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MATLAB Plotting

Plotting is a graphical representation of a data set that shows a relationship between two or more variables. MATLAB plots play an essential role in the field of mathematics, science, engineering, technology, and finance for statistics and data analysis.

There are several functions available in MATLAB to create 2-dimensional and 3-dimensional plots.

Creating Plotting

MATLAB makes it easy to create plots. For example in 2D, is to take a vector of a– coordinates, a = (a₁… a_n ), and a vector of b-coordinates, b = (b₁…b_n), locate the points (a_i…b_i), with i = 1, 2. . . n and then connect them by straight lines.

The MATLAB commands to plot a graph is plot (a, b).

The vectors a = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10) and b = (0, 1, -1, 1, 0) produce the picture shown in figure.

Example: Plot the function sin (a) on the interval [0, 3π], we first create a vector of a values ranging from 0 to 3π, then compute the sine of these values, and finally plot the result:

Note: 0:pi/100:3*pi yields a vector that

• It starts at 0,
• takes steps (or increments) of π/100,
• stops when 3π is reached.
• If you ignore the increment, MATLAB automatically increments by 1.

Adding titles, axis labels, and annotations

MATLAB allows us to add axis labels and titles. For example, using the graphs from the previous example, add and a and b labels. Now labels the axes and add a title. The character pi generates the symbol π. An example of a 2D plot is shown in the figure.

The color of a single curve are, by default, blue, but other colors are possible. The desired color is denoted by a third argument. For example, red is picked by plot (x, y,’r’). Note that the single quotes, ‘ ‘, around r.

Creating Multiple Plots

A plot with more than one line can be created in several methods. The following example demonstrates the concept:

Example:

The output of multiple data sets in one graph plot is shown in the figure

Line, Color, and Mark Style

The style option in the plot command are a character string that consists of one, two, or three characters that specify the color and line style. There are several color, line, and marker-style options:

Color Style-option	Line Style option	Marker Style-option
y yellow	–     Solid	+     plus sign
m magenta	—     dashed	0     circle
c cyan	:     dotted	*     asterisk
r red	-.     dash-dot	x     x-mark
g green	none     no line	.     point
b blue		^     up triangle
w white		s     square
k black		d     diamond, etc.

The following commands demonstrate the use of line, color, and mark styles:

The resulting plot fig (a) consists of a dashed line, together with data points marked with circles. The line, the points, and the circles are drawn in black, as shown in fig (b).

Setting Axis Scales and Annotation Plots

The axis command allows us to set the axis scales. We can provide minimum and maximum values for x and y axes using the axis command in the following method

Example

There are also some predefined string arguments for the axis command:

axis (‘equal’)	Sets equal scale on both axes
axis (‘square’)	Sets the default rectangular frame to the square
axis (‘normal’)	Resets the axis to default values
axis (‘axis’)	Freezes the current axis limits
axis (‘off’)	Delete the surrounding frame and the tick marks.

Generating Sub-Plots

We can use the subplot function to display multiple plots in different sub-regions of the same window. The subplot commands require three integer arguments:

Splits the figure into an m x n matrix. The variable p identifies the part of the window where the next plot will be drawn. For example, if the command

is used, the window is split into two rows and two columns, and the plot is drawn in the upper left-hand window.

Fig: Subplots are used to subdivide the figure window into an m x n matrix.

Example:

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