>>%% dimensions
>> sz=size(A) % 1x2 matrix: [(number of rows) (number of columns)]
sz =
3 2
>> size(A,1) % number of rows
ans = 3
>> size(A,2) % number of cols
ans = 2
>> length(v) % size of longest dimension
ans = 6
>> pwd % show current directory (current path)
ans = /home/arming/coursera/machinelearning/octave
>>%% loading data
>> load q1x.dat % alternatively, load('q1y.dat')
>> load q1y.dat
>> who % list variables in workspace
Variables in the current scope:
A C I a ans b c q1x q1y sz v w
>> whos % list variables in workspace (detailed view)
Variables in the current scope:
Attr Name Size Bytes Class
==== ==== ==== ===== =====
A 3x2 48 double
C 2x3 48 double
I 4x4 32 double
a 1x1 8 double
ans 1x44 44 char
b 1x2 2 char
c 1x1 1 logical
q1x 10x2 160 double
q1y 9x3 216 double
sz 1x2 16 double
v 1x6 24 double
w 1x10000 80000 double
Total is 10131 elements using 80599 bytes
>> clear q1y % clear w/ no argt clears all
>> whos
Variables in the current scope:
Attr Name Size Bytes Class
==== ==== ==== ===== =====
A 3x2 48 double
C 2x3 48 double
I 4x4 32 double
a 1x1 8 double
ans 1x44 44 char
b 1x2 2 char
c 1x1 1 logical
q1x 10x2 160 double
sz 1x2 16 double
v 1x6 24 double
w 1x10000 80000 double
Total is 10104 elements using 80383 bytes
>> v = q1x(1:5) % first 5 elements of q1x (counts down the columns)
v =
1 2 3 4 5
>> save hello v; % save variable v into file hello.mat
>> ls % list files in current directory
hello q1x.dat q1y.dat
>> save hello.txt v -ascii; % save as ascii
>>% fopen, fread, fprintf, fscanf also work [[not needed in class]]
>>%% indexing
>> A(3,2) % indexing is (row,col)
ans = 6
>> A
A =
1 2
3 4
5 6
>> A(2,:) % get the 2nd row.
% ":" means every element along that dimension
ans =
3 4
>> A(:,2) % get the 2nd col
ans =
2
4
6
>> A([1 3],:) % print all the elements of rows 1 and 3
ans =
1 2
5 6
>>A(;,2) = [10; 11; 12] % change second column
A =
1 10
3 11
5 12
>> A = [A, [100; 101; 102]] % append column vec
A =
1 2 100
3 4 101
5 6 102
>> A
A =
1 2 100
3 4 101
5 6 102
>> A(:) % Select all elements as a column vector.
ans =
1
3
5
2
4
6
100
101
102
>>% Putting data together
>> 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]
c =
1 2 11 12
3 4 13 14
5 6 15 16
>> C = [A; B]
C =
1 2
3 4
5 6
11 12
13 14
15 16
>> C = [B A]
C =
11 12 1 2
13 14 3 4
15 16 5 6
>> C = [B; A]
C =
11 12
13 14
15 16
1 2
3 4
5 6
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