MATLAB Programming/Graphics

2D Graphics

Plot

The plot command renders a 2D line in Cartesian coordinates.

Example:

x=0:0.1:2;  % Creates a vector from 0 to 2, spaced by 0.1.
fx=(x+2)./x.^2; % calculates fx based on the values stored in x
plot(x,fx) % Plots 2D graphics of the function fx

Matlab also lets the user specify the line style. The following example generates the same graph as in the previous example, but plots the function with a specific line style: a black line with circle markers on each node:

x=linspace(0, 2, 21);  % like the previous example, creates a vector from 0 to 2, spaced by 0.1
fx= arrayfun(@(x) (x+2)/x^2, x); % like the previous example, calculates fx based on the values stored in x
plot(x,fx,'-ok') % Plots the graph of (x, fx) as a black line with circle markers at each point

To plot two or more graphs in one figure, simply append the second (x,y) pair to the first: The following example will plot y1 and y2 on the same x-axis in the output.

x1 = [1,2,3,4]
y1 = [1,2,3,4]
y2 = [4,3,2,1]
plot(x1,y1,x1,y2)

Polar Plot

Plots a function using θ and r(θ)

t = 0:.01:2*pi;
polar(t,sin(2*t).^2)

3D Graphics

plot3

The "plot3" command is very helpful and makes it easy to see three-dimensional images. It follows the same syntax as the "plot" command. If you search the MATLAB help (not at the command prompt. Go to the HELP tab at the top of the main bar and then type plot3 in the search), you will find all the instruction you need.

Example:

l=[-98.0556  ; 1187.074];       
f=[ -33.5448 ; -240.402];       
d=[ 1298     ; 1305.5]           
plot3(l,f,d); grid on;

This example plots a line in 3D. I created this code in an M-file. If you do the same, change the values and hit the run button in the menu bar to see the effect.

Mesh

Creates a 3D plot using vectors x and y, and a matrix z. If x is n elements long, and y is m elements long, z must be an m by n matrix.

Example:

x=[0:pi/90:2*pi]';
y=x';
z=sin(x*y);
mesh(x,y,z);

Contour

Creates a 2D plot of a 3D projection, using vectors x and y, and a matrix z. If x is n elements long, and y is m elements long, z must be an m by n matrix.

Example:

x=[0:pi/90:2*pi]';
y=x';
z=sin(x*y);
contour(x,y,z);

Contourf

Same as contour, but fills color between contour lines

Surface

Basically the same as mesh