octave tutorial
Tags: octave
Octave - Basic Operations
- 基本
# 普通運算 5 + 6 3 - 2 5 * 8 1 / 2 2 ^ 8 # 判斷 1 == 2 (等於) ---> 0 [false] 1 ~= 2 (不等於) ---> 1 [true] # 邏輯 1 && 0 (AND) 1 || 0 (OR) xor(1,0) - 變數
a = 3 >> a = 3 % semicolon supressing output a = 3; - print 出來
a = 3; a >> a = 3 b = pi; disp(b) >> 3.1416 % 印string disp(sprintf('2 decimals: %0.2f', b)) >> 2 decimals: 3.14 % formt format long b >> b = 3.141592653589793 format short b >> b = 3.1416 - vectors and matrix
% Matrix: A = [1 2; 3 4; 5 6] A = 1 2 3 4 5 6 % (1,3) matrix v = [1 2 3] v = 1 2 3 % column vector % (3,1) vector: v = [1; 2; 3] v = 1 2 3 % v = (start):(increment step):(end) v = 1:0.1:2 v = 1.0000 1.1000 1.2000 1.3000 1.4000 1.5000 1.6000 1.7000 1.8000 1.9000 2.0000 % (1,11) matrix % ones matrix ones(2,3) ans = 1 1 1 1 1 1 c = 2 * ones(2,3) c = 2 2 2 2 2 2 % zeros matrix w = zeros(1, 3) z = 0 0 0 % random matrix rand(3, 3) ans = 0.423904 0.116361 0.585396 0.372444 0.481492 0.365303 0.079343 0.557110 0.843614 % random normal distribution randn(1, 3) ans = -0.051417 1.221825 -0.964078 % identity matrix eye(4) ans = Diagonal Matrix 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 - 出圖
w = -6 + sqrt(10)*(randn(1, 10000)); hist(w) % eye() -
help
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.
Moving Data Around
- size & length
A = [1 2; 3 4; 5 6] A = 1 2 3 4 5 6 size(A) ans = 3 2 size(A, 1) >> ans = 3 size(A, 2) >> ans = 2 % length --> return the longest value (row or column) v = [1, 3, 4, 5, 9] length(v) >> ans = 5 length(A) >> ans = 3 length([10;22;33;44;55;100]) >> ans = 6 - load data
% pwd (show current directory) Ex: pwd >> ans = E:\Coursera\Machine_Learning\octave-5.1.0-w64 % cd 你知我知 % ls 我知你知 % load load xxx.files load('xxx.files') % who - showing what variables in octave EX: who >> Variables in the current scope: A a ans b c v w z % whos - give you detail EX: whos >> Variables in the current scope: Attr Name Size Bytes Class ==== ==== ==== ===== ===== A 3x2 48 double a 1x1 8 double ans 1x45 45 char b 1x1 8 double c 2x3 48 double v 1x4 32 double w 1x10000 80000 double z 1x3 24 double Total is 10066 elements using 80213 bytes % clear - clear variable EX: clear A whos >> Variables in the current scope: Attr Name Size Bytes Class ==== ==== ==== ===== ===== a 1x1 8 double ans 1x45 45 char b 1x1 8 double c 2x3 48 double v 1x4 32 double w 1x10000 80000 double z 1x3 24 double Total is 10066 elements using 80213 bytes % save - save file EX: save xxx.txt a %save variable a to xxx.txt in current pwd - manipulate variable
A = [1 2; 3 4; 5 6] A = 1 2 3 4 5 6 A(3,2) ans = 6 % ":" means every element along that row/column A(2, :) ans = 3 4 A(:, 2) ans = 2 4 6 A(:, 2) = [10; 11; 12] A = 1 10 3 11 5 12 % append another column vector to right A = [A, [100; 101; 102]] A = 1 10 100 3 11 101 5 12 102 % put all elements of A into a single vector A(:) ans = 1 3 5 10 11 12 100 101 102 % concat matrix A = [ 1 2; 3 4; 5 6] 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