%: stand for comment
~=: stand for unequal
Semicolon will suppress output
disp:
octave:6> a = pi;
octave:7> disp(sprintf('2 decimal: %0.2f', a))
2 decimal: 3.14
- format long && format short
octave:8> format long
octave:9> a
a = 3.141592653589793
octave:10> format short
octave:11> a
a = 3.1416
octave:12>
- Generate a matrix or a vector
octave:12> matrix_a = [1 2; 3 4; 5 6];
octave:13> matrix_a
matrix_a =
1 2
3 4
5 6
octave:14> vector_a = [1 2 3]
vector_a =
1 2 3
octave:15> vector_b = 1:0.1:2
vector_b =
Columns 1 through 8:
1.0000 1.1000 1.2000 1.3000 1.4000 1.5000 1.6000 1.7000
Columns 9 through 11:
1.8000 1.9000 2.0000
octave:14> vector_a = [1 2 3]
vector_a =
1 2 3
octave:15> vector_b = 1:0.1:2
vector_b =
Columns 1 through 8:
1.0000 1.1000 1.2000 1.3000 1.4000 1.5000 1.6000 1.7000
Columns 9 through 11:
1.8000 1.9000 2.0000
octave:16> vector_c = 1:6
vector_c =
1 2 3 4 5 6
- Get a part of matrix:
octave:21> matrix_a(3, 2)
ans = 6
octave:22> matrix_a(3, :)
ans =
5 6
octave:23> matrix_a(:, 2)
ans =
2
4
6
octave:24> matrix_a([1, 3], :)
ans =
1 2
5 6
- Reassign the value in matrix
octave:25> matrix_a(:, 2) = [10, 11, 12]
matrix_a =
1 10
3 11
5 12
- Append a vector in matrix:
octave:27> [matrix_a, [20; 21; 22]]
ans =
1 10 20
3 11 21
5 12 22
- Put all element together in a column vector
octave:28> matrix_a(:)
ans =
1
3
5
10
11
12
- Concatenate matrix
octave:29> matrix_a = [1 2; 3 4; 5 6]
matrix_a =
1 2
3 4
5 6
octave:30> matrix_b = [11 12; 13 14; 15 16]
matrix_b =
11 12
13 14
15 16
octave:31> matrix_c = [matrix_a matrix_b]
matrix_c =
1 2 11 12
3 4 13 14
5 6 15 16
octave:32> matrix_d = [matrix_a; matrix_b]
matrix_d =
1 2
3 4
5 6
11 12
13 14
15 16
- Print a histogram
octave:1> w = -6 + sqrt(10)*(randn(1, 10000));
octave:2> hist(w)
octave:3>
Screen Shot 2019-03-23 at 23.27.18.png
- Generate an identity matrix
octave:1> eye(5)
ans =
Diagonal Matrix
1 0 0 0 0
0 1 0 0 0
0 0 1 0 0
0 0 0 1 0
0 0 0 0 1
- size
octave:4> size(matrix_a)
ans =
3 2
octave:5> size(matrix_a, 1)
ans = 3
octave:6> size(matrix_a, 2)
ans = 2
- length: return the longest dimension of matrix
octave:7> length(matrix_a)
ans = 3
- who && whos: List all variables in current scope
octave:9> who
Variables in the current scope:
ans matrix_a
octave:10> a = 1
a = 1
octave:11> who
Variables in the current scope:
a ans matrix_a
octave:12> whos
Variables in the current scope:
Attr Name Size Bytes Class
==== ==== ==== ===== =====
a 1x1 8 double
ans 1x15 15 char
matrix_a 3x2 48 double
- pwd: show the current location
octave:8> pwd
ans = /Users/xxx
- load: to import data files
octave:25> load('ex1data1.txt')
octave:26> whos
Variables in the current scope:
Attr Name Size Bytes Class
==== ==== ==== ===== =====
ans 1x25 25 char
ex1data1 97x2 1552 double
h0 1x101 808 double
y 1x101 808 double
y2 1x101 808 double
- clear : to delete a variable
octave:15> clear a
octave:16> whos
Variables in the current scope:
Attr Name Size Bytes Class
==== ==== ==== ===== =====
ans 1x25 25 char
matrix_a 3x2 48 double
Total is 31 elements using 73 bytes
- help
see document
octave:2> help eye
'eye' is a built-in function from the file libinterp/corefcn/data.cc
-- eye (N)
-- eye (M, N)
-- eye ([M N])
-- eye (..., CLASS)
Return an identity matrix.
If invoked with a single scalar argument N, return a square NxN
identity matrix.
If supplied two scalar arguments (M, N), 'eye' takes them to be the
number of rows and columns. If given a vector with two elements,
'eye' uses the values of the elements as the number of rows and
columns, respectively. For example:
eye (3)
=> 1 0 0
0 1 0
0 0 1
The following expressions all produce the same result:
eye (2)
==
eye (2, 2)
==
eye (size ([1, 2; 3, 4]))
The optional argument CLASS, allows 'eye' to return an array of the
specified type, like
val = zeros (n,m, "uint8")
Calling 'eye' with no arguments is equivalent to calling it with an
argument of 1. Any negative dimensions are treated as zero. These
odd definitions are for compatibility with MATLAB.
See also: speye, ones, zeros.
Additional help for built-in functions and operators is
available in the online version of the manual. Use the command
'doc <topic>' to search the manual index.
Help and information about Octave is also available on the WWW
at https://www.octave.org and via the help@octave.org
mailing list.
