CONTOUR Contour Plot Function

Section: Handle-Based Graphics

Usage

This command generates contour plots. There are several syntaxes for the command. The simplest is 
  contour(Z)

which generates a contour plot of the data in matrix Z, and will automatically select the contour levels. The x,y coordinates of the contour default to 1:n and 1:m, where n is the number of columns and m is the number of rows in the Z matrix. Alternately, you can specify a scalar n 

  contour(Z,n)

which indicates that you want n contour levels. For more control, you can provide a vector v containing the levels to contour. If you want to generate a contour for a particular level, you must pass a vector [t,t] where t is the level you want to contour. If you have data that lies on a particular X,Y grid, you can pass either vectors x,y or matrices X,Y to the contour function via 

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

Each form of contour can optionally take a line spec to indicate the color and linestyle of the contours to draw: 

  contour(...,linespec)

or any of the other forms of contour. Furthermore, you can supply an axis to target the contour plot to (so that it does not get added to the current axis, which is the default): 

  contour(axis_handle,...)

Finally, the contour command returns a handle to the newly returned contour plot. 

  handle = contour(...)

To place labels on the contour plot, use the clabel function.

Example

Here is a simple example of a contour plot with the default x,y coordinates: 
--> [x,y] = meshgrid(linspace(-1,1,25),linspace(-2,2,30));
--> z = x.*exp(-x.^2-y.^2);
--> contour(z)

which results in the following plot

Here, we specify the x and y coordinates explictly 

--> contour(x,y,z)

note that the axis limits have changed appropriately

By default, contours are created at values selected by FreeMat. To provide our own set of contour values (asymmetrically about zero in this case), we supply them as 

--> contour(x,y,z,[-.4,0.,3])

which is here

Also be default, contour uses the current color map and clim limits to determine the coloring of the contours. Here, we override the color spec so that we have all black contour 

--> contour(x,y,z,'b-')
Warning: Newly defined variable nargin shadows a function of the same name.  Use clear nargin to recover access to the function

which is here