Here is a simple Octave Primer. Octave is a powerful language for implementing Machine Learning algorithms. As I have mentioned its strength is its simplicity. I am including some basic commands with which you can get by implementing fairly complex code

%%Matrix

A matrix can be created as `a = [1 2 3; 4 7 8; 12 35 14]; `

% This is 3 x 3 matrix

Matrix multiplication can be done between m x n * n x k matrix as follows

`a = [4 56 3; 2 3 4]; b = [23 1; 3 12; 34 12]; % a = 3 x 2 matrix b = 2 x 3 matrix`

c = a*b; %% c = 3 x 2 * 2 * 3 = 3 x 3 matrix

`c =`

362 712

191 86

%%Inverse of a matrix can be obtained by

`d = pinv(c);`

octave-3.2.4.exe:37> d = pinv(c)

d =

-8.2014e-004 6.7900e-003

1.8215e-003 -3.4522e-003

%%Transpose of a matrix

`e = c'; % e is the transpose of done`

`octave-3.2.4.exe:38> e = c'`

e =

362 191

712 86

The following operations are done on all elements of a matrix or a vector

`k = 5;`

a = [1 2; 3 4; 5 6]; k = 5.23;

c = k * a;

d = a - 2

e = a / 5

f = a .* a % Dot product

g = a .^2; % Square each elements

%% Select slice of matrix

`b = a(:,2); % Select column 2 of matrix a (all rows)`

c = a(2,:) % Select row of matrix 'a' (all columns)

`d = [7 8; 8 9; 10 11; 12 13]; % 4 rows 2 columns`

d(2:3,:); %Select from rows 2 to 3 (all columns)

`octave-3.2.4.exe:41> d`

d =

7 8

8 9

10 11

12 13

octave-3.2.4.exe:43> d(2:3,:)

ans =

8 9

10 11

%% Appending rows to matrix

`a = [ 4 5; 5 6; 5 7; 9 8]; % 4 x 2`

b = [ 1 3; 2 4]; % 2 x 2

c = [ a; b] % stack a over b

d = [b ; a] % stack b over a*b

`octave-3.2.4.exe:44> a = [ 4 5; 5 6; 5 7; 9 8] % 4 x 2`

a =

4 5

5 6

5 7

9 8

octave-3.2.4.exe:45>` b = [ 1 3; 2 4] % 2 x 2`

b =

1 3

2 4

octave-3.2.4.exe:46> `c = [ a; b] % stack a over b`

c =

4 5

5 6

5 7

9 8

1 3

2 4

octave-3.2.4.exe:47> `d = [b ; a] % stack b over a*b`

d =

1 3

2 4

4 5

5 6

5 7

9 8

%% Appending columns

`a = [ 1 2 3; 3 4 5]; b = [ 1 2; 3 4];`

c = [a b];

d = [b a];

`octave-3.2.4.exe:48> a = [ 1 2 3; 3 4 5]`

a =

1 2 3

3 4 5

octave-3.2.4.exe:49>` b = [ 1 2; 3 4]`

b =

1 2

3 4

octave-3.2.4.exe:50> `c = [a b]`

c =

1 2 3 1 2

3 4 5 3 4

octave-3.2.4.exe:51>` d = [b a]`

d =

1 2 1 2 3

3 4 3 4 5

%%Size of a matrix

[c d ] = size(a);

Creating a matrix of all zeros or ones

`d = ones(3,2);`

e = zeros(4,3);

%Appending an intercept term to a matrix

`a = [1 2 3; 4 5 6]; %2 x 3`

b = ones(2,1);

a = [b a];

%% Plotting

Creating 2 vectors

`x = [1 3 4 5 6];`

y = [5 6 7 8 9];

plot(x,y);

%%Create labels

`xlabel("X values); ylabel("Y values);`

axis([1 10 4 10]); % Set the range of x and y

title("Test plot);

%%Creating a 3D scatter plot

If we have 3 column csv file then we can load the data as follows

`data = load('values.csv');`

X = data(:, 1:2);

y = data(:, 3);

scatter3(X(:,1),X(:,2),y,[],[240 15 15],'x'); % X(:,1) - x axis X(:,2) - yaxis y[] - z axis

%% Drawing a 3D mesh

`x = linspace(0,xrange + 20,10);`

y = linspace(1,yrange+ 20,10);

[XX, YY ] = meshgrid(x,y);

[a b] = size(XX)

Draw the mesh

`for i=1:a,`

for j= 1:b,

ZZ(i,j) = [1 (XX(i,j)-mu(1))/sigma(1) (YY(i,j) - mu(2))/sigma(2) ] * theta;

end;

end;

mesh(XX,YY,ZZ);

For more details please see post Informed choices using Machine Learning 2- Pitting Kumble, Kapil and B S Chandra

%% Creating different polynomial equations

Let X be a feature vector

then

X = [X X.^2 X^3] %X X^2 X^3

This can be created using a for loop as follows

`for i= 1:n`

xtemp = xinput .^i;

x = [x xtemp];

end;

Finally while doing multivariate regression if we wanted to create polynomial terms of higher we could do as follows. Let us say we have a feature vector X made of 3 features x1, x2,

Let us say we wanted to create a polynomial of the form x1^2 x1.x2 x2^2 then we could create X as

`X = [X(:,1) .^2 X(:,1) . X(:,2) X(:,2) .^2]`

As you can see Octave is really powerful language for Machine Learning and has just a few handful of constructs with which one can implement powerful Machine Learning algorithms

Good primer

Can become better with a little proof reading

—

c = a*b; %% c = 3 x 2 * 2 * 3 = 3 x 3 matrix

d = [b ; a] % stack b over a*b

and few more

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Thanks Rohit. Corrected.

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