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contour - Contour plot of matrix

GUI Alternatives

To graph selected variables, use the Plot Selector in the Workspace Browser, or use the Figure Palette Plot Catalog. Manipulate graphs in plot edit mode with the Property Editor. For details, see "Plotting Tools — Interactive Plotting" in the MATLAB Graphics documentation and "Creating Graphics from the Workspace Browser" in the MATLAB Desktop Tools and Development Environment documentation.

Syntax

contour(Z) contour(Z,n) contour(Z,v) contour(X,Y,Z) contour(X,Y,Z,n) contour(X,Y,Z,v) contour(...,LineSpec) contour(axes_handle,...) [C,h] = contour(...) [C,h] = contour('v6',...)

Description

A contour plot displays isolines of matrix Z. 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 that contains at least two different values. The number of contour lines and the values of the contour lines 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 the monotonically increasing 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]). Specifying the vector v sets the LevelListMode to manual to allow user control over contour levels. See contourgroup properties for more information.

contour(X,Y,Z), contour(X,Y,Z,n), and contour(X,Y,Z,v) draw contour plots of Z using X and Y to determine the x- and y-axis limits. When X and Y are matrices, they must be the same size as Z and must be monotonically increasing.

contour(...,LineSpec) draws the contours using the line type and color specified by LineSpec. contour ignores marker symbols.

contour(axes_handle,...) plots into axes gerkaxes_handle instead of gca.

[C,h] = contour(...) returns a contour matrix, C, that contains the x, y coordinates and contour levels for contour lines derived by the low-level contourc function, and a handle, h, to a contourgroup object. The clabel function uses contour matrix C to label the contour lines. ContourMatrix is also a read-only Contourgroup property that you can obtain from the returned handle.

Backward Compatibility

[C,h] = contour('v6',...)returns the contour matrix C, as calculated by the function contourc and used by clabel, a vector of handles h to patch graphics objects instead of a contourgroup object, for compatibility with MATLAB Version 6.5 and earlier. When called with the 'v6' flag, contour creates patch graphics objects, unless you specify a LineSpec, in which case contour creates line graphics objects. In this case, contour lines are not mapped to colors in the figure colormap, but are colored using the colors defined in the axes ColorOrder property. If you do not specify a LineSpec argument, the figure colormap and the color limits (caxis) control the color of the contour lines (patch objects).

Note The v6 option enables users of MATLAB Version 7.x to create FIG-files that previous versions can open. It is obsolete and will be removed in a future version of MATLAB.

See Plot Objects and Backward Compatibility for more information.

Remarks

Use contourgroup object properties to control the contour plot appearance.

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

Examples

Contour Plot of a Function

Create a contour plot of the peaks function using the contour matrix and contourgroup object handle as output.

[C,h] = contour(peaks(20),10);
colormap autumn

Smoothing Contour Data

Use interp2 to create smoother contours. Also set the contour label text BackgroundColor to a light yellow and the EdgeColor to light gray.

Z = peaks;
[C,h] = contour(interp2(Z,4));
text_handle = clabel(C,h);
set(text_handle,'BackgroundColor',[1 1 .6],...
    'Edgecolor',[.7 .7 .7])

For more examples using contour, see Contour Plots.