Graphic drawing in MATLAB

MATLAB Graphics are usually drawn by tracing points 、 The way of connection . The graphic drawing is realized by providing the point coordinates of key positions and the specific link between points .

At the same time, it supports drawing multiple graphics on the same picture , In order to distinguish different graphics , Available in different colors 、 size 、 Shape and link mode to distinguish different graphics .

Drawing of two-dimensional graphics

because MATLAB The figure is drawn by tracing points 、 Connected to achieve , Therefore, when drawing simple plane graphics, it is necessary to provide the horizontal and vertical coordinates of a series of points on the graphics , Then link these points . The specific graphic drawing command is ：

  plot(X,Y,’S’)

among X,Y It's a vector , They are vectors composed of abscissa and ordinate of all points ,S It's a string , Used to determine the color of the line , The drawing shape of points and the link mode between points .

matlab Implicit function drawing by entering... In the command window help plot Commands can be viewed S Specific writing method of .Y Sometimes it can be a matrix , At that time, multiple curves will be drawn for the same independent variable .

example

With vectors y=(1,2,5,4.5,3,6,1) The components of are ordinates , The component serial number is the abscissa drawing sequence connecting line .

Explain ： Enter the command

y=1 2 5 4.5 3 6 1;

plot(y)

example

Draw a sine curve and a cosine curve .

 >>x=0:pi/10:2*pi;   % Construct vectors

       >>y1=sin(x);           % The structure corresponds to y1 coordinate

       >>y2=cos(x);          % The structure corresponds to y2 coordinate

       >>plot(x,y1,x,y2)    % Draw a picture to x Abscissa ,y1,y2 Figure with vertical coordinates  

Be careful

① The so-called colon method is used to construct the vector , The format is

Vector name ＝ initial value : step ： Final value   % In steps of 1 You can omit .

②plot Is to draw a curve for the column of a vector or matrix , in other words , Use plot You must first define the of each point on the curve x Coordinates and y coordinate .

③ In the above format ,x and y Can be expressions .

④ If the interval between independent variables is large , The smooth curve will show the original appearance of the polyline .

example

matlab Beginner's course students with excellent grades in a certain exam account for 8%, Good accounting for 20%, Medium accounts for 36%, Those who pass account for 24%, Those who fail account for 12%. It is represented by pie chart and bar chart respectively .

Explain ：

x=8 20 36 24 12;

subplot(221);pie(x,1 0 0 0 1);

title(' The pie chart ');

subplot(222);bar(x,'grpup');

title(' Vertical bar chart ');

subplot(223);bar(x,'stack');

title(' Vertical bar chart whose cumulative value is ordinate ');

subplot(224);barh(x,'group');

title(' Horizontal Bar Graph ');

About curve control commands   

In the use of plot You can specify the color of the curve when drawing the curve with the command 、 Linetype and data point icons . The basic call format is

plot(x,y,'color line-style marker')

Be careful

① Color 、 Linetype 、 The symbols marking the three attributes must be placed in the same string .

② The order of attributes doesn't matter , You can specify only one or two properties , You can also default to all , But the same attribute cannot specify two at the same time .

③ The default color is blue .

④ spot 、 The line identifier defaults to solid line .

⑤ There is no interval between attributes .

example

In red 、 Point connection 、 Cross to draw a sine curve .

 >>x=0:0.2:8;

           >>y=sin(x);

           >>plot(x,y,'r:x')

About drawing annotation commands

example

Add grids and labels to the graphics of the above example .

 >>x=0:pi/10:2*pi;   

       >>y1=sin(x);        

       >>y2=cos(x);        

       >>plot(x,y1,x,y2)   

       >>grid on                              % Adding grid

       >>xlabel(‘x Axis ’)                       % Cross sitting label

       >>ylabel(‘y Axis ’)                       % Ordinate name

       >>title(‘ Sine and cosine function curves ’)   % title

       >>text(1.5,0.3,’cos(x)’)   % Specify the location dimension

       >>gtext(‘sin(x)’)     % Use the mouse to select the position label

       >>axis(0 2*pi -1.2 1.2 % Set the maximum and minimum value of the coordinate axis

hold on(/off) Keep drawing commands

subplot(n,m,k) Divide the graphics window into n That's ok m Make a grid , In the k A grid drawing , The grid is counted in rows from top to bottom .

example

In the same window , Use twice plot function , Draw two curves .

   >>x=0:0.2:12;

         >>plot(x,sin(x),’-’)

         >>hold on

         >>plot(x,cos(x),’:’)

example

Divide the current window into four areas , Draw four function curves .

   >>x=0:0.05:8;

                 >>y1=2*sin(x);

                 >>y2=2*cos(x);

                 >>y3=sin(2*x);

                 >>y4=cos(2*x);

                 >>subplot(2,2,1);

                 >>plot(x,y1);

                 >>title(‘2sinx’)

                 >>subplot(2,2,2);

                 >>plot(x,y2);

                 >>title(‘2cosx’)

                 >>subplot(2,2,3);

                 >>plot(x,y3);

                 >>title(‘sin2x’)

                 >>subplot(2,2,4);

                 >>plot(x,y4);

                 >>title(‘cos2x’)

Drawing of three-dimensional graphics

stay MATLAB The command for drawing 3D curves in is

  plot3(x,y,z,’S’)

among x,y,z They are the horizontal of points 、 Vertical and vertical coordinates ,S For the string ,matlab Four dimensional graph Similar to the drawing string of two-dimensional graphics .

stay MATLAB Draw three-dimensional arrow function in

  quiver3(x,y,z,u,v,w)

example  

Trial drawing

The graphic .

Explain  

Enter the following commands in the command window , The figure shown in the figure can be obtained .

t=0:0.01:10*pi;

x=sin(t);

y=cos(t);

plot3(x,y,t,'g');

The commands for drawing 3D surfaces are  mesh(x,y,z) or surf(x,y,z).  The difference is , The former draws a surface approximated by a mesh , The latter draws a true surface .

example

Draw a multimodal function diagram .

   >>z=peaks(40);

       >>mesh(z);

       >>surf(z);

peaks It is called multimodal function , Commonly used for the demonstration of 3D surfaces . 

example  

Trial drawing z=x²-y² The graphic .

Explain  

First, take the horizontal and vertical coordinates , Enter the following command

x=-10:0.5:10;

y=-10:0.5:10;

Second, use meshgrid Command to generate horizontal and vertical cross grid coordinates , The specific command is as follows ：

xx,yy=meshgrid(x,y)

Finally, generate vertical coordinates and draw . The specific command is as follows ：

z=xx.^2-yy.^2;

mesh(xx,yy,z);

  Decoration of graphics

(1) Coordinate axis and drawing name

The following commands can be used to name the coordinate axis and graphics

xlabel(‘ Specific name ’)

ylabel(‘ Specific name ’)

zlabel(‘ Specific name ’)

title (‘ Specific name ’)

(2) Add grid

adopt grid on or grid off Command to add grid or delete grid .

(3) Add embellishment to the graph

In order to add text to the graphics to realize the decoration of the graphics , It can be done by gtext(‘string’) To achieve the decoration of graphics . When running gtext On command , A cross will appear on the screen , Move the cross to the specified position and press the left key , The marked string will be placed in this position .