June 2

1
June 2

• GRAPHICS IN MATLAB- PART I
• BASIC PLOTTING

2
PLOTTING A SINGLE ARRAY

• The most basic command that puts a graphic on
  screen is plot
• If y is an array, plot(y) simply plots values of
  y vs. their array index position
• Do this
• t00.011
• ycos(2pit)
• plot(y)
• Notice numbers on x-axis. They are not time

3
PLOTTING ONE ARRAY AGAINST ANOTHER

• If t is one array and y another, plot(t,y) plots
  y vs. t.
• Do this
• t00.011
• ycos(t)
• plot(t,y)

4
Try it!

• Plotting one array against another generates
  creative figures
• For example, define your x-array as cos(2(pi)t)
  and y-array as sin(2(pi)t). Then plot y vs.x. Let
  t run from 0 to 1 as before
• Do the same for 2cos(2(pi)t) vs. 4sin(2(pi)t)

5
Plots via a matrix

• The argument of plot can be a matrix. In this
  case, each column is plotted separately on the
  same axis. This is a compact way of plotting
  several graphs on the same axis
• Try
• t0pi/16/2pi
• xcos(t),sin(t)
• plot(x)

each column is plotted separately vs. position
6
Plotting a matrix against another array

• Let Y be a matrix and x be the vector of
  variables , then
• plot(x,Y) plots columns of Y vs. x on the same
  graph
• Try this
• t0pi/162pi
• Ycos(t),sin(t)
• plot(t,Y)

each column plotted separately vs. another array
7
Putting multiple plots on the same graph

• There are 3 ways to do this. Want to plot 3 data
  vectors y1,y2 and y3 vs. t
• Method 1
• Yy1,y2,y3
• plot(t,Y)
• Method 2
• plot(t,y1,t,y2,t,y3)
• Method 3
• Use hold command

8
RC circuit response

• Capacitors charge and discharge following an
  exponential curve. Plot the following 3 voltages
  on the same graph for 0

9
Try it!
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hold COMMAND

• Once hold is turned on, all subsequent plot
  commands are superimposed on the same axis
• hold cycles between on and off.
• For example,
• plot(t,y1)
• hold on
• plot(t,y2)
• plot(t,y3)
• hold off

11
Homework 1

• Plot y vs. x over the range x-2,2. In addition
  to your m-file, save your figure and send it to me

12
Plotting parametric functions- fplot.

• You may want to plot a function, rather than an
  array of numebrs, against a variable.
• Example is plotting cos(x). The command is
• fplot(cos,-pi pi)
• Note that the function must be known to MATLAB
  such as sine and cosine

x range
function
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MULTIPLE PLOTS USING fplot

• fplot(sinc(x),sinc(2x),-2 2)

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CONTROLLING LINE TYPES

• We can select line styles and colors in a graph
• Simply pass a character string to plot
• plot(t,x,s)
• For example, sr, puts red plus() marks for
  every data point.
• MATLAB accepts many other choices.
• Redo the exponentials using different styles

15
Homework 2

• Plot the 3 exponentials on slide 8
  simultaneously.
• 1. Use red, green and blue solid lines
  respectively
• 2. Use red plus sign(), green star() and blue
  dots (.) for each graph

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SPECIALIZED 2D PLOTTING FUNCTIONS

• For each item write an m-code to see the plots.
  Read the example slides
• bar - creates a, well, bar graph
• polar - creates a (??????plot
• hist - creates a histogram of data
• fill - fills the curve with solid colors
• stairs - similar to bar but without internal lines

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bar

• Usage
• bar(x,y)
• plot the shape of a normal distribution given by
  yexp(-x2) in the range (-2,2).

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fill

• Usage
• fill(x,y,b) where b indicates a blue fill.
• plot the function exp(-t2), in the range (-2,2)

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polar

• Usage
• polar(theta,rho)
• Plot

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stairs

• Usage
• stairs(x,y)
• plot the function exp(-x2), in the range (-4,4)

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ADDING LABELS AND TITLES

• There are numerous ways the appearance of a plot
  can be controlled. The most obvious ones are
  through
• axis labels
• figure title
• legend
• grid

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LABEL USAGE

• axis labels
• xlabel(time)
• ylabel(voltage)
• Figure title
• title(Capacitor voltage)
• Legend
• legend(first,second,third)
• Grid
• grid - places a grid over the plot

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Try it!
24
Homework 3

• Over a time range -3, 3, plot the following 3
  functions simultaneously using the matrix method
  of slide 7
• ye-4xcos(2pix)