the line a comment NOT

executable. Comments appear in green.

Commands (lines without %) appear in black.

Always include three

comment lines:

-Description of this file

-Author

-Date of creation

Comments are used as explanations. Units could

also be indicated using comments.


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When you click this RUN button, MATLAB will execute all

the commands in this file line by line.

And results will be displayed in the command window.

Semicolon

suppressesexpressions so

that results will

NOT be shown

in the command

window.


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Name Requirements Name of an m-file could contain letters,

numbers and symbols

First character must be a letter

Spaces between characters are NOT allowed


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ExampleCreate a well documented m-file to:

calculate the area of a circle with a radius of 5

inches

plot the function forsin(2 )y x 0 x

E l


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Example

Lecture4 MATLAB

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