Octave is an easy programming language used for solving machine learning problems.
I am transcripting here the lesson I am following on Standford from Andrew Ng. I think that this script is a perfect crash course:
GNU Octave, version 3.2.4
Copyright (C) 2009 John W. Eaton and others.
This is free software; see the source code for copying conditions.
There is ABSOLUTELY NO WARRANTY; not even for MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. For details, type `warranty'.
Octave was configured for "i686-pc-mingw32".
Additional information about Octave is available at http://www.octave.org.
Please contribute if you find this software useful.
For more information, visit http://www.octave.org/help-wanted.html
Report bugs to <bug@octave.org> (but first, please read
http://www.octave.org/bugs.html to learn how to write a helpful report).
For information about changes from previous versions, type `news'.
octave-3.2.4.exe:1> % here I put comment;
octave-3.2.4.exe:1> %first remove the line starter...
octave-3.2.4.exe:1> PS1('>> ');
>> PS1(' -- ');
-- % I will go back to the >> line starter
-- PS1('>> ');
>>
>>
>> % basic operators
>> 10+3
ans = 13
>> 4-2
ans = 2
>> 5*10
ans = 50
>> 50/5
ans = 10
>> 2^3
ans = 8
>>
>>
>> % logic operators
>> 1==2
ans = 0
>> % 0 is false, 1 is true
>> 1==1
ans = 1
>> 1!=2
ans = 1
>> 1~=2
ans = 1
>> 1~=1
ans = 0
>> 1 && 1
ans = 1
>> 1 && 1 % and operator
ans = 1
>> 1 || 1 % or operator
ans = 1
>> 0 || 0
ans = 0
>> 1 || 2
ans = 1
>> 1 && 2
ans = 1
>> % better than to say:
>> % 0 is false; != 0 is true
>> 1 && -1
ans = 1
>> % 0 is false; != 0 is true, by default is represented by 1
>>
>>
> % variable assignment
>> a=3
a = 3
>> % suppress the output return line
>> a=3;
>>
>>
>> % display...
>> a = pi;
>> a
a = 3.1416
>> format long
>> a
a = 3.14159265358979
>> format short
>> a
a = 3.1416
>> disp(a);
3.1416
>> format long
>> disp(a);
3.14159265358979
>> disp(sprintf('only 2 decimals: %0.2f', a))
only 2 decimals: 3.14
>> disp(sprintf('only 5 decimals: %0.5f', a))
only 5 decimals: 3.14159
>> disp(sprintf('only 10 decimals: %0.10f', a))
only 10 decimals: 3.1415926536
>>
>>
>>
>>
>> % matrix
>>
>> A= [1 2; 3 4; 5 6]
A =
1 2
3 4
5 6
>> v = [1 2 3 ]
v =
1 2 3
>> % v is an array
>> % v has dimension 1 x 3
>> % let
>> % let's see now a vector, so a v having dimensions 3 x 1
>> v = [1;2;3]
v =
1
2
3
>> % now interval range arrays
>> v = 1:0.1:2
v =
Columns 1 through 3:
1.00000000000000 1.10000000000000 1.20000000000000
Columns 4 through 6:
1.30000000000000 1.40000000000000 1.50000000000000
Columns 7 through 9:
1.60000000000000 1.70000000000000 1.80000000000000
Columns 10 and 11:
1.90000000000000 2.00000000000000
>> %meta syntax is:
>> % vector = STARTING_AT:DELTA:ENDING_AT
>> v = 1:6
v =
1 2 3 4 5 6
>> % by default the delta is 1
>> %known matrixes
>>
>> w = ones(1,3)
w =
1 1 1
>> w = zeros(1,3)
w =
0 0 0
>> %random
>> r = rand(3,3)
r =
0.567402857515203 0.301184329285262 0.830303110034579
0.703828527889656 0.800885232762887 0.876086413236985
0.340103401896943 0.675342891105335 0.242842578966916
>> r = rand(3,3)
r =
0.4699204825787972 0.4124515864382686 0.9827575401589607
0.0118059148057477 0.4695877000100873 0.6805667208195990
0.9936553157929338 0.9727665315772230 0.1624513014665614
>> r = rand(3,3)
r =
0.17186568773859429 0.22565708518331024 0.28727929514480505
0.91982345102655927 0.77380397661275846 0.00322060012954977
0.42991791381680561 0.25561768241919586 0.62438590998652621
>> % some more complex stuff
>>
>>
>>
>>
>> g = -6 + sqrt(10)
g = -2.83772233983162
>> rand(1,1000)
>> g = -6 + sqrt(10)*randn(1,10000)
>> hist(g)
>> % here comes out a histogram window...
>> hist(g,50)
>> % here it comes out a histogram window with 50 columns
>>
>>
>>
>> % generate the identity matrix
>> I = eye(3);
>> I
I =
Diagonal Matrix
1 0 0
0 1 0
0 0 1
>>
>>
>> % helper
>> help eye
>> % here it comes out a helper description of the function...
>>
>>
>> A = [1,2;3,4;5,6]
A =
1 2
3 4
5 6
>> sz = size(A) %get the dimensions of the matrix
sz =
3 2
>> size(sz)
ans =
1 2
>> size(A,1) %get the nr of rows of the matrix
ans = 3
>> size(A,2) %get the nr of cols of the matrix
ans = 2
>> v = [1,2,3,4]
v =
1 2 3 4
>> length(v) %get the max dimension
ans = 4
>> length(A)
ans = 3
>> who %results below come from a different session.... values probably wrong... it just gives an idea
Variables in the current scope:
A ans sz v
>> whos %results below come from a different session.... values probably wrong... it just gives an idea
Variables in the current scope:
Attr Name Size
==== ==== ====
A 3x2
ans 9x1
sz 1x2
v 1x4
Total is 41 elements using 328 bytes
>>
>> A(3,2) % gives you the element in position: row 3, col 2
ans = 6
>> A(3,:) % gives you the elements in position: row 3, complete row
ans =
5 6
>> A(:,2) % gives you the elements in position: col 2, complete column
ans =
2
4
6
>> A([1 3], :) % gives you the elements in position: row 1 and 3, complete row
ans =
1 2
5 6
>> A(:, 2) = [10;11;12] % assign complete column
A =
1 10
3 11
5 12
>> A = [A, [100; 101; 102]] % extend the matrix, adding a new column
A =
1 10 100
3 11 101
5 12 102
>> size(A)
ans =
3 3
>> A(:) % transform a matrix into a vector
ans =
1
3
5
10
11
12
100
101
102
>>
>>
>> A = [1,2;3,4;5,6]
A =
1 2
3 4
5 6
>> B= [11 12; 13 14; 15 16]
B =
11 12
13 14
15 16
>> C = [A B] % put two matrix one beside the other
C =
1 2 11 12
3 4 13 14
5 6 15 16
>> C = [A; B] % put two matrix one on top of the other
C =
1 2
3 4
5 6
11 12
13 14
15 16
>>
