Matlab 1: Get Started
Starting/Existing Matlab 2/2
Run matlab in command line:
In Terminal/console
i.Change to you work directory ii.Type: matlab -nodesktop
iii.To close it, type exit
Keep track of your work
●Comment your code: %
●Save your command history: diary
●Display current variables: who
●Clear variables: clear
>> diary MatlabHistory.txt; %Start to record you command history
>> a=1;
>> who;
Your variables are:
a
>> clear;
>> who;
>> diary MatlabHistory.txt; %Start to record you command history
>> a=1;
>> who;
Your variables are:
a
>> clear;
>> who;
Get Help
● Type Help, your will get a bounch of help topics. Select the topic your are looking for.
● Or you can type helpdesk to start the help window.
● Use help toolbar.
● If you know your function. Type help -Function_Name
More learning material
Get a book from library by searching keyword:
matlab
Some toturials from internet:
http://www.math.ufl.edu/help/matlab-tutorial/
http://www.cyclismo.org/tutorial/matlab/
Quick Reference:
http://www.math.umaine.edu/~hiebeler/comp/matlabR.html
http://www.cs.cmu.edu/~tom/10601_fall2012/recitations/matlab_quickref.pdf
Examples:
http://www.mathworks.se/help/matlab/examples/
Mathematical Functions
>> a=1; b=10; c=-2;
>> d = a*b + c d =8
>> d = b/c d = -5
More math funtions and predefined constant in
http://www.mathworks.se/help/matlab/functionlist.html
- Search the page by:
➔ Mathematics to find the math functions
➔ Constants and Test Matrices for predefined constant
Matlab 2: Plotting
http://www.mathworks.se/help/matlab/ref/plot.html http://www.mathworks.com/discovery/gallery.html
9
Simple Plot
Sample Code:
>> x = 0:pi/100:2*pi;
>> % x is a sequence from 0 to 2*pi, step by pi/100
>> y = sin(x);
>> sineplot = figure; %open new plot window
>> plot(x,y); % plot sin(x)
>> xlabel('x:0 : 2\pi'); ylabel('sin(x)');
>> title('Sine function'); %add labels and title
>> saveas(sineplot,'sineplot','jpg');
>> % save plot to sineplot.jpg
0 1 2 3 4 5 6 7 -1
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
x:0 : 2
sin(x)
Sine function
Multiple data sets in one plot
>> x = 0:pi/100:2*pi; y1 = sin(x); y2=2*sin(x);
>> plot(x,y1,'r-'); % plot sin(x)
>> hold
>> plot(x,y2,'g+'); % plot 2*sin(x) to the same figure
>> hold off
>> % or we can use
>> %plot(x,y1,'r-',x,y2,'g+');
>> xlabel('x:0 : 2\pi'); ylabel('sin functions');
>> title('Sin functions');
>> legend('sin(x)','2*sin(x)');% add legend
Subplots
>> x = 0:pi/100:2*pi; y1 = sin(x); y2=2*sin(x);
>> subplot(1,2,1);
>> % plot with one row, two columns
>> plot(x,y1,'r-');
>> title('sin(x)')% plot sin(x)
>> subplot(1,2,2);
>> plot(x,y2,'g+');
>> title('2*sin(x)');% plot 2*sin(x)
Matlab 3: Matrices
http://www.mathworks.se/help/matlab/learn_matlab/matrices-and-arrays.html http://www.math.utah.edu/~eyre/computing/matlab-intro/matrices.html
Construct Vectors and Matrices 1/3
●
Format
:➢ Vectors and matrices are enbraced by squares braces ([]). For example: vector1 = [1 2 3 4];
➢ Row elment separated by spaces or commas (,)
➢ Column vector separated by semicolon (;)
●
Special Matrix:
➢ Check the functions to generate special matrices, for example, eye(n) to generate identity matrix.
Construct Vectors and Matrices 2/3
Preallocate your matrix make programs run faster.
For example, you can allocate a matrix x before you use it by :
x = zeros(1, 10^6);
And then you can fill the matrix with values later.
Check for more technics to improve your program:
http://www.mathworks.se/help/matlab/matlab_prog/techniques-for-improving-performance.html
Construct Vectors and Matrices 3/3
Sample Codes:
>> vector1 = [1 2 3 4]
vector1 =
1 2 3 4
>> >> matrix1 = [1 2 3; 4 5 6; 7 8 0]
matrix1 =
1 2 3 4 5 6 7 8 0
Matrix Operation 1/3
Transpose: by adding singl quote (')
>> matrix1 matrix1 =
1 2 3 4 5 6 7 8 0
>> matrix1' ans =
1 4 7 2 5 8 3 6 0
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Matrix Operation 2/3
>> a = [1 2; 3 4];
>> b = [2 2; 2 2];
>>c= a*b c =
6 6 14 14
>> a.*b ans =
2 4
● The dimensiones of two matrices must be agree to do matrix
operation
● Matrix operation is defined by * / ^
● If you want to do
element-by-element operation, add . in front of the matrix operation.
Matrix Operation 3/3
Inverse of matrix: inv(matrix)
>> inv(a)*c ans =
2 2 2 2
>> a\c ans =
2.0000 2.0000 2.0000 2.0000
Matlab 4: Control flow
http://www.mathworks.se/help/matlab/matlab_prog/loop-control-statements.html http://www.mathworks.se/help/matlab/control-flow.html
If structure 1/2
if expression statements elseif
expression statements else
statements end
Note:
● No semicolon(;) is
needed at the end of line
● Indentation is not
needed but good for reading
● Non't forget end at last
If structure 2/2
a = rand(1);
%generate random number from uniform(0,1) if a>0.5
fprintf('a = %f is larger than 0.5',a);
elseif a==0.5
fprintf('a = %f equales 0.5',a);
else
fprintf('a = %f is less than 0.5', a);
end
for/while Loop
for index = values statements
end
while expression is true statements
end
Note:
Try to avoid loop if possible.
Matrix operation is much faster.
>> t = cputime;%start to record cpu time a = ones(10^3); b = ones(10^3,10^3);
for i = [1:1:10^3]%for loop to do a*b abi = 0;
for j = [1:1:10^3]
abi = abi + a(j)*b(i,j);
end end
Cputime-t %print cpu time to do a*b by loop ans =
3.3540
>> t = cputime; a*b; cputime-t
%print cpu time to do a*b by matrix operation ans =
Matlab 4: Functions
http://www.mathworks.se/products/
http://www.tech.plym.ac.uk/spmc/links/matlab/matlab_toolbox.html http://stommel.tamu.edu/~baum/toolboxes.html
http://www.mathworks.com/matlabcentral/newsreader/view_thread/106127
29
Define Function
Format:
function return_value = function_name( parameters ) Statement
End
Example:
Create m file as average.m (The same name as your function), put in your matlab path. Type the following content in average.m
function y = average(x) y = sum(x)/length(x);
end
Then, call the fucntion by:
>> z = 1:49;
>> average(z) ans =
Matlab Built-in Functions
Check the built-in functions. They are always more efficient.
>> help elfun % display the elementary functions
>> help specfun % display special functions
There are many free toolboxs for specific fields.
Check the following links (Please don't use them in this course if you are required to write functions by yourself.)
http://www.mathworks.se/products/
http://www.tech.plym.ac.uk/spmc/links/matlab/matlab_toolbox.html http://stommel.tamu.edu/~baum/toolboxes.html
http://www.mathworks.com/matlabcentral/newsreader/view_thread/106127
