GNU Octave is a really neat prototyping language for machine learning tasks. It is dynamically typed.
Installation
Octave is in the package repositories, so it can be installed by
$ sudo apt-get install octave gnuplot-x11 octave-epstk
and started with
$ octave
Configuration
Create a file ~/.octaverc in your home folder. Write
PS1('>>');
setenv("GNUTERM","x11");
in it to get a nicer prompt and make sure that plots will work.
The Language
Vectors and Matrices
Octave has a lot of neat matrix manipulation features. You can create a matrix
\(A =
>> A = [1 2; 3 4];
When you want to transpose a vector / a matrix, you simply add an apostrophe:
>> A = [1 2; 3 4];
>> A'
ans =
1 3
2 4
You can multiply two matrices with A*B or use the dot product with A .* B.
The identity matrix \(I \in \mathbb{R}^{n \times n}\) can be created with
>> I = eye(n);
You can get a part of the matrix by slicing:
>> I = eye(n);
>> I(:, 1:2);
But be careful: Vectors and matrices are 1-indexed, not 0-indexed as you might expect!
You can get the size of a matrix with the function size which returns a matrix:
>> a = [1 2 3; 4 5 6];
>> size(a)
ans =
2 3
If you simple want the "length" you can directly access the first element:
>> size(a)(1)
ans = 2
Sequences
The sequence 0 1 2 3 4 5 can be created with [0:5].
The sequence 0.2 0.3 0.4 0.5 can be created with [0.2:0.1:0.5].
In general: [<start>:<step>:<end>] where <start> and <end> are included.
You can also very simple apply functions to each element:
>> t = [0.2:0.1:0.5];
>> sin(t)
ans =
0.19867 0.29552 0.38942 0.47943
The output can be suppressed with ;.
Plotting
I have never seen a language where plotting is so easy:
>> x = [0:0.01:pi];
>> y = sin(x);
>> plot(x, y);
You can add labels and a legend to it, too:
>> xlabel = "x";
>> ylabel = "value";
>> legend('sin', 'cos')
>> title("sin and cos")
And finally, you can store the image:
print -dpng 'my_plot.png'
Control statements
for
for i=1:10;
printf("%i: %i\n", i, i^2)
end
while
i=1;
while i <= 10,
printf("%i: %i\n", i, i^2)
end;
if
if 2 == 1+1,
printf("True\n");
elseif 3 == 2+1,
printf("Else true");
else
printf("else");
end;
Functions
Functions have to be saved in a file called [filename].m. One other special
thing about functions is that you define the variable with the output at the
beginning:
function y = fibonacci(n)
if n < 2,
y = 1;
else
y = fibonacci(n-1) + fibonacci(n-2);
end;
You can also group values you want to give back like this:
function [succ, pred] = succ_and_pred(n)
succ = n+1;
pred = n-1;