This document discusses MATLAB graphics and plotting discrete and continuous signals. It provides examples of plotting single and multiple signals, changing plot settings, using subplots, generating sine waves, and tasks for practicing MATLAB plotting. Key topics covered include using stem, plot, and hold on to display signals; setting line types and styles; manually zooming axes; creating subplots; and generating and playing sine waves with MATLAB.

1. Lab No.04
MATLAB graphics
Designed by : Dawar Awan
dawar@cecos.edu.pk
CECOS College of Engineering and IT
March – July 2012

2. Discrete signals
 Plot the discrete signal x = [1 2 3 4] in MATLAB
4
3
2
1
-1
0
1
2
 using stem(x) plots the signal starting from index number 1
CECOS College of Engineering and IT
March – July 2012

3. Practice
 Plot the following discrete time sequences
x[n]=[1 1 1 1 2 1 1 1 1]
x[n]=[5 4 3 2 1 0 1 2 3 4 5]
CECOS College of Engineering and IT
March – July 2012

4. Continuous plot
 >> plot(n,x)
 Shows a continuous plot of x
 Actually the discrete points are only connected with
straight lines.
CECOS College of Engineering and IT
March – July 2012

5. Labeling the plot
 Example:
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March – July 2012

6. Labeling the plot
CECOS College of Engineering and IT
March – July 2012

7. Multiple plots
 Using single “plot” instruction
 Example:
x = 0:0.01:5;
y1=sin(x);
y2=sin(2*x);
y3=sin(4*x);
plot(x,y1,x,y2,x,y3)
CECOS College of Engineering and IT
March – July 2012

8. Multiple plots
CECOS College of Engineering and IT
March – July 2012

9. Multiple plots
 Using multiple “plot” instructions
 Example:
x = 0:0.01:5;
y1=sin(x);
y2=sin(2*x);
y3=sin(4*x);
plot(x,y1);
hold on;
plot(x,y2);
plot(x,y3);
CECOS College of Engineering and IT
March – July 2012

10. Multiple plots
CECOS College of Engineering and IT
March – July 2012

11. Changing default plot settings
 Example:
x = 0:0.1:5;
y1=sin(x);
y2=sin(2*x);
y3=sin(4*x);
plot(x,y1,’+’,x,y2,':',x,y3,‘--');
CECOS College of Engineering and IT
March – July 2012

12. Changing default plot settings
CECOS College of Engineering and IT
March – July 2012

13. Changing default plot settings
 line types and mark types
Linetypes :
solid (-), dashed (--), dotted (:), dashdot (-.)
Marktypes :
point (.), plus (+), star (*), circle (o), x-mark (x)
Check the help of “plot” for more effects.
CECOS College of Engineering and IT
March – July 2012

14. Axis command
 Used to manually zoom axis
 axis([xmin xmax ymin ymax])
 Example:
CECOS College of Engineering and IT
March – July 2012

15. Axis command
 Without axis command
CECOS College of Engineering and IT
March – July 2012

16. Axis command
 With axis command
CECOS College of Engineering and IT
March – July 2012

17. SUBPLOT
 Example:
x = 0:1:10;
y = x.^2;
z = 10*x;
subplot (1,2,1)
plot(x,y)
subplot (1,2,2)
plot(x,z)
subplot(m,n,p) : makes m rows and n columns of figures in figure window
and p shows the location of the current plot i.e the plot instruction just below
the subplot
CECOS College of Engineering and IT
March – July 2012

18. SUBPLOT
CECOS College of Engineering and IT
March – July 2012

19. Generating a sine wave
 Example: creating a 5Hz sine wave, sampled at 8000Hz.
f=5;
fs=8000;
t=[0:1/fs:1];
y=sin(2*pi*f*t);
plot(t,y);
CECOS College of Engineering and IT
March – July 2012

20. Generating a sine wave
 Observe 5 cycles per second.
CECOS College of Engineering and IT
March – July 2012

21. Generating a sine wave
 Example: Creating a 1000Hz sine wave, sampled at
8000Hz, and routing it to computer’s soundcard.
f=1000;
fs=8000;
t=[0:1/fs:3];
y=sin(2*pi*f*t);
sound(y,fs);
The sound will be heard for 3 seconds, as dictated by the code
CECOS College of Engineering and IT
March – July 2012

22. Task
1. Plot the two curves y1 = x2 and y2 = 2x on the same graph using
different plot styles. Label the plot properly
2. Write a MATLAB program that adds the following two signals,
Plot the original signals as well as their sum.
x1[n] = [2 2 2 2 2]
x2[n] = [2 2 2 2 0 0]
3. Scale the amplitude of the following signal by a factor of 2 and
½ and show the scaled signals along with the original.
x(t) = sin(t) + 1/3sin(3t)
CECOS College of Engineering and IT
,
t=0:0.01:10
March – July 2012

23. Tasks
4. Demonstrate the use of the function ”plot3” to plot a straight
3D line
CECOS College of Engineering and IT
March – July 2012