Octave学习记录
1.Basic operations
%generate a matrix
a = [1,2,3;4,5,6]
a =
1 2 3
4 5 6
a = [1,2,3;4,5,6]; % The end ';' will inhibit the output of assignment operation
%generate a vaector
a = [1 2 3];
a = [1:3];
%specific matrix or vectors
ones(3,1)
zeros(0,1)
a = ones(3,1);
a(1) = 0;
a
%change or add one row or one column of a matrix
octave:33> a = [1 2 3];
octave:34> a = [a;a]
a =
1 2 3
1 2 3
octave:35> a = [a a]
a =
1 2 3 1 2 3
1 2 3 1 2 3
octave:36> a = [a a ones(2,1)]
a =
1 2 3 1 2 3 1 2 3 1 2 3 1
1 2 3 1 2 3 1 2 3 1 2 3 1
octave:37> a = [a ; ones(1,size(a,2))]
a =
1 2 3 1 2 3 1 2 3 1 2 3 1
1 2 3 1 2 3 1 2 3 1 2 3 1
1 1 1 1 1 1 1 1 1 1 1 1 1
octave:38> a[1,]
parse error:
syntax error
>>> a[1,]
^
octave:38> a[1,:] = zeros(1,size(a,2))
parse error:
syntax error
>>> a[1,:] = zeros(1,size(a,2))
^
octave:38> a(1,:) = zeros(1,size(a,2))
a =
0 0 0 0 0 0 0 0 0 0 0 0 0
1 2 3 1 2 3 1 2 3 1 2 3 1
1 1 1 1 1 1 1 1 1 1 1 1 1
octave:39> a(:,1) = ones(size(a,1),1)
a =
1 0 0 0 0 0 0 0 0 0 0 0 0
1 2 3 1 2 3 1 2 3 1 2 3 1
1 1 1 1 1 1 1 1 1 1 1 1 1
2.Get the maximum value from a matrix
octave:12> a = [1,2,3;4,5,6;7,8,9] a = 1 2 3 4 5 6 7 8 9 octave:13> max(a) #default by columns ans = 7 8 9 octave:14> [value, index] = max(a) #return the largest value of each column and their rows value = 7 8 9 index = 3 3 3
3.Get unique values of a vector
octave:23> a = [1 2 3 4 5 1 2 3 4 5 1 2 3 4 5] a = 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 octave:24> unique(a) ans = 1 2 3 4 5
4.Get the number of rows and columns of a mtrix
octave:27> a = [1 2 3 4 5; 1 2 3 4 5 ;1 2 3 4 5]
a =
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
octave:28> size(a)
ans =
3 5
octave:29> size(a,1) % number of rows
ans = 3
octave:30> size(a,2) % number of columns
ans = 5
octave:31> a = [1 2 3 4 5 1 2 3 4 5 1 2 3 4 5]
a =
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
octave:32> size(a)
ans =
1 15
5.Get the position of one special value or change one special value to 0
octave:48> a = [ones(5,1);zeros(5,1)];
octave:49> pos_a = find(a==1)
pos_a =
1
2
3
4
5
octave:50> a(pos_a,:)
ans =
1
1
1
1
1
octave:51> zero_a = find(a==0)
zero_a =
6
7
8
9
10
octave:52> a(zero_a,:)
ans =
0
0
0
0
0
%------------------------------------------
octave:53> a = [1,2,3,4,5,1,2,3,4,5]
a =
1 2 3 4 5 1 2 3 4 5
octave:54> a == 1
ans =
1 0 0 0 0 1 0 0 0 0
octave:55> a == 5
ans =
0 0 0 0 1 0 0 0 0 1
6.repmat — repeat a given matrix by given number of times in row and column
octave:24> a = ones(3,4) a = 1 1 1 1 1 1 1 1 1 1 1 1 octave:25> repmat(a,1,2) ans = 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 octave:26> repmat(a,2,2) ans = 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
7.
- 9.
