Installation on Archlinux：sudo pacman -S octave,enter the shell：octave,shows the following:
GNU Octave, version 5.1.0 Copyright (C) 2019 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 "x86_64-pc-linux-gnu".
Additional information about Octave is available at https://www.octave.org.
Please contribute if you find this software useful. For more information, visit https://www.octave.org/get-involved.html
Read https://www.octave.org/bugs.html to learn how to submit bug reports. For information about changes from previous versions, type 'news'.
octave:1>
Basic opeation
common variables
octave:5> 1+1 ans = 2 octave:6> 3-6 ans = -3 octave:7> 5*3 ans = 15 octave:8> 4/5 ans = 0.80000 octave:9> 1==2 %false ans = 0 octave:10> 1==1 %true ans = 1 octave:11> 1 && 0 % AND ans = 0 octave:12> 1 || 0 % OR ans = 1
use PS1() to change the default prompt:
octave:14> PS1('( つ•̀ω•́)つ ') ( つ•̀ω•́)つ A = [1,2,3;4,5,6;7,8,9] A =
1 2 3 4 5 6 7 8 9 ( つ•̀ω•́)つ PS1('>>') >>
semicolon supress output
>> a = 3 a = 3 >> a = 3; >> a a = 3 >> a;
disp() is used to display,sprintf() is used to format string output:
>>pi = 3.1415926; >>disp(pi) 3.1416 >>disp(sprintf('pi is: %0.2f',pi)) pi is: 3.14
format [long|short] is used to change the precision.
matrix and vector
A is a 3x2 matrix,x is a 3x1 vector,y is a 1x3 vector. ones() returns a matrix with all elements 1. zeros() returns a matrix with all elements 0. rand() returns a matrix with all elements random number. eye() returns a identity matrix. size() returns the size of the matrix. length() returns the larger dimension of the matrix,for vector it returns the length of it. A(x,y) returns the A[x][y] element.
>>A = [1,2,3;4,5,6] A =
1 2 3 4 5 6
>>A(1,3) ans = 3
>>A(2,:) % means every element along that column/row ans =
4 5 6
>>A(:,[1,2]) ans =
1 2 4 5
>>size(A) ans =
2 3
>>x = [3;4;5] x =
3 4 5
>>y = [1,2,3] y =
1 2 3
>>v = 1:6 v =
1 2 3 4 5 6
>>v = [1 2 3 4] v =
1 2 3 4
>>length(A) ans = 3 >>length(v) ans = 4
>>ones(2,3) ans =
1 1 1 1 1 1
>>eye(3) ans =
Diagonal Matrix
1 0 0 0 1 0 0 0 1
>>A = [A,[7;8]] % append a column to matrix A =
1 2 3 7 4 5 6 8
>>A(:) % put all elements of A into a single vector ans =
1 4 2 5 3 6 7 8
>>A = [A;[9,10,11,12]] % append a row to the matrix A =
1 2 3 7 4 5 6 8 1 2 3 4 9 10 11 12
use hist() to plot a histogram
>>w = randn(1,10000) >>hist(w)
Data Persist
use help <cmd> to refer to the manual of cmd
>>help eye >>help rand
use pwd to get present working directory,use cd to change directory,ls to list the files:
>>pwd ans = /home/xuranus >>cd ~/Desktop/ >>pwd ans = /home/xuranus/Desktop
use who to list all the variable in current working space while whos list the detail. save(filename) can save all the data to the disk,when the second variable is speified like save('xxx',v),only the specified variable v will be persisted .clear can clear all the data,and then we use whoagain to check if there exists any variable(of course there doesn’t).By using load(filename) we can restore the variable we cleared from file.
>>who Variables in the current scope: A a ans p pi v w x y >>save('test1.dat') >>ls test.dat >>clear >>who >>load('test1.dat') >>whos Variables in the current scope:
Attr Name Size Bytes Class ==== ==== ==== ===== ===== A 2x3 48 double a 1x1 8 double ans 1x21 21 char p 3x1 24 double pi 1x1 8 double v 1x4 32 double w 1x10000 80000 double x 3x1 24 double y 1x3 24 double
Total is 10042 elements using 80189 bytes
Computing On Data
. denotes element wise operation,which is different from common matrix arthmetic operation. pinv() returns the reverse of A. A' means transpose of matrix A.
>>> A = [1 2; 3 4; 5 6] A =
1 2 3 4 5 6
>>> B = [4 5 6;7 8 9] B =
4 5 6 7 8 9
>>> A' ans =
1 3 5 2 4 6
>>> A*B ans =
18 21 24 40 47 54 62 73 84
>>> A.*B error: product: nonconformant arguments (op1 is 3x2, op2 is 2x3) >>> C = [6 7 8;9 10 11] C =
6 7 8 9 10 11
>>> B.*C ans =
24 35 48 63 80 99
>>> B./C ans =
0.66667 0.71429 0.75000 0.77778 0.80000 0.81818
>>> B.+C ans =
10 12 14 16 18 20
>>> A.^2 % element-wise square ans =
1 4 9 16 25 36
when a single parameter function applied to vector or matrix, it performs an element-wise operation.
>>> v = 1:6 v =
1 2 3 4 5 6
>>> log(v) ans =
0.00000 0.69315 1.09861 1.38629 1.60944 1.79176
the use of max(vector):
>> A A =
1 2 3 4 5 6
>> v = 1:6 v =
1 2 3 4 5 6
>> max(v) % return the maximum number ans = 6 >> [num,index] = max(v) % return the maximum number and corresponding index num = 6 index = 6 >> max(A) ans =
5 6
>> v>3 % return each element is larger than 3 or not ans =
0 0 0 1 1 1
octave:10> find(v>3) % filter the element larger than 3 ans =
4 5 6
magic() returns a nxn matrix whose row, column, diagnoal add up to the same thing.
>> magic(3) ans =
8 1 6 3 5 7 4 9 2
prod() returns the product of vector. sum() return the sum of the vector. ceil() means get rounded up while floor() means get rounded down.
>>> v = [1 6 4 3.5] v =
1.0000 6.0000 4.0000 3.5000
>>> prod(v) ans = 84 >>> sum(v) ans = 14.500 >>> floor(v) ans =
1 6 4 3
>>> ceil(v) ans =
1 6 4 4
max(A1,A2) returns a new matrix ,every element of which is the larger one. max(A,[],1) compares the first dimension(the column) and returns a vector ,the ith element is the maximum in the ith column. if you need to find the maximum number in A,you can type max(max(A)) or max(A(:))
>>> A = magic(3) A =
8 1 6 3 5 7 4 9 2
>>> B = A' B =
8 3 4 1 5 9 6 7 2
>>> max(A,B) ans =
8 3 6 3 5 9 6 9 2
>>> max(A,[],1) ans =
8 9 7
>>> max(A,[],2) ans =
8 7 9
sum(A) and sum(A,1) returns the sum of each column in matrix A. sum(A,2) return the sum of each row in matrix. if we need to calculate sum of all elements in A, we can use sum(sum(A)) or sum(A(:))
