matlab 机器学习入门
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根据吴恩达机器学习教程总结，在matlab、octave均可使用
Matlab进行标量运算
>> 5 + 5
ans =
10
>> 6 * 2
ans =
12
>> 3^2
ans =
9
>> 3/2
ans =
1.5000
变量赋值
>> a = 3
a =
3
赋值语句后面加; 可以不输出结果
>> q = 3;
>> q
q =
3
字符输入时必须是单引号
>> b =‘hi‘;
>> b
b =
hi
并 或 运算
>> 1 && 0
ans =
0
>> 1||1
ans =
1
比较语句
>> 2 > 3
ans =
0
输出字符串
>> a =pi
a =
3.1416
>> disp(a)
3.1416
>> disp(sprintf(‘2 decimals: %0.2f‘,a))
2 decimals: 3.14
>> sprintf(‘hi‘)
ans =
hi
矩阵表示：
>> A = [1 2;3 4]
A =
1 2
3 4
向量表示
>> V = [1;2;3]
V =
1
2
3
从 1 开始 到2 终止步长为0.1的行向量
>> 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
1X2 全为1 矩阵
>> ones(1,2)
ans =
1 1
2X2全为0矩阵
>> zeros(2,2)
ans =
0 0
0 0
随机1X3 的矩阵
>> rand(1,3)
ans =
0.8147 0.9058 0.1270
对角线为全为1 的单位矩阵
>> eye(4)
ans =
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
help 查看内置函数的用法
>> help eye
eye Identity matrix.
eye(N) is the N-by-N identity matrix.
eye(M,N) or eye([M,N]) is an M-by-N matrix with 1‘s on
the diagonal and zeros elsewhere.
eye(SIZE(A)) is the same size as A.
eye with no arguments is the scalar 1.
eye(..., CLASSNAME) is a matrix with ones of class specified by
CLASSNAME on the diagonal and zeros elsewhere.
eye(..., ‘like‘, Y) is an identity matrix with the same data type, sparsity,
and complexity (real or complex) as the numeric variable Y.
Note: The size inputs M and N should be nonnegative integers.
Negative integers are treated as 0.
Example:
x = eye(2,3,‘int8‘);
See also speye, ones, zeros, rand, randn.
eye 的参考页
名为 eye 的其他函数
判断矩阵的形状
>> size(a)
ans =
1 1
>> size(A,1)
ans =
2
>> v = [1 2 3 4]
v =
1 2 3 4
>> size(v)
ans =
1 4
>> length(v)
ans =
4
显示当前工作目录（与Linux较为相似）
>> pwd
ans =
C:\Program Files\MATLAB\R2016a
进入某一目录
>> cd ‘C:\Users\scz\Desktop‘
>> pwd
ans =
C:\Users\scz\Desktop
显示当前目录下所有文件
>> ls
.
..
1.docx
123
读入文件，并保存到变量中
>> load(‘loldata.csv‘)
>> loldata
loldata =
7.0000 5.0000 2.0000 0.9329 28.7941 5.9861 4.5984
2.0000 1.0000 3.0000 0.4512 2.5701 0.9661 1.2014
7.0000 5.0000 3.0000 0.8364 21.6821 6.0617 3.8332
19.0000 2.0000 1.0000 1.0947 36.3245 12.7096 3.7969
4.0000 2.0000 4.0000 0.8193 19.6814 2.3778 1.3344
2.0000 9.0000 2.0000 0.7157 14.4339 3.3351 6.3405
0 10.0000 6.0000 0.7573 12.3280 2.1769 5.3543
8.0000 5.0000 1.0000 0.9012 20.2787 5.1798 3.9495
3.0000 7.0000 1.0000 0.7876 10.5917 2.2607 6.4620
1.0000 8.0000 4.0000 0.6336 5.9939 1.8080 5.9950
>> size(loldata)
ans =
10 7
显示当前所有变量
>> who
您的变量为:
A V a ans b c loldata q v
所有变量具体信息
>> whos
Name Size Bytes Class Attributes
A 2x2 32 double
V 1x11 88 double
a 1x1 8 double
ans 1x2 16 double
b 1x2 4 char
c 1x1 8 double
loldata 10x7 560 double
q 1x1 8 double
v 1x4 32 double
保存变量到文件中
>> save hello.mat v;
矩阵运算
>> A = [1 2; 3 4 ; 5 6]
A =
1 2
3 4
5 6
>> C = [1 1 ; 2 2]
C =
1 1
2 2
>> A * C
ans =
5 5
11 11
17 17
注意A 后面有空格，.是对矩阵中所有元素进行位运算
>> A .^ 2
ans =
1 4
9 16
25 36
>> A + 1
ans =
2 3
4 5
6 7
>> A
A =
1 2
3 4
5 6
矩阵的转置
>> A‘
ans =
1 3 5
2 4 6
没一列中所有最大元素
>> max(A)
ans =
5 6
>> [VAL,IND] = max(A)
VAL =
5 6
IND =
3 3
矩阵的比较运算
>> A < 3
ans =
1 1
0 0
0 0
所有元素中符合条件位置
>> find(A < 3)
ans =
1
4
>> a = magic(4)
a =
16 2 3 13
5 11 10 8
9 7 6 12
4 14 15 1
>> [r,c] = find(A < 3)
r =
1
1
c =
1
2
>> a = [1 2 3 4]
a =
1 2 3 4
>> sum(a)
ans =
10
>> prod(a)
ans =
24
>> a = [1 2 3 4;1 3 4 5]
a =
1 2 3 4
1 3 4 5
求和默认是列
>> sum(a)
ans =
2 5 7 9
>> sum(a,1)
ans =
2 5 7 9
求积
>> prod(a)
ans =
1 6 12 20
>> floor(a) %向下四舍五入
ans =
1 2 3 4
1 3 4 5
>> ceil(a) %向上四舍五入
ans =
1 2 3 4
1 3 4 5
>> max(rand(3),rand(3))
ans =
0.9572 0.2785 0.9649
0.6324 0.5469 0.9595
0.8003 0.9575 0.9706
>> A(:)
ans =
1
3
5
2
4
6
调换方向
>> flipud(eye(9))
ans =
0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 1 0
0 0 0 0 0 0 1 0 0
0 0 0 0 0 1 0 0 0
0 0 0 0 1 0 0 0 0
0 0 0 1 0 0 0 0 0
0 0 1 0 0 0 0 0 0
0 1 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0
求矩阵的拟
>> pinv(a)
ans =
1.3333 -1.0000
-1.6667 1.3333
-0.3333 0.3333
1.0000 -0.6667
>> D = [0:0.01:0.98]
>> y1 = sin(2*pi*4*D)
>> plot(D,y2,‘r‘)
>> xlabel(‘time‘)
>> ylabel(‘value‘)
>> legend(‘sin‘,‘cos‘)
>> title(‘my plot‘)
>> print -dpng ‘myplot.png‘
>> subplot(1,2,1)
>> plot(D,y1)
>> subplot(1,2,2)
>> plot(D,y2)
>> clf
>> A = magic(5)
A =
17 24 1 8 15
23 5 7 14 16
4 6 13 20 22
10 12 19 21 3
11 18 25 2 9
>> imagesc(A)
>> imagesc(A)
>> imagesc(A),colorbar,colormap gray
循环语句 判断语句
>> for i=1:10,
v(i)=2^(i);
end;
>> v
v =
2
4
8
16
32
64
128
256
512
1024
>> while true,
i =1;
v(i) = 100;
if i <=6,
break;
end;
end;
>> v
v =
100
4
8
16
32
64
128
256
512
1024
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