>> pathname = 'C:\Users\Aya\Desktop\pic';

>> for i = 1:10

imagename = strcat(pathname,int2str(i),'.jpg');

I = imread(imagename);

M(i) = mean(mean(mean(I)));% RGB image

end

>> save 'C:\Users\Aya\Desktop\MEANS.mat' M;

>> MR=load ('C:\Users\Aya\Desktop\MEANS.mat')

MR =

M: [93.6082 93.6082 93.6082 93.6082 93.6082]

2

Matlab plotting

› 2D plots

› 3D plots

M-Files

› Scripts

› User defined functions

3

Matlab has a lot of function for plotting data.

The basic one will plot one vector vs. another. The first one will be treated as the abscissa (or x) vector and the second as the ordinate (or y) vector.

The vectors have to be the same length.

>> plot (time, dist) % plotting versus time

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Matlab will also plot a vector vs. its own

index. The index will be treated as the

abscissa vector.

Given a vector “time” and a vector

“dist” we could say:

>> plot (dist) % plotting versus index

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Example:

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Example:

7

Example:

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Note: plot(g,h) g and h must have same

length, direction

Customize plot by editing in Figure Window

› Point and click edit mode with toolbar back

arrow

Change axis property

Change line style and color

Change background color

Add axis labels and title

Insert legend and text

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There are commands in Matlab to

"annotate" a plot to put on axis labels,

titles, and legends.

To put a label on the axes we would use:

› >> xlabel ('X-axis label')

› >> ylabel ('Y-axis label')

To put a title on the plot, we would use:

› >> title ('Title of my plot')

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Make a 3-D line plot

› Create 3 same-length vectors, e.g.,

>> p = [0:0.1:10]; % range vector

>> q = p./2; % same length range vector

>> r = sin(p).*cos(q); % function vector

› Plot the 3-D curve –

Example: >> plot3(p,q,r)

› Rotate the curve in 3-D using toolbar icon

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Make a 3-D surface plot

› Create a matrix of function values

Example: >> S = ((sin(p))') * (cos(q));

› Plot a surface of matrix values

>> surf(S) % polygonal facets

>> mesh(S) % wire mesh

› Rotate the plot in 3-D using toolbar icon

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Example:

Supposed we want to visualize a function

Z = 10e(–0.4a) sin (2ft) for f = 2

when a and t are varied from 0.1 to 7 and 0.1 to 2, respectively

>>> [t,a] = meshgrid(0.1:.01:2, 0.1:0.5:7);

>>> f=2;

>>> Z = 10.*exp(-a.*0.4).*sin(2*pi.*t.*f);

>>> surf(Z);

>>> figure(2);

>>> mesh(Z);

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Example:

>>> [x,y] = meshgrid(-

3:.1:3,-3:.1:3);

>>> z = 3*(1-x).^2.*exp(-

(x.^2) - (y+1).^2) ...

- 10*(x/5 - x.^3 -

y.^5).*exp(-x.^2-y.^2) ...

- 1/3*exp(-(x+1).^2 - y.^2);

>>> surf(z);

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Graph Functions (summary) Plot linear plot

stem discrete plot

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grid add grid lines

xlabel add X-axis label

ylabel add Y-axis label

title add graph title

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subplot divide figure window

figure create new figure window

pause wait for user response

hold on allows multiple plots on same axes

clf clears the figure window

axis([xmin,xmax,ymin,ymax]) controls axis properties

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Plotting Styles:

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Example: › plot(x,y,’r’) is a red line

› plot(x,y,’o’) plots circles rather than lines

› plot(x,y,’yp’) plots yellow pentagrams

Specialized 1D graphics› bar--bar chart

› pie--pie chart

› polar--polar coordintes

› semilogy, semilogx, loglog—plotting with log-scales

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Drawing a bar graph

>> clear, close all

>> clc

>> x = 0:pi/36:2*pi

>> y = cos(x)

>> bar(x,y,'b')

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Drawing a stair-stop plot

>> clear, close all

>> clc

>> x = -10:0.5:10

>> y = x.^2 + 2.*x + 2

>> stairs(x,y,'b')

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Elements of Matlab as a programming

language:

› Expressions: Arithmetic, logical, etc.

› Flow Control blocks: Conditional and Iterations

› Scripts

› Functions

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When problems become complicated and require re–evaluation, entering command at MATLAB prompt is not practical

M-files are text files containing Matlab programs. Can be called form the command line or from other M-files

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M-files: Scripts

Without input

arguments,

they do not

return any

value.

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To run the M-file, type in the name of the file at the prompt e.g. >>> test1

It will be executed provided that the saved file is in the known path

Type in matlabpath to check the list of directories listed in the path

Use path editor to add the path: File --> Set path …

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M-files: Functions Function is a ‘black box’ that

communicates with workspace through input and output variables.

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M-files: Functions

With parameters and returning values

Only visible variables defined inside the function or Parameters

Usually one file for each function defined

File must be saved to a known path with filename the same as the function name and with an extension ‘.m’

Call function by its name and arguments28

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Write a script/function that converts a Roman numeral to its decimal equivalent.

You should be able to handle the following conversion table:

It will be useful to get the Roman number into your program as a string

Matrix operators in Matlab are much faster than loops. Fast

Matlab code uses * and avoids loops

Use built-in functions as they are often heavily optimized

Minimize division – x/2 takes longer than 0.5*x

Do computations outside loop

Pre-allocate arrays

for j=1:n;a(j)=<something>;end

Setting a=zeros(1,n) before the loop speeds things up

Use subfunctions

file fname.m:

function O=fname(I)

function O2=fname2(I2)31

http://www.cs.cornell.edu/Courses/cs401/2001fa

› Contains syllabus, lecture notes, examples, homework

http://www.mathworks.com/matlabcentral/

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Advanced data objects (cell-arrays and

structs)

Special tool boxes

Simulink

Graphical User Interface

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