机器学习入门第三篇——Octave/Matlab Tutorial（3）

• Moving Data Around
• Compution on Data

Moving Data Around

pwd  %显示路径

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load %加载数据
loa() %加载数据

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who %有哪些变量
whos %显示更多细节

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v=priceY(1:10) %将priceY的前十个元素加载

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save hello.mat 
save hello.txt v-ascii

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A(2,:)  % " : " means every element along that row or column
A(:,2)  % the second column of A
A([1 3],:) % get all the element along that row or column = get first row and thrid row (all columns)
A(:,2)=[10;11;12] %给第二行赋值
A=[A,[10;11;12]] % append another column vector 
A(:) % put all elements of A into a single vector

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A=[1 2; 3 4; 5 6]
B=[11 12; 13 14; 15 16]

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C=[A;B] %将B的元素放在A的元素后行
C=[A B] %将A和B合在一起

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Computing on Data

 A=[1 2; 3 4; 5 6]
 B=[11 12; 13 14; 15 16]
 C=[1 1 ; 2 2]
 A*C
 A.*B % " . " means element-wise operation
 A.^2

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 V=[1 ; 2 ; 3]
 1./V
 log(V) % element-wise 表示对每一个元素取其对数
 exp(V) % element-wise 表示对每一个元素取其自然指数

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abs(A) % 表示对A的每一个元素取绝对值
-V % -1*V 
V+ones(length(V),1) % V的每一个元素加一
 V+1 % V的每一个元素加一 means to add one element-wise each of my elements of V

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ones(3) % 三行三列方阵
ones(3,1) % 三行一列矩阵

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A' % A的转置

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 a=[1 15 2 0.5];
 
 val=max(a) % a的最大值
 [val,ind]=max(a) % ind代表下标
 
 max(A)
 A
 
 a
 a<3  % 比3小的显示true，比3大的显示false
  find(a<3) % 找比3小的下标

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