As we all know, MATLAB is not only adept at handling numerical computations related to matrices, but it also has a deep foundation in scientific visualization. The many feature-rich functions it provides can very well meet our diverse needs for displaying numerical information graphically.
MATLAB has the capability to represent graphics in two dimensions, three dimensions, and even four dimensions. It can express data characteristics through aspects such as line style, boundary color, color, rendering, lighting, and perspective.
The visualization capabilities of MATLAB are built on a set of graphic objects. At the core of graphic objects is the operation of graphic handles (Graphics Handle).
Some commonly used low-level commands are as follows:
gcf: Returns the handle of the current window object (Get Current Figure)
gca: Returns the handle of the current axes object (Get Current Axes)
gco: Returns the handle of the current graphic object (Get Current Object)
get: Obtains the properties of the handle graphic object and returns certain object handle values
set: Changes the properties of the graphic object
This article mainly introduces some high-level plotting commands related functions:
x=0:0.01:2*pi;
y=cos(x);
plot(x,y);
xlabel(‘x-axis’); % x-axis annotation
ylabel(‘y-axis’); % y-axis annotation
title(‘Cosine Function’); % Graph title
legend(‘y = cos(x)’); % Graph annotation
gtext(‘y = cos(x)’); % Graph annotation, use mouse to position annotation
grid on; % Show grid lines
Create several coordinate systems on the same screen using the subplot(m,n,p) command;
Divide one screen into m×n graphic areas, where p represents the current area number, and draw a graph in each area.
x=linspace(0,2*pi,30);y=sin(x); z=cos(x);
u=2*sin(x).*cos(x);v=sin(x)./cos(x);
subplot(2,2,1),plot(x,y),axis([0 2*pi -1 1]),title(‘sin(x)’)
subplot(2,2,2),plot(x,z),axis([0 2*pi -1 1]),title(‘cos(x)’)
subplot(2,2,3),plot(x,u),axis([0 2*pi -1 1]),title(‘2sin(x)cos(x)’)
subplot(2,2,4),plot(x,v),axis([0 2*pi -20 20]),title(‘sin(x)/cos(x)’)
For 3D plotting in MATLAB, the most commonly used functions are surf and mesh, along with their derived functions.
x=linspace(-2,2, 25); % Take 25 points on the x-axis y=linspace(-2, 2, 25); % Take 25 points on the y-axis [xx,yy]=meshgrid(x, y); % xx and yy are both 21×21 matrices zz=xx.*exp(-xx.^2-yy.^2); % Calculate function values, zz is also a 21×21 matrix surf(xx, yy, zz); % Draw the 3D surface plot
Using the peaks function as an example, plot in various ways 1. meshz can add a skirt to the surface: [x,y,z]=peaks;meshz(x,y,z);axis([-inf inf -inf inf -inf inf]);
2. waterfall can create a water flow effect in the x or y direction:[x,y,z]=peaks;waterfall(x,y,z);axis([-inf inf -inf inf -inf inf]);
3. Water flow effect in the y direction:[x,y,z]=peaks;waterfall(x’,y’,z’);axis([-inf inf -inf inf -inf inf]);
4. meshc can simultaneously draw a mesh graph and contour lines: [x,y,z]=peaks;meshc(x,y,z);axis([-inf inf -inf inf -inf inf]);
5. surfc can simultaneously draw a surface plot and contour lines:[x,y,z]=peaks;surfc(x,y,z);axis([-inf inf -inf inf -inf inf]);
6. Comparing the functions meshc, meshz, surfc, and surfl
[x,y]=meshgrid(0:0.1:2,1:0.1:3)
z=(x-1).^2+(y-2).^2-1
subplot(2,2,1);meshc(x,y,z)
subplot(2,2,2);meshz(x,y,z)
subplot(2,2,3);surfc(x,y,z)
subplot(2,2,4);surfl(x,y,z)
For example, using the same color map, draw a cone using different coloring methods.
[x,y,z] =cylinder(pi:-pi/5:0,10)
colormap(lines)
subplot(1,3,1)
surf(x,y,z);
shading flat
subplot(1,3,2)
surf(x,y,z);
shading interp
subplot(1,3,3)
surf(x,y,z)
Author: Senior Zhang from Extreme Value Academy
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