`contour`

Draws contour lines, the curves along which a function of two variables is constant.

Syntax

contour(Z)

Contour lines of the matrix Z, using column and row indices as coordinates.

contour(X, Y, Z)

Uses the coordinates X and Y.

contour(___, levels)

A scalar sets the number of levels; a vector sets the levels themselves.

[C, h] = contour(___)

Also returns the contour matrix and the contour object.

Description

A contour map shows a surface from above, like the lines of equal height on a topographic map. Closely spaced lines mean a steep slope. Use contourf to fill the regions between lines and contour3 to lift the lines to their height.

Input arguments

Z: Matrix of values.
X, Y: Coordinates of the grid: matrices the size of Z, or vectors matching its columns and rows.
levels: Number of levels or vector of level values. A vector with one value draws a single line.

Output arguments

C: Contour matrix, see contourc.
h: The Contour object; its LevelList property lists the levels drawn.

Example

Levels of a paraboloid

[X, Y] = meshgrid(-2:0.1:2);
Z = X.^2 + Y.^2;
[C, h] = contour(X, Y, Z, [1 2 3]);
disp(h.LevelList)
axis equal

Output

     1     2     3

contour