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Introduction to MATLABIntroduction to MATLABThe language of Technical Computing
MATLABMATLAB
MATrix LABoratory- Everything is represented by matrices!
It is a program for doing Numerical Computation.
Also used widely as a programming language to develop tools for Machine Learning.
Why MATLAB?Why MATLAB?Large toolbox of numeric/image
library functions.Very useful for displaying, visualizing
data. High-level: focus on algorithm
structure, not on low-level details. allows quick prototype development
of algorithms.It is an Interpreter, not as fast as compiled code.
The MATLAB EnvironmentThe MATLAB Environment
VariablesVariablesMATLAB treats all variables as
matrices. For our purposes a matrix can be thought of as an array, in fact, that is how it is stored.
Vectors are special forms of matrices andcontain only one row OR one column.
Scalars are matrices with only one row AND one column.
MATLAB ProgrammingMATLAB ProgrammingThe symbol “%” is used to
indicate a Comment.A “;” at the end of the line
implies MATLAB won’t print the output of the statement. Otherwise it will print the output, which is sometimes useful for printing variable values.
MATLAB ProgrammingMATLAB Programminga = [1,2,3,4]MATLAB Output:a = 1 2 3 4
a=[1,2,3,4]; %Notice the semicolon
MATLAB Output:<Empty>
Command LineCommand LineMATLAB's command line is like a
standard shell: - Up arrow to recall commands
without retyping and down arrow to go forward.
Opening a new file in editor:>> edit test.m MATLAB source file extension is .m.Running a program : >> test
MATLAB ProgrammingMATLAB Programminga = [1 2; 3 4]; % Creates a 2x2
matrix The simplest way to create a
matrix is to list its entries in square brackets. The ";" symbol separates rows; the (optional) "," separates columns.
N = 5 % A scalar v = [1 0 0] % A row vector
MATLAB ProgrammingMATLAB Programmingv = [1; 2; 3] % A column vectorv = v’ Transpose a Vector or Matrix(row
to column and column to row)v = [] Empty Vector
MATLAB ProgrammingMATLAB Programmingm = zeros(2, 3) Creates a 2x3 matrix of zerosv = ones(1, 3) Creates a 1x3 matrix (row vector) of
onesm = eye(3) %Identity matrix (3x3)v = rand(3, 1) Randomly filled 3x1 matrix (column vector)
Indexing in MATLABIndexing in MATLAB
REMEBER: Indices always start from “1”, not “0”.
Matrix(ROW#,COLUMN#)m(1,3) %1st row 3rd columnm(2,:) %access whole second
rowm(:,3) %access whole second
column
OperatorsOperatorsAssignment = a = b (assign b to
a)Addition + a + bSubtraction - a -bMultiplication * or .* a*b or a.*bDivision / or ./ a/b or a./bPower ^ or .^ a^b or a.^bA “.” means element wise operation
Conditional StructuresConditional Structures
for i=1:2:7 %Loop from 1 to 7, steps of 2
if(i==3)disp(‘i is 3’) %print output
elseif(i==5)disp(‘i is 5’)
end end
FunctionsFunctions
All functions are separate m-files. The first line in a function file
must be of this form: function [outarg_1, ..., outarg_m] = myfunction(inarg_1, ..., inarg_n)
The function name should be the same as that of the file.
Function ExampleFunction Examplemyfunction.m
function y = myfunction(x)
a = [-2 -1 0 1]; y = a + x;
Function ExampleFunction Exampleanotherfunction.m
function [y, z] = anotherfunction(a, b)
y = a + b; z = a - b;
PlottingPlotting
x=rand(1,100);y=rand(1,100);plot(x,y,’*’);
PlottingPlottingTo put a label on X-Axisxlabel(‘my x label’);
To put a label on Y-Axisylabel(‘my y label’);
To put a Title of the Plottitle(‘my title’);
MATLAB Image ProcessingMATLAB Image ProcessingImage Processing Toolbox is
needed.I=imread(‘cute_baby.jpg’); %read
Imageimshow(I) %show image
MATLAB Image ProcessingMATLAB Image Processing
I2=rgb2gray(I); % convert RGB to gray
imwrite(I2, ‘cute.jpg’); % save gray image
figure, imshow(I2) % image in new figure
MATLAB Image ProcessingMATLAB Image Processing
figure,imhist(I2) % show histogram
MATLAB Image ProcessingMATLAB Image ProcessingFrom the histogram, we see that
the image intensity is missing low values, only high values are present.
MATLAB Image ProcessingMATLAB Image Processing
I3 = histeq(I2); %Histogram Equalization
figure, imhist(I3);
MATLAB Image ProcessingMATLAB Image Processing
figure, imshow(I2) %Original imagefigure, imshow(I3) % Equalized
Image
Help with MATLABHelp with MATLABType help at the MATLAB prompt
or help followed by a function name for help on a specific function.
Online documentation for MATLAB at the MathWorks website:
www.mathworks.comThere are also numerous tutorials
online that are easily found with a web search.
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