Page 88 - A Guide to MATLAB for Beginners and Experienced Users

Two-Dimensional Plots 69

Contour Plots and Implicit Plots
A contour plot of a function of two variables is a plot of the level curves of the
function, that is, sets of points in the x-y plane where the function assumes
2
2
a constant value. For example, the level curves of x + y are circles centered
at the origin, and the levels are the squares of the radii of the circles. Contour
plots are produced in MATLAB with meshgrid and contour. The command
meshgrid produces a grid of points in a specified rectangular region, witha
specified spacing. This grid is used by contour to produce a contour plot in
the specified region.
2
2
We can make a contour plot of x + y as follows:
>> [X Y] = meshgrid(-3:0.1:3, -3:0.1:3);
>> contour(X, Y, X.ˆ2 + Y.ˆ2)
>> axis square

The plot is shown in Figure 5-2. We have used MATLAB’s vector notation to

3

2

1

0

-1

-2

-3
-3 -2 -1 0 1 2 3
Figure 5-2