Matlab

Matlab Predefined variables in

• ans: The variable name of the preset calculation result
• eps:Matlab Defined positive minima = 2.2204e^(-16)
• pi: 3.14xxxxxxxxxxxxxx
• inf: infinity
• NaN: Cannot define
• i or j: An imaginary unit
• ....

Matlab assignment

Matlab Assignment in , You can not define variables first or use variables directly

5+6
ans = 11

a = 5;
b = 6;
a+b
ans = 11

The effect is the same , The key is the matrix ,

y = [1 2 3 4]; % Row vector 
y = [6:7:8:9]; % Column vector 
y' % Transposition 

Matlab arithmetic

Matlab Addition, subtraction, multiplication, division and C The addition, subtraction, multiplication and division of language is no different from the use of ordinary numbers , Such as ：
ans1 = a+b;
ans2 = a*b;
ans3 = a-b;
ans4 = a/b;

Max min function

• max
• min’

max(x)              % Output vector X Maximum of 
[Y,I] = max(X)      % Output vector X The maximum value and its Y The serial number of I

min(W)		         % Output vector W Minimum of 
[Z,J] = min(w)       % Output vector W Minimum of Z And its Z The serial number of J

What is a vector （vector）

Definition ： A quantity that has both direction and size is called a vector （ Contains a variety of information / The amount of multiple elements ）

Build a vector

1、 Direct input method
Such as ：

x=[1,2,3,4,5]

or

x=[1 2 3 4 5]

2、 Command format

x_star : x_add：x_end

• x_star Starting value
• x_add Incremental value
• x_end End value

（ The default increment is 1）
Such as ：

x = 1:5

The result is

x = 1 2 3 4 5

3、 Linear bisection method

linspace(int_start,int_end,n)

• int_start % The starting value of the bisection interval
• int_end % The end value of the bisection interval
• n % Divide the number equally

Vector length

In vector calculation , We must pay attention to the consistency of vector length .
command ：

length(x)

Such as ：

x=[1 2 3 4 4];
length(x)

Results show

ans = 8

The addition of vectors / Subtraction

Such as ：

A = [1 2 3];
B = [4 5 6];
sum = A+B
diff = A-B

The result is ：

sum = 5 7 9
diff = -3 -3 -3

The multiplication of vectors / division

Multiplication and division of vectors or matrices 、 power 、 Square root operation , You need to add... Before the operator “.”
Such as ：

A = [1 2 3];
B = [4 5 6];
P = A.*B
Q = A./B

Power of vector （power）

"^" stay matlab Represents the caret

A = [1 2 3];
A_POWER = A.^4

The square of the vector （square root）

There is no square symbol directly on the keyboard , So change your mind , Replace the square with a power to do .
namely ：
Radical sign a = a.^(1/2), And so on . Of course , Square can be used directly sqrt(x), The others can be directly made into the form of power .