1. Introduction to MATLAB
Iran University of Science and Technology, Computer Engineering Department,
Introduction to MATLAB
Ehsan Adeli M.

2. Outline Introduction MATLAB Environment Getting Help
Vectors, Matrices, and Linear Algebra
Plotting
User Defined Functions
Image Manipulation and Processing
Audio Processing
Filters and Operations
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3. Introduction MATLAB Stands for MATrix LABoratory.
The MATLAB environment allows the user to:
manage variables
import and export data
perform calculations
generate plots
develop and manage files for use with MATLAB.
A script can be made with a list of MATLAB commands like other programming language.
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4. Environment
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5. Getting Help Type one of following commands in the command window:
help – lists all the help topic
help topic – provides help for the specified topic
help command – provides help for the specified command
help help – provides information on use of the help command
helpwin – opens a separate help window for navigation
lookfor keyword – Search all M-files for keyword
Or simply press ‘F1’ and use the graphical help window.
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6. Variables Variable names: when a semi-colon
Must start with a letter
May contain only letters, digits, and the underscore “_”
Matlab is case sensitive, i.e. one & OnE are different variables.
Matlab only recognizes the first 31 characters in a variable name.
when a semi-colon
>> tutorial = 1234;
>> tutorial = 1234
”;” is placed at the end of each command, the result is not displayed.
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7. Variables (Cont’d) Special variables: Commands involving variables:
ans : default variable name for the result
pi: π = …………
eps: ∈ = e-016, smallest amount by which 2 numbers can differ.
Inf or inf : ∞, infinity
NaN or nan: not-a-number
Commands involving variables:
who: lists the names of defined variables
whos: lists the names and sizes of defined variables
clear: clears all variables, reset the default values of special variables.
clear name: clears the variable name
clc: clears the command window
clf: clears the current figure and the graph window.
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8. Vectors >> x = [ 0 0.25*pi 0.5*pi 0.75*pi pi ]
>> y = [ 0; 0 25*pi; 0 5*pi; 0 75*pi; ]
y =
0.7854 y
2.3562
3.1416
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9. Vectors (Cont’d)
Vector Addressing – A vector element is addressed in MATLAB with an integer index enclosed in parentheses.
>> x(3)
The colon notation may be used to address a block of elements (start : increment : end)
start is the starting index, increment is the amount to add to each successive index, and end is the ending index. A shortened format (start : end) may be used if increment is 1.
>> x(1:3)
ans =
NOTE: MATLAB index starts at 1.
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10. Vectors (Cont’d)
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11. Array Operations Scalar-Array Mathematics:
Element-by-Element Array-Array Mathematics:
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12. Matrices
A Matrix array is two-dimensional, having both multiple rows and multiple columns, similar to vector arrays:
It begins with [, and end with ]
spaces or commas are used to separate elements in a row
semicolon or enter is used to separate rows.
Matrix Addressing:
matrixname(row, column)
colon may be used in place of a row or column reference to select the entire row or column.
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13. Matrices (Cont’d)
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14. Matrices (Cont’d)
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15. Example, Linear Equations
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16. Plotting Plotting Curves: Multiple Curves: Multiple Figures: Subplots:
plot (x,y) – generates a linear plot of the values of x (horizontal axis) and y (vertical axis).
semilogx (x,y) – generate a plot of the values of x and y using a logarithmic scale for x and a linear scale for y
semilogy (x,y) – generate a plot of the values of x and y using a linear scale for x and a logarithmic scale for y.
loglog(x,y) – generate a plot of the values of x and y using logarithmic scales for both x and y
Multiple Curves:
plot (x, y, w, z) – multiple curves can be plotted on the same graph by using multiple arguments in a plot command. The variables x, y, w, and z are vectors. Two curves will be plotted: y vs. x, and z vs. w.
legend (‘string1’, ‘string2’,…) – used to distinguish between plots on the same graph
Multiple Figures:
figure (n) – used in creation of multiple plot windows. place this command before the plot() command, and the corresponding figure will be labeled as “Figure n”
close – closes the figure n window.
close all – closes all the figure windows.
Subplots:
subplot (m, n, p) – m by n grid of windows, with p specifying the current plot as the pth window
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17. Plotting (Cont’d)
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18. Flow Control
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19. Loops break – is used to terminate the execution of the loop.
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20. M-Files A M-file is a group of MATLAB commands.
MATLAB can open and execute the commands exactly as if they were entered at the MATLAB command window.
To run the M-files, just type the file name in the command window. (make sure the current working directory is set correctly)
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21. User Defined Functions
Add the following command in the beginning of your m- file:
function [output variables] = function_name (input variables);
Note that the file name should be the same as the function name.
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22. Images in MATLAB MATLAB can import/export several image formats
BMP (Microsoft Windows Bitmap)
GIF (Graphics Interchange Files)
HDF (Hierarchical Data Format)
JPEG (Joint Photographic Experts Group)
PCX (Paintbrush)
PNG (Portable Network Graphics)
TIFF (Tagged Image File Format)
XWD (X Window Dump)
MATLAB can also load raw-data or other types of image data
Data types in MATLAB
Double (64-bit double-precision floating point)
Single (32-bit single-precision floating point)
Int32 (32-bit signed integer)
Int16 (16-bit signed integer)
Int8 (8-bit signed integer)
Uint32 (32-bit unsigned integer)
Uint16 (16-bit unsigned integer)
Uint8 (8-bit unsigned integer)

23. Images in MATLAB
• Binary images : {0,1} • Intensity images : [0,1] or uint8, double etc. • RGB images : m-by-n-by-3 • Indexed images : m-by-3 color map • Multidimensional images m-by-n-by-p (p is the number of layers)

24. Image import and export
Read and write images in Matlab
>> I=imread('cells.jpg');
>> imshow(I)
>> size(I)
ans = (RGB image)
>> Igrey=rgb2gray(I);
>> imshow(Igrey)
>> imwrite(lgrey, 'cell_gray.tif', 'tiff')
Alternatives to imshow
>>imagesc(I)
>>imtool(I)
>>image(I)

25. Images and Matrices How to build a matrix (or image)?
>> B = zeros(3,3)
B =
>> C = ones(3,3)
C =
>>imshow(A) (imshow(A,[]) to get automatic pixel range)

26. Image format conversion
Convert between intensity/indexed/RGB to binary format:
dither()
Convert between intensity format to indexed format:
gray2ind()
Convert between indexed format to intensity format:
ind2gray()
Convert between indexed format to RGB format:
ind2rgb()
Convert a regular matrix to intensity format by scaling:
mat2gray()
Convert between RGB format to intensity format:
rgb2gray()
Convert between RGB format to indexed format:
rgb2ind()
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27. Colormaps I = imread (‘lena.bmp’); imshow (I); colormap (cool);
Autumn, bone, colorcube, cool, copper, flag, gray, hot, hsv, jet, pink, prism, spring, summer, white, winter
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28. Video mov = aviread(filename) mov = aviread(filename, index)
fileinfo = aviinfo(filename)
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29. Digital Audio
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30. Audio [road,fs]=wavread('road.wav');
The array road now contains the stereo sound data and fs is the sampling frequency. 
This data is sampled at the same rate as that on a music CD (fs=44,100 samples/second).
The left and right channel signals are the two columns of the road array:
 left=road(:,1);
right=road(:,2);
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31. time=(1/44100)*length(left); t=linspace(0,time,length(left));
plot(t,left)
xlabel('time (sec)');
ylabel('relative signal strength')
soundsc(left,fs)       % plays left channel as mono
 soundsc(right,fs)    % plays right channel mono (sound nearly the same)
 soundsc(road,fs)     % plays stereo (ahhh…)
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