1. MatLab – Palm Chapter 5 2-D & 3-D Plots
Class 13.1
Palm Chapter: & 5.8
9/20/2018
ENGR 111A Fall 2004

2. RAT 13.1
As in INDIVIDUAL you have 2 minutes to answer the following question.
What is the result of the following subplot and plot commands: x = [0:5];
y = x.^2;
subplot(2,2,4)
plot(x,y)
Answer:
Creates a plot of y vs. x on a figure window with four “panes”. This plot would be in the lower, right pane of the figure window.
9/20/2018
ENGR 111A Fall 2004

3. Solution
9/20/2018
ENGR 111A Fall 2004

4. Learning Objectives for Today’s Class
Students should be able to:
Use the 2-D (X-Y) Plotting Functions.
Make Subplots and Overlay Plots.
Use Special Plot Functions.
Use the Plot Editor.
Use the 3-D (X-Y-Z) Plot Functions.
9/20/2018
ENGR 111A Fall 2004

5. Good Plotting Practices
Each axis must be labeled with the name of quantity plotted and units
Axes should have tick marks at regular, convenient intervals
Label multiple lines or include legend
Use a title if needed
Plot each measured data point with a symbol
Use lines between data points to improve readability, but with caution
Do not plot points if the curve is generated from a continuous function
All fonts must be 8pt or greater at the final printed size
GOOD NEWS: Matlab does most of this automatically!
9/20/2018
ENGR 111A Fall 2004

6. Example Plots Matlab Default Mixed fonts Plot markers on curve Smaller
fonts, but
uniform
size
9/20/2018
ENGR 111A Fall 2004

7. Important Plot Commands
plot(xdata,ydata,’csl’,’prop1’,val1,…)
grid on; grid off
title(‘Put title here’)
xlabel(‘Use ^ for superscripts’)
ylabel(‘Use _ for subscripts’)
legend(‘Line 1’, ‘Line 2’, …)
axis – lots of variants.
axis square, axis equal, axis auto
axis([xmin, xmax, ymin, ymax])
See online
HELP
9/20/2018
ENGR 111A Fall 2004

8. In-Class Exercise 13.1-1 (10-min)
Individually solve T5.1-1
A. First, using plot() commands.
B. Using fplot() (see page 266).
Remember to label axes, pay attention to fonts, etc.
Experiment with various axis and grid commands.
Also try semilogy(), semilogx(), and loglog()instead of plot()
9/20/2018
ENGR 111A Fall 2004

9. Solution using plot() x = 0:0.1:35; y = 0.4*sqrt(1.8*x);
plot(x, y, ‘r-’)
axis([ ])
title(‘Rocket trajectory’)
xlabel(‘Distance [miles]’)
ylabel(‘Height [miles]’)
grid on
9/20/2018
ENGR 111A Fall 2004

10. Solution
9/20/2018
ENGR 111A Fall 2004

11. Solution using fplot()
f = ‘0.4 * sqrt(1.8*x)’
fplot(f, [0 35])
axis([ ])
title(‘Rocket trajectory’)
xlabel(‘Distance [miles]’)
ylabel(‘Height [miles]’)
grid on
9/20/2018
ENGR 111A Fall 2004

12. 5.2 Subplots and Overlay Plots (p. 271)
subplot(rows, cols, plot_num)
hold on; hold off
text(xpos, ypos, ‘text label’)
print fname.ps % creates % postscript file
Also use edit-copy figure
Beware that what you see is not necessarily what you get
9/20/2018
ENGR 111A Fall 2004

13. In-Class Exercise 13.1-2 (10-min)
Individually work T5.2-2 on p. 280
Pay attention to the section Hints for Improving Plots on p
9/20/2018
ENGR 111A Fall 2004

14. Solution x = [0 1 2 3 4 5]; y1 = [11 13 8 7 5 9]; y2 = [2 4 5 3 2 4];
plot(x, y1, 'ko-')
hold on
plot(x, y2, 'kd--')
legend('Data set 1', 'Data set 2')
xlabel('Independent variable [--]')
ylabel('Dependent variable [--]')
9/20/2018
ENGR 111A Fall 2004

15. Solution, continued
9/20/2018
ENGR 111A Fall 2004

16. 5.3 Special Plot Types (p. 282) loglog(x, y, ‘csl’)
semilogx(x, y, ‘csl’)
semilogy(x, y, ‘csl’)
plotyy(x1, y1, ‘csl’, x2, y2, ‘csl’)
9/20/2018
ENGR 111A Fall 2004

17. Matlab Handles
Handle: an index that relates to an object so that its properties can be changed.
h = plot(x,y)
set(h) will list all the things that can be set
get(h) will list all current settings
set(h,‘Property’, value) changes settings
9/20/2018
ENGR 111A Fall 2004

18. Automatic handles
Just like ans stores answers in a default variable, figure handles are stored automatically.
gca “get current axes” : handle to the current set of axes.
gcf “get current figure” : handle to the current figure.
9/20/2018
ENGR 111A Fall 2004

19. Labeling plotyy() axes
ax = plotyy(x1, y1, x2, y2)
axes(ax(1))
ylabel(‘y1 label’)
axes(ax(2))
ylabel(‘y2 label’)
9/20/2018
ENGR 111A Fall 2004

20. In-Class Exercise 13.1-3 (10-min)
Individually solve T5.3-1 on p. 291
You may learn how to use the Plot Editor (section 5.4) on your own to edit your plots.
9/20/2018
ENGR 111A Fall 2004

21. Solution x = 0:0.01:1.5; yp = 2*x.^(-0.5); ye = 10.^(1-x);
subplot(2,2,1)
plot(x, yp, 'k-', x, ye, 'k--')
axis([ ])
xlabel('x')
ylabel('y')
text(0.1, 2, 'Power')
text(0.3, 7, 'Exponential')
set(gca,'XTick',[0.5:0.5:1.5])
subplot(2,2,2)
semilogy(x, yp, 'k-', x, ye, 'k--')
axis([ ])
xlabel('x')
ylabel('y')
text(0.4, 0.6, 'Exponential')
text(0.8, 3, 'Power')
set(gca,'XTick',[0.5:0.5:1.5])
set(gca,'YTick',[1 10])
subplot(2,2,3)
loglog(x, yp, 'k-', x, ye, 'k--')
axis([ ])
text(0.05, 2.5, 'Power')
text(0.13, 10, 'Exponential')
set(gca,'XTick',[ ])
9/20/2018
ENGR 111A Fall 2004

22. Solution, continued
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ENGR 111A Fall 2004

23. 5.4 The Plot Editor (p. 292)
Sometimes it may be easier to work on plots using the plot function, etc.
The Plot Editor is a good way to move text around, alter plot scales, add tick marks, etc.
Rotating plots is VERY tricky.
Read through pages and practice the various features.
9/20/2018
ENGR 111A Fall 2004

24. 5.4 The Plot Editor (contd.)
Practice copying a figure (use one that you have just created) and paste it in a Word file.
Use the Copy Figure option in the Edit menu on the figure window.
9/20/2018
ENGR 111A Fall 2004

25. 5.8 3-D Plots (p. 334)
3-D plots are a lot like 2-D plots; just add the z-axis parameters.
There are three kinds of 3-D plots:
Three Dimensional Line Plots (p. 334).
Surface Mesh Plots (p. 335).
Contour Plots (p. 337).
3-D plot functions are in Table (p. 338).
9/20/2018
ENGR 111A Fall 2004

26. Surface plots For x = xmin : dx : xmax And y = ymin : dy : ymax
Use [x, y] = meshgrid(x, y) to generate a grid to calculate z on
Then use, for example: z = x.^2 + y.^2 mesh(x, y, z) % or surf(x, y, z)
9/20/2018
ENGR 111A Fall 2004

27. Contour plots
To label contours, use clabel: x = xmin : dx : xmax y = ymin : dy : ymax [x, y] = meshgrid(x, y) z = ??? [cs, h] = contour(x, y, z) clabel(cs, h)
9/20/2018
ENGR 111A Fall 2004

28. In-Class Exercise 13.1-4 (10-min)
Finally, work T5.8-1 on p Plot the data for x & y values from -5 to 5 in 0.5 increments and the z values from -20 to Be sure to label the contours on the contour plot.
9/20/2018
ENGR 111A Fall 2004

29. Solution [x, y] = meshgrid(-5:0.5:5) z = (x-2).^2 + 2*x.*y + y.^2;
subplot(2,2,1)
surf(x,y,z)
xlabel('x')
ylabel('y')
zlabel('z')
axis([ ])
subplot(2,2,2)
[cs,h] = contour(x,y,z)
clabel(cs,h)
9/20/2018
ENGR 111A Fall 2004

30. Solution, continued
9/20/2018
ENGR 111A Fall 2004

31. Assignment 13.1 Individual assignment.
Palm MatLab – Chapter 5 (starting on p. 344): # 19, 25, 50.
Due: In one week.
Reading Assignment – Sections 5.5 to 5.7.
9/20/2018
ENGR 111A Fall 2004