Summary of MATLAB basic grammar

1. Interface understanding

• Command line input clc： Clear the command line window
• Command line input clear all: Clear the right workspace
• %： Comment code

2. Variable naming

• Case sensitive
• Start with a letter , You can use underscores

3. data type

• Numbers ：abs()
• Characters and strings ： String in single quotes 、char()、length()
• matrix

A=[1 2 3; 4 5 6; 7 8 9]
B=A' %  Transposition 
C=A(:) %  Vertical stretching 
D=inv(A) %  Seeking inverse 
A*D

E=zeros(10,5,3) % 10 That's ok 5 Column 3 dimension 
E1=rand(10,5) % 0-1 A pseudo-random number uniformly distributed between 
E2=randi([3,7],10,5) %  A fixed range of random integers 
E3=randn(10,5) %  Pseudorandom number of standard normal distribution （ The mean for 0, The variance of 1）

• Cell array

A=cell(1,6) % 1 That's ok 6 A cellular array of columns 
A{
    2}=eye(3) % 3 That's ok 3 Unit matrix of columns 
A{
    5}=magic(4) % 4 Step magic square 

• Structure

books=struct('name',{
    {
    'Machine Learning','Data Mining'}},'price',[30,40])
books.name
books.name(1) % 1×1cell
books.name{
    1} %  character string 

4. Matrix construction and four operations

• Matrix construction

A=[1 2 3 4 5 6]
B=1:2:9 %  The scope is 1-9, In steps of 2
C=repmat(B,3,2) %  Give Way B Matrix repetition 3×2 Time 
D=ones(4,4) %  Generate 1 individual 4×4 Of all the 1 matrix 

application ：

Solve a system of linear equations ：

A=[5 6 -12; 6 5 -2; 4 -9 2;]
B=[1 129 17]'
invA=inv(A)
X=invA*B

• arithmetic

A=[1 2 3 4; 5 6 7 8]
B=[4 3 2 1; 8 7 6 5]
C=A+B
D=A-B
E=A*B' %  matrix multiplication ,A The line of =B The column of 
F=A.*B %  Multiply the corresponding terms 
G=A/B % G*B=A 
H=A./B %  The corresponding term is divided by 

• The subscript of a matrix

A=magic(5)
B=A(2,3) %  take A Matrix No 2 Xing di 3 Number of columns 
C=A(3,:) %  take A The order of the matrix 3 That's ok 
D=A(:,4) %  take A The order of the matrix 4 Column 
[m,n]=find(A>15) %  find A Greater than in matrix 15 Number of numbers , And expressed by subscript 

5. Program structure

• for

%  seek 1-5 The sum of the squares 
sum=0;
for i=1:5
    sum=sum+i^2;
end

• if

a=100;
b=20;
if a>b
    ' establish '
else
    ' Don't set up '
end

• while

%  seek 1-10 And 
sum=0;
n=1;
while n<=10
    sum=sum+n;
    n=n+1;
end

6. 2D plane drawing

Example 1：

x=0:0.01:2*pi;
y=sin(x);
figure %  Curtain 
plot(x,y)
title('y=sin(x)')
xlabel('x')
ylabel('sin(x)')
xlim([0 2*pi])

Example 2：

x=linspace(0,30,500); % 0-30 Between 500 Elements 
y=x.*sin(x); %  Gain sine function 
plot(x,y,'LineWidth',1.5); %  The line width is 1.5
title(' Gain sine function ');
xlabel('\alpha');
ylabel('sin(\alpha)');
legend('sin(\alpha)'); %  Insert line callout 
text(2,2*sin(2),'\rightarrow Okey!'); %  Insert text and arrows 
grid on; %  Show gridlines 
box on; %  Show axis box 

Example 3：

x1=linspace(0,2*pi,100);
x2=linspace(0,3,100);
y1=1/3*x1.*sin(2*x1);
y2=x2.^2+2*x2;
plot(x1,y1,'r:',x2,y2,'b--');

Example 4：

x=linspace(0,2*pi,60);

subplot(2,2,1);
plot(x,sin(x)-1);
title('sin(x)-1');
axis([0,2*pi,-2,0]);

subplot(2,1,2);
plot(x,cos(x)+1);
title('cos(x)+1');
axis([0,2*pi,0,2]);

subplot(4,4,3);
plot(x,tan(x));
title('tan(x)');
axis([0,2*pi,-40,40]);

subplot(4,4,8);
plot(x,cot(x));
title('cot(x)');
axis([0,2*pi,-35,35]);

7. Three dimensional drawing

Example 1：

x=0:pi/50:10*pi;
plot3(sin(x),cos(x),x);
xlabel('sin(x)');
ylabel('cos(x)');
zlabel('t');
grid on;
axis square; %  Set the current coordinate system drawing to square 

Example 2：

[x,y,z]=peaks(30);
mesh(x,y,z);
grid on;