In the SMDm-file, insert a figure command before the second plot command:
45   end
46   figure
47   plot(t,y2,’LineWidth’,3,’LineStyle’,...
48   ’—’,’Color’,’Blue’);
Save and run the m-file.
There will be two graphs created in windows labeled Figure 1 and Figure 2.
While this example showed how to create multiple graphs from an m-file, we
want to show both sets of data on a single graph. For this, we will need to use the
hold command. The hold oncommand keeps the current graph open so that sub-sequent plotting commands will add to the current graph. There is also a  hold off
command that closes the graph from further additions. The use of the  hold com-mand alone (without the value in parentheses) toggles the command between
hold onand  hold off. To prevent ambiguity, it is recommended that  onor offbe
specified.
Since we will have more than one curve on the graph, we will need a legend to
distinguish them.
In the SMDfile, replace the figure command with a hold oncommand. Also,
add thelegend command as shown:
45   end
46   hold on
47   plot(t,y2,’LineWidth’,3,’LineStyle’,...
48   ’—’,’Color’,’Blue’);
49   legend(‘Damping Coefficient = 0.1’,...
50   ‘Damping Coefficient = 0.2’);
Note that in the legend command, the two curves are identified in the order in
which they are created.
Save and run the file. Make any desired edits (such as the font sizes of the leg-end and numbers on the axes) to the graph with the Property Editor. Click and
drag the legend to the desired location.
166 CHAPTER 5 Plotting Data
The finished graph is shown in Figure 5.60.
Another useful MATLAB plotting command is  fplot. To use  fplot, the function to
be plotted must be written as a MATLAB function m-file. The general form of
the  fplot command is as follows:
fplot(‘functionname’,[x
lower
x
upper
])
where x
lower
and x
upper
are the lower and upper limits of the function arguments.
That is, x
lower
and x
upper
define the domain of the independent variable. The  fplot
command can be used to plot built-in MATLAB functions in addition to function
files that you generate. For example, we can plot the  sin function for values of
zero to 2 π radians by entering this command:
>> fplot(‘sin’,[0 2*pi])
To plot the displacement of our spring-mass-damper system, we must first create
a function file.