CpE253 - Lecture 2 - Introduction to MATLAB

8/11/2019 CpE253 - Lecture 2 - Introduction to MATLAB

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Introduction to MATLABCpE251L/253Digital Signal Processing

Lecture 2


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Workspace

Contains variables You created within

Imported into MATLAB from data files or other programs

Example: Create variables A and B in the workspace.

A = magic(4);

B = rand(3,5,2); View the contents of the workspace using whos.

Variables also appear in the Workspace pane.

Workspace variables do NOTpersist after you exit MATLAB. using

save filename.mat


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Workspace

Use the clearcommand to clear all the variables from theworkspace.

Restore data from a MAT-file into the workspace using loa

load myfile.mat


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Character Strings

Uses Output commands to display text messages

Formatting commands of plots


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Character Strings

myTextand otherTextare arrays, like all MATLAB varia Each character, including a space, is an element in the array.

Data type is char(character)

You can concatenate strings with square brackets, just as yoconcatenate numeric arrays.

longText = [myText,' - ',otherText]

longText =

Hello, world - You're right


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Character Strings

The elements of the vectors are addressed by position.>> B='My name is John Barry'

B =

My name is John Barry

>>

>> B(4)

ans =

n

>> B(12)

ans =

J


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Character Strings

It is also possible to change specific elements by addressingdirectly>> B(12:21)=Will Smith'

B =

My name is Will Smith

>>


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Character Strings

Strings can also be placed in a matrix Done by typing a semicolon; (or pressing the Enter key) at

each row.

Each row must be typed as a string

Must be enclosed in single quotes

All rows must have the same number of elements Add spacesto shorter rows to match the longest row


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Character Strings

>> Info = ['Student Name:' ; 'John Smith ' ;' ; 'A+ ]

Info =

Student Name:

John Smith

Grade:A+

>>


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Character Strings

char MATLAB makes the length of all the rows equal to that of the long

Automatically adds spaces at the endof the short lines.

Enter rows are as strings separated by a comma.

>> Info=char('Student Name:','JohnSmith','Grade:','A+')

Info =

Student Name:

John Smith

Grade:

A+

>>


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Character Strings

Variables can be defined as either a number or a string madthe samedigits

>> x=536

x =

536

>> y='536'

y =

536

>>


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Character Strings

To convert numeric values to strings, use functions, such asnum2stror int2str.

f = 71;

c = (f-32)/1.8;

tempText = ['Temperature is ',num2str(c),'C']

tempText =

Temperature is 21.6667C


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Functions

MATLAB provides a large number of functions that performcomputational tasks.

Equivalent to subroutinesor methodsin other programminlanguages.

Example: Assume we have Aand B, such as

A = [1 3 5]; B = [10 6 4];


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Functions

To call a function, enclose its input arguments in parenthesemax(A);

If there are multiple input arguments, separate them with c

max(A,B);

Return output from a function by assigning it to a variable:

maxA = max(A); When there are multiple output arguments, enclose them in

brackets:

[maxA,location] = max(A);


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Functions

Enclose any character string inputs in single quotes:disp('hello world');

To call a function that does not require any inputs and does return any outputs, type only the function name:

clc

Note: clcfunction clears the Command Window.


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Plots

Line Plots To create 2D line plots, use the plotfunction.

Example:

X = [1 2 3 5 7 7.5 8 10];

Y = [2 6.5 7 7 5.5 4 6 8];

plot(X,Y)


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Plots

Line Plots Example 2

Sine function from 0 to 2.

x = 0:pi/100:2*pi;

y = sin(x);

plot(x,y)


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Plots

Adding labels

Use the commandsxlabel, ylabel, and titleto add the necaptions/labels.

xlabel('x')

ylabel('sin(x)')

title('Plot of the Sine Function')


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Plots

You specify the color and style of the line and the color andmarkers.

plot(x,y,linespecifiers,PropertyName,PropertyValue)

Line specifiers - specifiers that define the type and color of the linmarkers.

Property Name & Property Value - can be used to specify the line a markers size and edge, and fill colors.


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Plots

Line Specifiers (Line Styles and Color)


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Plots

Line Specifiers (Marker Type)


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Plots

Examples

plot(x,y,r)

plot(x,y,--y)

plot(x,y,*)

plot(x,y,g:d)


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Plots

Property Name and PropertyValue

Specifies the thickness of theline, the size of the marker, andthe colors of the markers edgeline and fill.

Try:

plot(x,y,'--r*','linewidth',2,'markersize',12


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Plots

By adding a third input argument to the plotfunction, youthe same variables using a red dashed line.

plot(x,y,'r--')

The 'r--' string is a line specification.

Specification can include characters for the line color, style, and m


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Plots

Plots a function with the form y = f(x).fplot(function,limits,linespecifiers)

Function - function to be plotted

Limits - domain of x and, optionally, the limits of the y axis

Line specifiersalready discussed earlier


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Plots

Example:

Plot of the function for y = x2+ 4sin(2x)1 for -3 x 3

>> fplot('x^2+4*sin(2*x)-1',[-3 3])


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Plots

Two or more graphs can be created in the same plot

Type pairs of vectors inside the plotcommand

plot(x,y,u,v,t,h)

Creates three graphsy vs. x, v vs. u, and h vs. t in the same plot

Vectors of each pair must be of the same length

MATLAB automatically plots the graphs in different colors

It is also possible to add line specifiers following each pair plot(x,y,-b,u,v,--r,t,h,g:)


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Plots

Plot the following functions given the limits -2 x 2 (with elements of x having a distance of 0.01) in the same plot

y1= x2 + 3

y2= 4x + 5

y3= 10 sin(x)


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Plots

By default, MATLAB clears the figure each time you call a plottin

Reset the axes and other elements to prepare the new plot.

To add plots to an existing figure, use hold. Add the following cprevious one.

hold on

y2 = cos(x);

plot(x,y2,'r:')

legend('sin','cos')

All plots appear in the current figure window until you use holclose the window.


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Plots

linecommand

Add graphs to a plot that already exists

line(x,y,PropertyName,PropertyValue)

Do Slide 29 using the linecommand.


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Plots with Special Graphics

Vertical Bar plots

yr=[1988:1994];

sle=[8 12 20 22 18 24 27];

bar(yr,sle,'r')

xlabel('Year')

ylabel('Sales (Millions)')


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Horizontal Bar Plot

yr=[1988:1994];

sle=[8 12 20 22 18 24 27];

barh(yr,sle)

xlabel('Sales (Millions)')

ylabel('Year')


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Stairs Plot

yr=[1988:1994];

sle=[8 12 20 22 18 24 27];

stairs(yr,sle)


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Stem Plot

yr=[1988:1994];

sle=[8 12 20 22 18 24 27];

stem(yr,sle)


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Pie Plot

grd=[11 18 26 9 5];

pie(grd)

title('Class Grades')


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Histograms

Shows the distribution of data

Shows how many data points are in each bin

Width of each bar is equal to the range of the corresponding bin

Height of the bar corresponds to the number of data points in the

hist(y) y - vector with the data points

MATLAB divides the range of the data points into 10 equally spacesubranges.


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Histograms

>> y=[58 73 73 53 50 48 56 73 73 66 69 63 74 893 89 91 80 59 69 56 64 63 66 64 74 63 69];

>> hist(y)

Smallest value in the data set is 48 and the largest is 93

Range is 45 and the width of each bin is 4.5

Range of the first bin is from 48 to 52.5 and contains two points

Range of the second bin is from 52.5 to 57 and contains three points

Two of the bins (75 to 79.5 and 84 to 88.5) do not contain any points


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Histograms Number of bins can be definedhist(y,nbins)

hist(y,x)

nbins - scalarthat defines the number of bins

x - vectorthat specifies the location of the center of each bin

>> hist(y,3)

>> x=[45:10:95]

x =

45 55 65 75 85 95

>> hist(y,x)


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Histograms

You can also output the center of the bins.

[n xout]=hist(y)

[n xout]=hist(y,nbins)


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Multiple Plots On The Same Page

Multiple plots can be created on the same page with the su

command subplot(m,n,p)

Creates mx nrectangular subplots.


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Multiple Figure Windows

>> fplot('x*cos(x)',[0,10])

>> figure>> fplot('exp(-0.2*x)*cos(x)',[0,10])

Additional commands

closecloses the active Figure Window.

close(n)closes the nth Figure Window. close all closes all Figure Windows that are open.


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3-D Plots

Three-dimensional plots typically display a surface defined b

function in two variables, z = f (x,y).

To evaluate z, first create a set of (x,y) points over the dthe function using meshgrid.

[X,Y] = meshgrid(-2:.2:2);

Z = X .* exp(-X.^2 - Y.^2);

Then, create a surface plot.surf(X,Y,Z)


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3-D Plots

surfdisplays both the connecting lines and the faces of th

in color.

meshproduces wireframe surfaces that color only the linesconnecting the defining points.


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Subplots

Display multiple plots in different subregions of the same w

using the subplotfunction.

Create four plots in a 2-by-2 grid within a figure window

t = 0:pi/10:2*pi;

[X,Y,Z] = cylinder(4*cos(t));

subplot(2,2,1); mesh(X); title('X');

subplot(2,2,2); mesh(Y); title('Y');subplot(2,2,3); mesh(Z); title('Z');

subplot(2,2,4); mesh(X,Y,Z); title('X,Y,Z');


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Subplots

subplot(2,2,4)

First two inputs to the subplotfunction indicate the number of each row and column.

Third input specifies which plot is active.

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CpE253 - Lecture 2 - Introduction to MATLAB