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EGR 106 Lecture 62-D Plotting
Graphical presentation has become the standard method to show technical information. Engineers use plots to analyze, visualize, and present their work.
Matlab has many useful plotting options available!
We’ll review some of them today.
Textbook 5.1, 5.3-5.12
What Would You Rather See?
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or
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Example Problem:
x = –3:0.1:3;
y = x.^3 – 5*x.^2 + 4;
plot(x,y)
xlabel('value of x')
ylabel('value of y')
title('Problem 10')
text(0,1, 'egr106 week 1')
colon and dotnotation forarrays standard form
for plot
annotation tools
scales areautomatic
default isFigure 1,blue lines,and smalltext
note axis labels & text
Matlab has interactive tools for modifying plots within the Figure window
Click on the arrow to start interaction
Double click on some part of the figure to initiate choices
Modify text:
Or the lines themselves:
So, the property editor is like a spreadsheet’s tools, but…..– is limited to a single figure– is tedious to repeat for other plots
Command line manipulation is available through optional additional arguments:
plot(x,y, 'linespec' , 'Propname' , PropValue )
– line specifiers: color, line type, markers for data– property name and value: thickness, size, etc
Line Specifiers
plot(x,y, ' r : d ' )
red
dotted line
diamonds
General form: plot(x,y, '  ')
Color:k black
r red
b blue
g green
y yellow
c cyan
w white
m magenta
Line type:- solid
: dotted
-- dashed
-. dash-dotSymbol:
. point
o circle
x x-mark
s square
d diamond
etc.
The order is not important !
Line Properties and Values
plot(x,y, 'linewidth',5 )
line width is 5 “points”
General form: plot(x,y,’  ’,value)
Properties:linewidth
markersize
markeredgecolor
markerfacecolor
Value: varies with each property
sizes in points
colors as strings
Can have multiple pairs !
Example:
plot(x,y, '- k o' , 'LineWidth' , 3 , 'MarkerSize', 6,…
'MarkerEdgeColor','red','MarkerFaceColor','green')
Multiple Plots on the Same Axes
Plot allows multiple sets of arrays and line specifiers:
Note colors rotate
Can also use hold to freeze the plot
Now, note colors
Two Useful Commands
figure– alone it opens a new window – figure(n) takes you to window n
ginput(1) – creates crosshairs on the screen– returns (x,y) location of cursor at mouse click– ginput(n) returns n pairs of locations
Formatting Plots – Adding Text
– xlabel( 'string' )– ylabel( 'string' )– title( 'string' )– text( x, y, 'string' )– gtext( 'string' ) – cursor controlled – legend( 'string1', … 'stringn', loc)
Location where text is started
Can add greek letters, sub and superscripts E.g. gtext( '\beta_1 x^2' )
Text properties allow manipulation of the look for example:
gtext( 'cosine' , 'fontsize', 20, 'rotation', 45, 'color' , 'red', )
Formatting Plots – The Axes
Adding a grid
gridSetting the axis limits:
axis( [ xmin xmax ymin ymax ] )
Example
Can plot on logarithmic axes using:
semilogx(x,y)
semilogy(x,y)
loglog(x,y)
Note – negative data is ignored
Figure Files (not in the text)
Save to create a .fig file
Figures outside Matlab (not in the text)
Print them: Copy for pasting
Multiple Axes in One Figure - Subplot
subplot(2,2,1)
plot(x1,y1)
subplot(2,2,2)
etc.
Argument list is:rows, columns,
choice
Other Types of 2-D Plots - Polar
x = 1:100;
r = log10(x);
t = x/10;
polar( t, r )
magnitude
angle in radians
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Vertical and horizontal bar plots, stem and stair plots, pie and compass plots:
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Histograms:
Additional Notes
Line specifiers, properties, axis, grid, … work on many of the plot types
Most of these tools have additional features – use the help function
Three-dimensional plots are available (see chapter 10) with various viewpoint options. Will do these later in semester.
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Three-Dim. Examples
For array arguments:plot(x_array, y_array)
– plots column by column– cycles through colors
For a single argument, plot(x):– plots imaginary versus real if x is complex– plots x versus index if x is real
Other Special Cases:
MATALB Allows High Level Interfaces –
Graphical User Interfaces (GUI)