Chapter 4 Review

1
Chapter 4 Review

• Introduction to MATLAB 7
• Engineering 161

2
Plotting

• Large tables and reams of data are difficult to
  interpret.
• Graphing techniques facilitate seeing trends,
  picking out highs and lows, and serve as a quick
  check on ones calculations.
• Most common plot is the x-y plot, i.e., a two
  dimensional plot.
• MATLAB is rich in both 2 and 3 dimensional
  graphing capabilities. We are going to study 2
  dimensional plotting.

3
Plotting II

• When we complete the material in Chapter 4, we
  will be able to
• Create and label 2-dimensional plots.
• Adjust the appearance of your plots.
• Use our plots to interpret our results.
• Have a basis for studying more complex MATLAB
  graphical capabilities.

4
Basic Plotting Concepts

• In general, through calculations or experimental
  measurements, we have amassed data where y
  f(x).
• We call x the independent variable and y the
  dependent variable. x and y are usually n
  dimensional vectors.
• Plotting is nothing more than a visual
  representation of the relationship between x and
  y.

5
Basic Plotting Concepts II

• The basic MATLAB plotting command is plot (x
  , y)
• The graph is generated in the MATLAB Graphics
  window and labeled as Figure 1 or 2, etc.
• Simple MATLAB commands allow you to label the x
  and y axes, label your graph, label legends, and
  format the graph as you want.

6
Basic Plotting Concepts III

• It is easy to plot multiple sets of data in a
  single graph,
• And to generate multiple graphs in a single
  Graphics Window. MATLAB calls these sub-plots.

7
Plotting Functions

• MATLAB supports a number of basic plotting
  functions in addition to the line chart. These
  include
• Bar Charts (vertical and horizontal, 3
  dimensional)
• Pie Charts (2 and 3 dimensional)
• Histograms
• Semilog plots
• Loglog plots
• Polar plots

8
Plotting Commands

• The basic plotting command is plot (x , y) where
  x is the independent variable and y is the
  dependent variable.
• plot (x, y1, x, y2) will plot two lines in the
  graph
• For y y1y2, plot (x , Y) will generate the
  same plot as above. When the dependent variable
  is a matrix, MATLAB plots each row of Y vs x.
• Another way to plot 2 lines on one graph is to
  use the hold on command
• plot (x,y1)
• hold on
• plot (x,y2)
• hold off
• Normally when MATLAB executes a plot command it
  erases the current figure and then plots anew.
  The command hold on suppresses the erase.

9
Plotting Commands II

• Labeling your graphs axes, and titling your chart
  is easy.
• Use the xlabel ( . . . .) and the ylabel (
  . . . .) commands to label your axes
  appropriately. You must surround your labels in
  single quotes. Single quotes tell MATLAB that it
  is a character string.
• Use the title ( . . . .) command to title the
  graph.
• Use the legend (line1, line2, line3)
  command to identify a designator with each line
  on your graph. The order of the entries
  corresponds to the order that you plotted the
  lines.
• Or use the Insert Tab on the Graphics Window
  toolbar to customize your graph. NOTE when you
  customize a graph interactively, i.e., using the
  Insert Tab, the next time you run the program,
  the customization is lost.

10
Plotting Commands III

• To open multiple figures use the Figure (n)
  command, Figure 1 is the default window, but
  after using this window to plot in, enter the
  command Figure (2) to create a new graphics
  window. The next time you plot, the 2nd graphics
  window will be used thereby preserving the
  results graphed in Figure 1. Both windows can be
  viewed as wanted.
• Dont forget when in need of information about
  the plot command, enter help plot in the
  Command Window for information.
• Finally, the command plot (y) makes sense to
  MATLAB. Here MATLAB uses the indices of the
  vector y as the x values.

11
Line, Color and Mark Style

• You can select line type, point type, and color
  for each of your plotted lines.
• See page 107 of the text for a Table of the
  option codes to use.
• For example, plot (x,y, og) will generate a
  dotted line, with a circle point type, and color
  green.
• Enter 1, 2 or 3 option codes in any order
  surrounded by single quotes to define the style
  you want to use with your line graph. The option
  codes need to immediately follow the x,y pair
  where they specify the style.
• When multiple lines are being plotted using a
  single plot command, follow each x,y pair with
  its option code in single quotes and separated by
  commas.
• When no option codes are present, MATLAB uses its
  default code, solid black line with no point type.

12
Axes Scaling

• Unless you choose to scale your axes, MATLAB will
  scale them automatically based upon the values in
  x and y. This is the easiest method.
• But, you can scale your axes with the axis (v)
  command where v xmin, xmax, ymin, ymax, that
  is, v is a 4 element row vector provided by you
  with the min and max values for each axes.
• The command axis without the argument v freezes
  the current axes scale for subsequent plots.
  Enter axis again to unfreeze.

13
Axes Scaling II

• Sometimes you will want to have two different
  vertical axes scaling, one on the left hand side
  of the graph and the other on the right hand
  side. To do this
• Use the plotyy (x, y1, x, y2) command to force
  MATLAB to scale the vertical axes independently
  for the two lines in your chart.
• Then use the Insert Tab in the graphics window to
  label the right hand vertical axis.
• The chart title, and x and left hand y axes
  labels can be added using the title, xlabel and
  ylabel commands. Only the right hand label needs
  to be added using the Insert Tab.

14
Subplots

• The subplot command allows you to split the
  graphics window into a number of sub-windows.
• You can choose two sub-windows arranged
  horizontally or vertically, or
• You can choose an array of sub-windows, say two
  rows with two columns or 4 subplots displayed at
  one time.
• More than 4 isnt too practical. Things get too
  small.

15
Subplots II

• The subplot command is specified in the following
  manner,
• subplot (m,n,p) where m, n, and p are integers
  m and n specify the size of the array of subplots
  and p specifies which subplot is being
  referenced. Subplots are numbered from left to
  right, top to bottom.
• subplot (2,2,3) would specify a 2 by 2 array of
  subplots with the 3 indicating the lower left
  hand plot in the array.
• To use this feature, you will do the following
• gtgt subplot (2,1,1) The subplot command
  proceeds
• gtgt plot (x,y) the plot command.
• Here two subplots are specified, one over the
  other, the plot takes place in the upper chart.

16
Subplots III

• Chart titling, axes labeling, etc., following the
  plot command will refer to the last subplot
  indicated. Any additional plot commands will
  also refer to the last subplot indicated. To
  select a new sub-window to plot in, you have to
  select that sub-window with a subplot command
  before you use the plot (x,y) command. You can
  graph multiple x,y pairs in each subplot, select
  the style, add legends, etc., just as you have
  learned how to do with a single graph.

17
Plotting from the Workspace Window

• MATLAB 7 allows you to create plots from the
  Workspace window. This lets you view
  intermediate results or any variable in the
  Workspace window.
• In the Workspace window, select the variable you
  want to plot. If more than one, hold down the
  Ctrl key and select the additional ones that you
  want plotted.
• Next click on the plotting icon, the squiggly
  line in the the Workspace toolbar. MATLAB
  selects what it thinks would be good plotting
  options based upon the data.
• Select your graph type and the graph is
  generated.
• Use More plots to see a complete list of plot
  options.

18
Chapter 4 Assignments

• Chapter 4 assignments let you practice plotting.
  They are,
• 4.1, 4.2, 4.5, 4.7, 4.9a and 4.9b