[matlab] 2D drawing summary

Reference material ：
《Matlab Programming and its application Lecture 3 》—— Lu Wei
《Matlab Help document 》

1. Basic drawing functions ：plot function .

2. function ： Yes $x$ Coordinates and corresponding $y$ Coordinate drawing .

3. plot Function usage format ：

   plot(x, y, ...);

notes ： The ellipsis part can supplement the nature of the figure , And then we'll talk about .

4. The function pair $x$ and $y$ There are certain requirements for the form of , If the requirements are not met, an error will be reported , The form meeting the requirements is shown in the table below .

$x$ Possible forms	$y$ Possible forms	The effect of drawing
$1\times n$ Matrix	$1\times n$ Matrix	Yes $y$ mapping
$1\times n$ Matrix	$m\times n$ Matrix	use $x$ And $y$ Each line vector plot of
$m\times n$ Matrix	$m\times n$ Matrix	use $x$ Each row vector of is associated with $y$ Plot the corresponding line vector

Special use forms ： Just give $y$, Don't give $x$ :

	plot(y, ...);

At this time , It will put $y$ The matrix formed by the index of is regarded as $x$ Draw .

5. Change line properties

（1） Linetype ( $LineStyle$ )、 Point type ( $Marker$ ) And color （$Color$）

Let's start with an example ：

	clear; clc;
	close all;
	t = 0 : pi/10 : 2*pi;
	x = t - 3;
	y = sin(t);
	z = cos(t);
	plot(t, x, '-r'); hold on;
	plot(t, y, '--g');
	plot(t, z, '*b');
	% The above two lines can also be written in one line : plot(t, x, '-r', t, y, '--g', t, z, '*b');

The result of the drawing ：

• Linetype

plot Functional Line Style	explain
-	Solid line （ The default value is ）
- -	Dotted line
:	Dotted line
-.	Dotted line

• Point type

plot Functional Marker	explain
O	circular
+	plus
X	Cross
*	asterisk
.	Order number
^	Triangle up
V	Triangle down

• Color

plot Functional Color	Color effect	RGB value
b	Blue (Blue)	(0,0,1)
c	Blue (Cyan)	(0,1,1)
g	green (Green)	(0,1,0)
k	black (Black)	(0,0,0)
m	Purple black (Magenta)	(1,0,1)
r	Red (Red)	(1,0,0)
w	white (White)	(1,1,1)
y	Yellow (Yellow)	(1,1,0)

Modify Linetype 、 Dot type or color , Directly in $x,y$ Add later （ Separated by commas ） Corresponding marks （ Enclose in single quotation marks ） That's all right. , Here are some examples ：

	% Linetype 
	plot(x, y, '--k');
	plot(x, y, 'b:');
	plot(x, y, '-.c');
	% Point type 
	plot(x, y, 'Xm');
	plot(x, y, 'y*');
	plot(x, y, '+g');
	% Set both line type and point type 
	plot(x, y, '*-r');
	plot(x, y, '^--g');

notes ： Color marks and lines （ spot ） The position of the mark of the model can be changed , Anyone who is in the front can . You can also set the linetype and point type at the same time .

(2) Line width （$LineWidth$）

Direct example ：

	% The default line width is  0.5
	plot(x, y, '--r', 'LineWidth', 2);
	plot(x, y, '-.g', 'LineWidth', 0.3);

These are the commonly used properties , If you want to realize some special needs , You can refer to Matlab Help document .

6. Add explanatory text

To enhance the readability of graphics , It is often necessary to add descriptive text to the graph or coordinate axis .

Instructions	explain
title	The title of the figure
xlabel	$x$ Description of the shaft
ylabel	$y$ Description of the shaft
legend	Annotation legend
text	Add text to the drawing
gtext	Use the mouse to position the text

notes ： commonly $legend$ At the end , Draw some pictures in front ,$legend$ A few legends are added in .
Example ：

	clear; clc;
	close all;
	t = 0 : pi/10 : 2*pi;
	x = t - 3;
	y = sin(t);
	z = cos(t);
	plot(t, x, '-r', t, y, '--g', t, z, '*b');
	xlabel('t = 0 to 2\pi'); 
	ylabel('values of t - 3, sin(t) and cos(t)');
	title('Function Plots of t - 3, sin(t) and cos(t)');
	% stay （3,3） Add text with blue font color at 
	text(3, 3, ' The added text is here ', 'Color', 'b');
	% Here, in order not to block the figure , Place the legend in 'northwest' It's about , That's the upper left corner , The default is the upper right corner 
	legend({'t - 3', 'sin(t)','cos(t)'}, 'location', 'northwest');
	shg; % Display images 

The result of the drawing ：

notes ： You can use... In text Latex The grammar of .

7. Change axis properties

The most common is axis Instructions , Common functions are listed as follows ：

	clear; clc;
	close all;
	t = 0 : pi/10 : 2*pi;
	y = sin(t);
	plot(t, y);
	x1 = 0;
	x2 = 6;
	y1 = -3;
	y2 = 3;
	axis([x1 x2 y1 y2]); % Set up x Axis range is  x1  To  x2, y Axis range is  y1  To  y2;
	shg;pause(2);
	% Other common functions are as follows ：
	axis xy; %xy-Default Direction . about 2d Axis in view ,y The axis is vertical , The value is incremented from bottom to top 
	shg;pause(2);
	axis ij; %ij-Reverse Direction . about 2d Axis in view ,y The axis is vertical , The value is incremented from top to bottom 
	shg;pause(2);
	axis auto; % Automatically generate coordinate axis range 
	shg;pause(2);
	axis padded; % Fill the margin between the graph and the drawing box 
	shg;pause(2);
	axis tight; % Set the axis limit equal to the range of the data , So that the drawing extends to the edge of the axis 
	shg;pause(2);
	axis equal; % Set the unit length of each coordinate axis to be equal 
	shg;pause(2);
	axis off; % Hide axis 
	shg;pause(2);
	% notes ： The above commands can be superimposed , Like the following example ：
	axis equal tight;

8. Some other functions

（1）hold function

This function has been used in the previous example , Its function is to continue adding curves to the graph that has been drawn .

	clear; clc;
	close all;
	t = 0 : pi/10 : 2*pi;
	x = t - 3;
	y = sin(t);
	plot(t, x);
	shg;
	
	% If you do not add this statement here , Then the figure above will disappear , It is covered by the following figure 
	hold on;
	
	plot(t, y);
	shg;
	% If you want to redraw , I don't want to add graphics to the original diagram , Use hold off;
	hold off;
	z = cos(t);
	plot(t, z);
	shg;

（2）grid function

Sometimes you want to add a grid to the graph , So as to better observe the change of waveform , Then you can use grid on Instructions , If you want to close the grid , Reuse grid off Command can .
Example ：

	clear; clc;
	close all;
	t = 0 : pi/10 : 2*pi;
	y = cos(t);
	plot(t, y);
	grid on; % Show gridlines 
	shg;
	grid minor; % Use this command to display primary and secondary gridlines 
	shg;
	grid off; % Turn off gridlines 
	shg;

（3）plotyy function

Draw two curves with different ranges in the same window , Use different y Axis scale .
Such as ：

	x = 0:0.01:20;
	y1 = 200*exp(-0.05*x).*sin(x); % Point multiplication is the multiplication of each element of two matrices 
	y2 = 0.8*exp(-0.5*x).*sin(10*x);
	plotyy(x, y1, x, y2, 'plot');

The effect is shown in the figure below ：

（4）subplot function

Use instruction subplot(m, n, p) Windows can be divided into $m\times n$ Sub window , next plot The instructions are plotted on $p$ Sub window .$p$ The counting method of is left to right , Count from top to bottom , from 1 Start .
Examples are as follows ：

	x = 0:pi/30:2*pi;
	subplot(2, 2, 1); % top left corner 
	plot(x, sin(x));
	title('sin(x)');
	
	subplot(2, 2, 2); % Upper right corner 
	plot(x, cos(x));
	title('cos(x)');
	
	subplot(2, 2, 3); % The lower left corner 
	plot(x, exp(-x).*sin(3*x));
	title('e^{-x} \cdot sin(3*x)'); % It's used here Latex grammar ：\cdot（ Point multiplication ）
	
	subplot(2, 2, 4); % The lower right corner 
	plot(x, x.^2);
	title('x^2');

The result is as follows ：

notes ： Use subplot() You can also combine sub windows , For example, command subplot(2, 2, [1, 3]) Will be 1 Window No. 1 and 3 No. 1 window combined , next plot The instruction is to draw in the combined window , No more examples .

（5） Draw plural numbers

z Is a complex vector , So order plot(z) Is equivalent to plot(real(z), imag(z)), the z The real part and the imaginary part of are regarded as x Coordinates and y Drawing with coordinates .
Examples are as follows ：

	theta = pi/2 : 2*pi/5 :(2*pi+pi/2);
	z = exp(j*theta);
	colordef black;// Set the background color to black 
	plot(z);
	
	% Make the unit length of horizontal and vertical coordinates equal , At the same time, the range of horizontal and vertical coordinates is just equal to the range of data 
	axis equal tight;
	
	axis off;% Hide axis 

The final effect is as follows ：

8. At the end

If there is any mistake, please point it out , Learning together , Common progress ！
If there are any questions , Welcome to ask questions ！
thank you ！

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