2.1.1 Simple 2D plots

Functions of a single variable, e.g., y(x), are normally plotted in a conventional 2-D plot. Do the following to make a plot of the sine curve between zero and $2\pi$. (Remember, at this stage, you should really enter the commands into an M-file and then execute (shortcut: hit F5) the M-file rather than entering all the commands directly at the command line. You don't need to enter any of the comments, which are marked by %.)

% Our first plot
x = linspace(0,2*pi,100); % get 100 evenly spaced values between 0 and 2 pi
y = sin(x); % Compute the sine at these points and store in variable y
plot(x,y) % plot the results

The linspace command creates 100 evenly spaced points starting at zero and ending at $2\pi$. This is similar to the thing you tried in Sec. 1.4.1 (e.g., x=[0:2*pi/100:2*pi]) except that instead of choosing the step size explicitly, linspace allows you to choose the number of points instead and makes MATLAB figure out the step size. The second statement takes the array of 100 points and calculates the sine at each point and stores the results in the $\verb=y=$ array. The plot command then plots y vs. x. (See Figure 2.1.) The plot is displayed in a separate window called Figure No. 1.

Figure 2.1: Simple plot of a sine curve.

You could have also used the plot command this way plot(x,sin(x)) without explicitly storing the function values in y. Try it. By default, MATLAB plots the data by connecting the individual data points. The plot command can be changed so that only the points are drawn instead of lines. Try plot(x,y,'o') (the letter ``oh'' between single quotes). Now try plot(x,y,'-*'). This tells MATLAB to connect the points with a dotted line and mark each point with a star. Try it. You can also change the color--try plot(x,y,'r-*'). A list of all the style options that can be used with plot are summarized in Table 2.1. You can also see them by typing help plot. Experiment with three or four different plot styles of your own design.

Table 2.1: Style options for the plot command.

Color-style options		Marker-style options		Line-style options
b	blue	.	point	-	solid
g	green	o	circle	:	dotted
r	red	x	cross	-.	dashdot
c	cyan	+	plus	-	dashed
m	magenta	*	asterisk
y	yellow	s	square
k	black	d	diamond
		v	triangle (down)
		^	triangle (up)
		<	triangle (left)
		>	triangle (right)
		p	5-pointed star
		h	6-pointed star

We can also add labels to the axes, control the plotting range, change the aspect ratio of the plot, etc. For example, try the following:

% Making our first plot fancier
x = linspace(0,2*pi,100); % get 100 evenly spaced values between 0 and 2 pi
y = sin(x); % Compute the sine at these points and store in variable y
plot(x,y,'r-',x,y,'x') % plot the results with a red line and blue crosses
axis square % Make the plot square
xlabel('angle \theta') % Label the x axis
ylabel('sin(\theta)') % Label the y axis
title('Pretty plot of a sine curve') % Add a title label to the plot
axis([0 2*pi -1.1 1.1]) % Set the x and y ranges of the plot

Figure 2.2: Fancier plot of a sine curve.

If it's unclear what any of the commands do, try looking them using the help command.