Today is the first day, I plan to finish this tutorial in two days

Interface knowledge

Command operation should be very familiar, it is similar to git or something

Editor: Click to create an editor to appear, the editor is mainly used for writing scripts

Notes

%%and%

Command Window Common Commands

clc - clears all commands in the command window

clear all - clears all variables in the workspace

Matlab variable naming rules

1. Case sensitive

2. The length is limited, 63 bits should not be too long

3. Variables start with a letter and can contain letters, underscores and numbers and cannot use punctuation

Matlab data types

numbers, characters and strings, matrices, cell arrays , structures

1. Numbers: + - */

2. String with single quotes ' '

        s= 'a'

        abs(s) %输出结果为数字

        char(97)  %97是阿斯克编码 输出结果为a

        num2str(65)  %把数字65转换为字符串‘65’

        length(str)  %字符串的长度

3. Matrix

Define the same row of the matrix with a space or comma to wrap the line with a semicolon

A=[1 2 3; 4 5 6; 7 8 9]   %定义一个矩阵

B=A'    %转置 行列对调

C=A(:)   %按列排列矩阵，将矩阵化为一列

D=inv(A)   %求逆  非方阵不能求逆

A*D   %矩阵相乘

E=zeros（10，5，3）   %10行5列3维 的全0矩阵

E(:,:,1)=rand(10,5)    %第一个维度  用10行5列的随机数填充

The difference between rand, randi, randn
rand(m,n) rand(m,n,'double') rand(RandStream,m,n)	1. Generate pseudo-random numbers of m rows and n columns The range of random numbers is 0~1 2. Generate uniform pseudo-random number parameters of specified precision with double and single 3. Use the specified random seed to generate pseudo-random numbers
randi(iMax） randi(iMax,m,n) randi([iMin,Imax],m,n)	1. Uniformly distributed pseudorandom integers in the open interval 0~imax'2. 2. Generating Matrix 3. The open interval becomes imin to imax
randn syntax is the same as rand	1. Generate a pseudo-random number with a standard normal distribution with a mean of 0 and a variance of 1.

4. Cell array

A cell array is a type of array, and its internal elements can be of different data types, very similar to the structure in c

A=cell(1,6) % 生成一个一行六列的元胞数组
A{2}=eye(3)  %eye矩阵就是E  赋值给元胞数组的第二个 cell 注意matlab的数据是从1开始的，而非0
A{5}=magic(5) %生成一个五阶的幻方 赋值给元胞数组的第五个cell
B=A{5}

MAGIC
magic（n）	1. The magic method is used in matlab to generate an n-order magic square. The n-order magic square refers to an N*N matrix, and the values of rows, columns or oblique additions are equal.

5. Structure

structure definition

books= struct('name',{
   
   {'machine learning','data minging'}},'price',[30,40])
books.name
books.name(1)
books.name{1}

Take a look at the running results

% Note that when books are defined, it is attribute name + attribute value, separated by commas

books =

A struct with the following fields:

name: {'machine learning' 'data minging'}
price: [30 40]

%books.name takes out the value of the property, which is a cell array
ans =

1×2 cell array

{'machine learning'} {'data minging'}

%books.name(1) is to take out the first cell of the cell array
ans =

1×1 cell array

{'machine learning'}

%books.name{1} takes a string, which is the value in the cell array
ans =

'machine learning'

I feel it can be understood as &a, &a[1], a[1]

Matrix Construction and Four Operations

1. Definition and Construction of Matrix

A=[1 2 3 4 5 6 7 8]

>> A=[1 2 3 4 5 6 7 8]

A =

1 2 3 4 5 6 7 8

B=1:2:9 % This is a sequence of starting values from left to right, and the maximum step size does not exceed

>> B=1:2:9

B =

1 3 5 7 9

C=repmat(B,3,2) % treat B as a whole and repeat three rows and two columns

>> C=repmat(B,3,2)

C =

1 3 5 7 9 1 3 5 7 9
1 3 5 7 9 1 3 5 7 9
1 3 5 7 9 1 3 5 7 9

D=ones(2,4) % generates a two rows and four columns while the values in the matrix are all 1

>> D=ones(2,4)

D =

1 1 1 1
1 1 1 1

2. Four operations on matrices

Matrix division:

(1) The right division formula A/B is equivalent to A*inv(B), that is, the inverse matrix of A right-multiplied by B;

(2) The left division formula A\B is equivalent to inv(A)*B, that is, the inverse matrix of A is left multiplied by B

X1=[7 5 3 ; 9 5 1]
X2=[4 5 6 ; 8 5 2]

X1 =

7 5 3
9 5 1

X2 =

4 5 6
8 5 2

X1+X2

years =

11 10 9
17 10 3

X1-X2

years =

3 0 -3
1 0 -1

X1*X2' % Note that the front row and back column should be the same

>> X1*X2'

years =

71 87
67 99

X1.*X2 % all plus. It means that the multiplication of the corresponding items is the number of the corresponding position of the front matrix and the back matrix.

>> X1.*X2

years =

28 25 18
72 25 2

X1./X2

>> X1./X2

years =

1.7500 1.0000 0.5000
1.1250 1.0000 0.5000

X1/X2 % does not need to be transposed here

>> X1/X2

years =

0.2500 0.7500
-0.2500 1.2500

3. The subscript of the matrix

A=magic(5) % First generate a 5*5 magic square matrix

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

A(2,3)

years =

7

A(3,:) % colon means all, take out all
ans in the third line =

4 6 13 20 22

[m,n]=find(A>20) The %find function means to find the coordinates in the matrix A that are greater than 20, because m is returned, and n is the form of a coordinate

m =

2
1
5
4
3

n =

1
2
3
4
5

MATLAB logic and flow control

1.if else end

2.for end

3.while end

4.switch case end

loop structure

for loop

for loop variable = initial value: step: end value

execute statement 1

execute statement n

end

The step size defaults to 1

For example, find the value of 1²+2²+...+5²

>>sum=0
>>for n=1:1：5
sum=sum+n^2;
end

ps: for loops can be nested

>>sum=0

>>for i=1:5

p=1

for j=1:i;

p=p*j;

sum=sum+p

end

while loop

In fact, it is similar to the language, while is followed by a conditional statement

>>s=0

>>n=1'

>>while n<=10

s=s+n

n=n+1

end

branch structure

if....end structure

if condition is true

execute conditional body

end exit the conditional body

>>a=100

>>b=20

>>if a>b

'established'

end

if..else..end statement body

>>a=100

>>b=20

>>if a>b

'established'

else

'invalid'

end

switch..case..end structure

switch expression (number or string)

case numeric or string

xxxx