1. Plotting Signals in MATLAB
Lecture 4:
Plotting Signals in MATLAB
1st semester
By: Elham Sunbu

2. Outline Graph in MatLab 2-D plotting 1. Creating and Type of graph
2. Using Basic Plotting Functions
3. Plotting Multiple graph in same plot
4. Formatting plots

3. Creating Graph in MATLAB
Line Plot
Pie Charts, Bar Plots, and Histograms
Command
Description
bar, bar3
Bar graph 2-D, 3-D
Pie, pie3
Pie graph 2-D, 3-D
hist
Histogram plot
Command
Description
Plot, plot3
Create 2-D graph and 3-D
plotyy
2-D line plots with y-axes on both left and right side
Discrete Graph
Command
Description
Stem, stem3
Plot discrete sequence data 2-D, 3-D
stairs
Stairstep graph

4. 2-D Plotting - Specify x-data and/or y-data - Syntax:
- Specify color, line style and marker symbol
(Default values used if ‘clm not specified)
- Syntax:
Plotting single line:
plot(xdata, ydata, 'color_linestyle_marker')
Plotting multiple lines:
If data is given, the information is entered as the elements of the vectors x and y.
If the values of y are determined by a function from the values of x, than a vector x is created first, and then the values of y are calculated for each value of x.
The PLOT functions is used to produce 2-dimensional curves, using x- and y-data matrices specified by the user. However, PLOT also accepts character-string arguments that designate various colors, line styles and marker symbols for the resulting line.
For example, to produce a red dotted line with square markers at each data point, type:
» plot(x, y, 'r:square')
You can plot multiple lines at once, using pairs of x- and y-data. As with plotting single lines, the color, line style and marker information can be specified explicitly. However, if not specified, MATLAB automatically cycles through a predefined (but user settable) list of colors to identify each line. For example, the following statement plots three lines as a function of t (First = blue / Second = green / Third = red):
» plot(t, y1, t, y2, t, y3)
plot(x1, y1, 'clm1', x2, y2, 'clm2', ...)

5. Line Specification
Three components can be specified in the string specifiers along with the plotting command. They are:
Line style
Marker symbol
Color
iers
Meaning
'-'
Solid line (default)
'--'
Dashed line
':'
Dotted line
'-.'
Dash-dot line

6. Line Specification Meaning Color Specifiers Blue b Cyan c Green g
Black k
Magenta m
Red r
Yellow y
Meaning
Marker
down v
circle o
triangle left
<
diamond d
triangle right
>
hexagram h
up triangle ^
pentagram p
x -mark x
plus +
point .
square s
star *

7. 2-D Plotting - Example » x = 0:.1:2*pi; » y = sin(x); » plot(x,y)
- Create a Blue Sine Wave
» x = 0:.1:2*pi;
» y = sin(x);
» plot(x,y)
In this example, the data plotted along the x-axis is defined as:
» x=0:0.1:2*pi;
The data plotted along the y-axis is defined as:
» y=sin(x);
Plot these data as follows (default = blue, solid line, no marker):
» plot(x,y)

8. Adding a Grid
- GRID ON creates a grid on the current figure
- GRID OFF turns off the grid from the current figure
- GRID toggles the grid state
grid on

9. Controlling the Axes
- Setting Axis Limits & Grids
The axis command lets you to specify your own limits:
axis([xmin xmax ymin ymax])
You can use the axis command to make the axes visible or invisible:
axis on / axis off
The grid command toggles grid lines on and off: grid on / grid off

10. Using Basic Plotting Functions
- The following commands are useful when plotting:
Note that all text must be put within ' '.
Graphing functions
MATLAB command
Label the horizontal axis.
xlabel('text')
Label the vertical axis.
ylabel('text')
Attach a title to the plot.
title('text')
Change the limits on the x and y axis.
axis([xmin xmax ymin ymax])
"Keep plotting in the same window."
hold on
Turn off the "keep-plotting-in-the-same-window-command".
hold off
using the strings to label various curves
legend(‘string1’,’string2’,’string3’)
Places the string (text) on the plot at coordinate x,y relative to the plot axes.
text(x,y,’string’)
The title (), xlabel (), and ylabel () commands take a string argument in single quotes in order to label the top of the plot, the x-axis, and the y-axis, respectively. The axis () command takes a 2 or 4 element vector as its argument where the minimum and maximum x values are set or the minimum and maximum x and y values are set. Matlab will probably complain loudly if either xmax or ymax is less than xmin or ymin. The use of the axis () command allows the user to override the default setting that Matlab would otherwise pick. It can be use to look closely at a small window of data which would otherwise be unclear if a lot of points where available. It can be particularly useful when making an interactive plot that needs to resize itself.
The legend () command allows us to place a legend on a plot. The legend () command takes as its arguments a list of strings enclosed in single quotes that are the explanatory information you would like displayed next to a short sample of the line and data point display for a given set of data. The order of the strings must correspond to the order of the graphs that were added to the plot. In addition to the string, the legend () command can take a position argument that dictates where the legend is to be placed on the plot. The default is the upper right corner of the plot.
The text () command takes three arguments: an x and y location to begin writing a string and the text string that you would like displayed. The string must be enclosed in single quotes. The x and y location must be supplied in the same scale that is being used for the x and y axes. In other words, the location of the text string is relative to the plot. Fixed screen locations do not exist.

11. Adding Additional Plots to a Figure
PLOTTING MULTIPLE GRAPHS IN THE SAME PLOT
Plotting two (or more) graphs in one plot:
Using the plot command.
2. Using the hold on, hold off commands.
In addition to supplying multiple vector pairs to the plot () command, we can create graphs with multiple plots by using the hold on/hold off commands. Once a plot () command has been issued and hold on specified, all subsequent plot () commands will be plotted on the initial graph. Axis properties will be maintained for subsequent plots. If line specifiers are not specified in the subsequent plots, Matlab will use the default order and colors when drawing additional plots on the graph. To return to the default situation in which each plot () command causes a new plot to be drawn in the graph window, the hold off command must be issued.

12. Subplots

13. Formatting Plots
- A plot can be formatted to have a required appearance.
- With formatting you can:
Add title to the plot.
Add labels to axes.
Change range of the axes.
Add legend.
Add text blocks.
Add grid.

14. Thank You