MATLAB Functions

Two-dimensional contour plot

contour(Z)
contour(Z,n)
contour(Z,v)
contour(X,Y,Z)
contour(X,Y,Z,n)
contour(X,Y,Z,v)
contour(...,LineSpec)
[C,h] = contour(...)

Description

A contour plot displays isolines of matrix Z. You label the contour lines using clabel.

contour(Z)

draws a contour plot of matrix Z, where Z is interpreted as heights with respect to the x-y plane. Z must be at least a 2-by-2 matrix. The number of contour levels and the values of the contour levels are chosen automatically based on the minimum and maximum values of Z. The ranges of the x- and y-axis are [1:n] and [1:m], where [m,n] = size(Z).

contour(Z,n)

draws a contour plot of matrix Z with n contour levels.

contour(Z,v)

draws a contour plot of matrix Z with contour lines at the data values specified in vector v. The number of contour levels is equal to length(v). To draw a single contour of level i, use contour(Z,[i i]).

contour(X,Y,Z), contour(X,Y,Z,n), and contour(X,Y,Z,v)

draw contour plots of Z. X and Y specify the x- and y-axis limits. When X and Y are matrices, they must be the same size as Z, in which case they specify a surface as surf does.

contour(...,LineSpec)

draws the contours using the line type and color specified by LineSpec. Marker symbols are ignored.

[C,h] = contour(...)

returns the contour matrix C (see contourc) and a vector of handles to graphics objects. clabel uses the contour matrix C to create the labels. contour creates Patch graphics objects unless you specify LineSpec, in which case contour creates Line graphics objects.

Remarks

If you do not specify LineSpec, colormap and caxis control the color.

If X or Y is irregularly spaced, contour calculates contours using a regularly spaced contour grid, then transforms the data to X or Y.

Examples

To view a contour plot of the function

over the range -2

2, -2

3, create matrix Z using the statements

xrange = -2:.2:2; 
yrange = -2:.2:3;
[X,Y] = meshgrid(xrange,yrange);
Z = X.*exp(-X.^2-Y.^2);

Then, generate a contour plot of Z:

[C,h] = contour(X,Y,Z);
clabel(C,h)

View the same function using the default range and 20 evenly spaced contour lines:

contour(Z,20);

Use interp2 and contour to create smoother contours:

Z = magic(4);
[C,h] = contour(interp2(Z,4));
clabel(C,h)