Octave Cheatsheet

General Commands

PS1("custom>> ");        % For the Custom prompt

a = 3;      % The semi-colon supresses the output

help(eye)   % Gives some description about the eye function
who         % Displays all the variables in the scope
whos        % Gives the detailed display of variables

clear a     % Deletes the variable a
clc         % Clear Screen
close       % Close the given figure

save variable.mat a;    % Saves the variable a in the file
save variable.txt a -ascii;    % Saves the variable a in human readable

pause;      % Go into an infinte sleep mode, by pressing enter you can return to prompt

Basic Operations

Variables

a = 3;
b = 'hi';

Output

a  = pi;
a           % Simply give at the prompt
disp(a);    % print function in octave
disp(sprintf('Vaue of pi is: %0.2f', a))        % C style printing

Arthimetic Operations

5 + 6
5 - 4
5 * 8
1 / 2
2 ^ 6       % Exponentation

Logical Opeartions

1 == 2      % false
1 ~= 2      % not equal to
1 && 0      % AND
1 || 0      % OR
xor(1, 0)

Vectors and Matrices

Vectors

row = [1, 2, 3]     % Row vector , is a separator in a row

col = [1; 2; 3]     % Column vector ; separates the rows

length(row)         % Gives the length of vector/ length of longest dimension in matrix

In-built Functions

Mathematical

v = [0.26, 2.22, 4]
matrix = [1, 23; 30, 4; 5, 6]

log(3)              % Logrithmic
exp([1, 2])         % Exponential
abs([-1, 2, -3])    % Absolute
-v                  % similar to -1 * v

[val, ind] = max(v) % Returns an array of which has max value and it's index
max(matrix)     % Returns column-wise maximum

find([1, 0, 3, 2])      % Returns the indexes of all the non-zero elements
magic(3)        % returns a 3x3 magic square matrix

sum(matrix)     % Sum of a matrix
floor(v)
ceil(v)

Matrices

matrix = [1, 2; 3, 4; 5, 6]
eye(3)          % Diagonal matrix of order 3
ones(2, 3)      % [1, 1, 1; 1, 1, 1]
zeros(1, 3)     % [0, 0, 0]
mat = rand(3, 2)    % A random 3x2 matrix
randn(1, 100)   % Random matrix following a normal distribution

size(matrix)    % Gives the dimensions of the matrix as a matrix[row, column] size(<matrix>, [axis])

matrix(3, 2)    % A usual matrix indexing
matrix(:,2)     % : means all the elements in the corrsponding row/column.
matrix([1 3],:) % Everything from the 1st and 3rd row

matrix = [matrix, [7; 8; 9]]   % Appending a row to the matrix(right side)
matrix(:, 3) = [10; 11; 12]    % Assiging a row
matrix(:)       % Put all the elements into a single column vector

mat_concat = [matrix mat]   % Concatenate matrices side by side [matrix, mat]
mat_concat = [matrix; mat]  % Concatenate matrices one above the other

matrix * mat    % Matrix multiplication
matrix .* mat   % This is element-wise multiplication, similarly .+, ./, .^

matrix'         % Matrix transpose
transpose(matrix)

pinv(matrix)    % Pseudo Inverse matrix 

Iterators

v = 1:0.1:2     % Start:step-size:end deafult step-size is 1

Plotting

a = magic(5)
plot(x, y)              % Makes a two dimensional graph
hold on;                % To plot one or more plots at a time
xlabel("label")         % Label on the x-axis
ylabel("label")         % Label on the y-axis

print -dpng '<filename>'    % To save into a file
subplot(1, 2, 1)        % Divide the figure into 1 row 2 columns and access the 1st figure  

imagesc(a), colorbar, colormap gray;    % Plots using colors

hist(randn(1, 100))     % Plots a histogram hist(<vector>, [bins])

Control Statements

If else

v = zeros(10, 1);

i = 0;
while true,
    v(i) = i*i;
    if i == 6,
        break;
    else
        disp("Value is not 6")
    end;
end;

For

v = zeros(10, 1);

for i=1:10,
    v(i) = i*i;
end;

While

v = zeros(10, 1);

i = 0;
while i < 5,
    v(i) = 10*i;
    i = i + 1;
end;

Functions

function y = squareNumber(x),
    y = x ^ 2;
end;