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A picture is worth a thousand words, particularly visual representation of data in engineering is very useful. MATLAB has powerful graphics tools and there is a very helpful section devoted to graphics in MATLAB Help: Graphics. Students are encouraged to study that section; what follows is a brief summary of the main plotting features.
plot
StatementProbably the most common method for creating a plot is by issuing
plot(x, y)
statement where function y is plotted against x.
Type in the following statement at the MATLAB prompt:
x=[-pi:.1:pi]; y=sin(x); plot(x,y);
After we executed the statement above, a plot named Figure1 is generated:
Having variables assigned in the Workspace, x and y=sin(x) in our case, we can also select x and y, and right click on the selected variables. This opens a menu from which we choose plot(x,y). See the figure below.
Graphs without labels are incomplete and labeling elements such as plot title, labels for x and y axes, and legend should be included. Using up arrow, recall the statement above and add the annotation commands as shown below.
x=[-pi:.1:pi];y=sin(x);plot(x,y);title('Graph of y=sin(x)');xlabel('x');ylabel('sin(x)');grid on
Run the file and compare your result with the first one.
help gtext
help legendhelp zlabel
If you want to merge data from two graphs, rather than create a new graph from scratch, you can superimpose the two using a simple trick:
% This script generates sin(x) and cos(x) plot on the same graph
% initialize variablesx=[-pi:.1:pi]; %create a row vector from -pi to +pi with .1 incrementsy0=sin(x); %calculate sine value for each x
y1=cos(x); %calculate cosine value for each x% Plot sin(x) and cos(x) on the same graph
plot(x,y0,x,y1);title('Graph of sin(x) and cos(x)'); %Title of graph
xlabel('x'); %Label of x axisylabel('sin(x), cos(x)'); %Label of y axis
legend('sin(x)','cos(x)'); %Insert legend in the same order as y0 and y1 calculatedgrid on %Graph grid is turned
Multiple plots in a single figure can be generated with
subplot
in the Command Window. However, this time we will use the built-in Plot Tools. Before we initialize that tool set, let us create the necessary variables using the following script:
% This script generates sin(x) and cos(x) variables
clc %Clears command windowclear all %Clears the variable space
close all %Closes all figuresX1=[-2*pi:.1:2*pi]; %Creates a row vector from -2*pi to 2*pi with .1 incrementsY1=sin(X1); %Calculates sine value for each x
Y2=cos(X1); %Calculates cosine value for each xY3=Y1+Y2; %Calculates sin(x)+cos(x)
Y4=Y1-Y2; %Calculates sin(x)-cos(x)
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