1. Lecture 25: Exploring data

2. Two Dimensional Plots
The xy plot is the most commonly used plot by engineers
The independent variable is usually called x
The dependent variable is usually called y

3. Define x and y and call the plot function

4. Engineers always add … Title X axis label, complete with units
title(‘y = cos(x)’)
X axis label, complete with units
xlabel(‘x-axis’)
Y axis label, complete with units
ylabel(‘y-axix’)
Often it is useful to add a grid
grid on
Single quotes are used.

5. Creating multiple plots
MATLAB overwrites the figure window every time you request a new plot
To open a new figure window use the figure function – for example figure(2)

6. Create multiple lines on a single graph
Each set of ordered pairs will produce a new line

7. Use alternating sets of ordered pairs
If you want to create multiple plots, all with the same x value you can…
Use alternating sets of ordered pairs
plot(x,y1,x,y2,x,y3,x,y4)
Or group the y values into a matrix
z=[y1;y2;y3;y4]
plot(x,z)
x = 0:pi/100:2*pi;
y1 = cos(x);
y2 = cos(x)*2;
y3 = cos(x)*4;
y4 = cos(x)*6;

8. Line, Color and Mark Style
You can change the appearance of your plots by selecting user defined
line styles
mark styles
color
Try using help plot for a list of available styles

9. Specify your choices in a string
For example
plot(x, y, ':ok')
strings are identified with single quotes
the : means use a dotted line
the o means use a circle to mark each point
the letter k indicates that the graph should be drawn in black
(b indicates blue)

10. Available choices Table 5. 2 Line, Mark and Color Options Line Type
Indicator
Point Type
Color
solid -
point .
blue b
dotted :
circle o
green g
dash-dot -.
x-mark x
red r
dashed --
plus +
cyan c
star *
magenta m
square s
yellow y
diamond d
black k
triangle down v
triangle up ^
triangle left
<
triangle right
>
pentagram p
hexagram h

11. specify the drawing parameters for each line after the ordered pairs that define the line

12. Axis scaling
MATLAB automatically scales each plot to completely fill the graph
If you want to specify a different axis – use the axis command
axis([xmin,xmax,ymin,ymax])
axis([0, 11, 0, 200])

13. Annotating Your Plots You can also add Of course you should always add
Legends
legend(‘string1’, ‘string2’, etc)
The legend shows a sample of the line, and
Lists the string specified.
Textbox
text(x_coordinate, y_coordinate, ‘string’)
The box is placed at the specified x and y coordinates, and
Contains the string value specified.
Of course you should always add
title
axis labels

14. 4

15. Subplots
The subplot command allows you to subdivide the graphing window into a grid of m rows and n columns
subplot(m,n,p)
rows
columns
location

16. subplot(2,2,1)
2 columns 2 1
2 rows 3 4

17. 2 rows and 1 column

18. Saving your plots Rerun your M-file to recreate a plot
Save the figure from the file menu using the save as… option
You’ll be presented with several choices of file format such as
jpeg
emg (enhanced metafile) etc

19. Other Types of 2-D Plots Polar Plots Logarithmic Plots Bar Graphs
Pie Charts
Histograms
X-Y graphs with 2 y axes
Function Plots

20. Three Dimensional Plotting
Line plots
Surface plots
Contour plots
x = [-2:0.1:2];
y = [-2:0.1:2];
[X, Y] = meshgrid(x, y);
Z = X.*exp(-X.^2 - Y.^2);
surf(X, Y, Z)

21. Practice Question Q. How many times will “Winter is over!!” print out?
int main( void ) {
int x = 3;
int y = 1;
do {
printf(“Winter is over!!\n”);
if (x > y) {
x = 0;
y = 2; }
x++;
} while (x < y);
It may never stop printing. 1 2 3
Solution: D