| language | contributors | |||
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Matlab |
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Matlab stands for Matrix Laboratory. It is a powerful numerical computing language commonly used in engineering and mathematics.
If you have any feedback please feel free to reach me at @the_ozzinator, or osvaldo.t.mendoza@gmail.com.
% Comments start with a percent sign.
%{ Multi line comments look
something
like
this %}
clear % Erases all your variables from memory
clc % Erases the writing on your Command Window
who % Displays all variables in memory
diary % History of session
ctrl-c % Abort current computation
help command % Displays documentation for command in Command Window
lookfor command % Searches for a given command
% Output formatting
format short % 4 decimals in a floating number
format long % 15 decimals
fprintf
% Variables & Expressions
myVariable = 4 % Notice Workspace pane shows newly created variable
myVariable = 4; % Semi colon suppresses output to the Command Window
4 + 6 % ans = 10
8 * myVariable % ans = 32
a = 2; b = 3;
c = exp(a)*sin(pi/2) % c = 7.3891
% Logicals
1 > 5 % ans = 0
10 >= 10 % ans = 1
3 ~= 4 % Not equal to -> ans = 1
3 == 3 % equal to -> ans = 1
3 > 1 && 4 > 1 % AND -> ans = 1
3 > 1 || 4 > 1 % OR -> ans = 1
~1 % NOT -> ans = 0
% Strings
a = 'MyString'
length(a) % ans = 8
a(2) % ans = y
[a,a] % ans = MyStringMyString
% Cells
a = {'one', 'two', 'three'}
a(1) % ans = 'one' - returns a cell
char(a(1)) % ans = one - returns a string
% Vectors
x = [4 32 53 7 1]
x(2) % ans = 32, indices in Matlab start 1, not 0
x(2:3) % ans = 32 53
x(2:end) % ans = 32 53 7 1
x = [4; 32; 53; 7; 1] % Column vector
x = [1:10] % x = 1 2 3 4 5 6 7 8 9 10
% Matrices
A = [1 2 3; 4 5 6; 7 8 9]
% Rows are seperated with a semi colon, each element is seperated with space or comma
% A =
% 1 2 3
% 4 5 6
% 7 8 9
A(2,3) % ans = 6, A(row, column)
A(2,3) = 42 % Update row 2 col 3 with 42
% A =
% 1 2 3
% 4 5 42
% 7 8 9
A(2:3,2:3) % Creates a new matrix from the old one
%ans =
% 5 42
% 8 9
A(:,1) % All rows in column 1
%ans =
% 1
% 4
% 7
A(1,:) % All columns in row 1
%ans =
% 1 2 3
A(:, [3 1 2]) %Rearrange the columns of original matrix
%ans =
% 3 1 2
% 42 4 5
% 9 7 8
A(1, :) =[] %Delete the first row of the matrix
size(A) % ans = 3 3
A' % Transpose the matrix
[A ; A] % Concatenation of matrices
%ans =
% 1 2 3
% 4 5 42
% 7 8 9
% 1 2 3
% 4 5 42
% 7 8 9
%Element by Element Arithmetic VS Matrix Arithmetic
A * B % Matrix multiplication
A .* B % Multiple each element in A by its corresponding element in B
%Plotting
x = 0:.10:2*pi % Creates a vector that starts at 0 and ends at 2*pi with increments of .1
y = sin(x)
plot(x,y)
xlabel('x axis')
ylabel('y axis')
title('Plot of y = sin(x)')
axis([0 2*pi -1 1]) % x range from 0 to 2*pi, y range from -1 to 1
plot(x,y1,’-’,x,y2,’--’,x,y3,’:’) % For multiple functions on one plot
% .mat files
% Save the variables in your Workspace
%M-file Scripts
%A script file is an external file that contains a sequence of statements.
%Better than typing your code in the Command Window
%Have .m extensions
%M-file Functions
%Programs that accept inputs and return an output
%Have .m extensions
% double_input.m - naming your ,m file the same as you call it in the file is required
function output = double_input(x)
%double_input(x) returns twice the value of x
output = 2*x;
end
double_input(6) % ans = 12
%User input
a = input('Enter the value: ')
%Reading in data
fopen(filename)
%Output
disp(a) % Print out the value of variable a
disp('Hello World') % Print out a string
fprintf % More control display to Command Window
%Conditional statements
if a > 15
disp('Greater than 15')
elseif a == 23
disp('a is 23')
else
disp('neither condition met')
end
%Looping
for k = 1:5
disp(k)
end
k = 0;
while (k < 5)
k = k + 1;
end
%Connecting to a MySQL Database
dbname = 'database_name';
username = 'root';
password = 'root';
driver = 'com.mysql.jdbc.Driver';
dburl = ['jdbc:mysql://localhost:8889/' dbname];
javaclasspath('mysql-connector-java-5.1.xx-bin.jar'); %xx depends on version, download available at http://dev.mysql.com/downloads/connector/j/
conn = database(dbname, username, password, driver, dburl);
sql = ['SELECT * from table_name where id = 22'] %Example sql statement
a = fetch(conn, sql) %a will contain your data
% Common math functions
sin(x)
cos(x)
tan(x)
asin(x)
acos(x)
atan(x)
exp(x)
sqrt(x)
log(x)
log10(x)
abs(x)
min(x)
max(x)
ceil(x)
floor(x)
round(x)
rem(x)
rand
randi
% Common constants
pi
NaN
inf
% Common matrix functions
zeros(m,n) % m x n matrix of 0's
ones(m,n) % m x n matrix of 1's
diag(A) % Extracts the diagonal elements of a matrix
eye(m,n) % Indentity matrix
inv(A) % Inverse of matrix A
det(A) % Determinant of A
eig(A) %Eigenvalues and eigenvectors of A
isempty(A) % Tests if array is empty
isequal(A, B) %Tests equality of two arrays
numel(A) %Number of elements in matrix
- The official website http://http://www.mathworks.com/products/matlab/