help

Purpose

Online Help for MATLAB functions and M-files.

Synopsis

help
help topic

Description

help, by itself, lists all primary help topics. Each main help topic corresponds to a directory name on MATLAB's search path.

help topic gives help on the specified topic. The topic can be a function name or a directory name. If it is a function name, help displays information on that function. If it is a directory name, help displays the contents file for the specified directory. It is not necessary to give the full pathname of the directory; the last component, or the last several components, is sufficient.

You can write help text for your own M-files and toolboxes; see the following sections for more information.

Algorithm

MATLAB's Help system, like MATLAB itself, is highly extensible. This means that you can write help descriptions for your own M-files and toolboxes - using the same self-documenting method that MATLAB's M-files and toolboxes use.

help, by itself, lists all help topics by displaying the first line (the H1 line) of the contents files in each directory on MATLAB's search path. The contents files are the M-files named Contents.m within each directory.

help topic, where topic is a directory name, displays the comment lines in the Contents.m file located in that directory. If a contents file does not exist, help displays the H1 lines of all the files in the directory.

help topic, where topic is a function name, displays help on the function by listing the first comment lines in the M-file topic.m.

Creating Online Help for Your Own M-Files

You can create self-documenting online help for your own M-files by entering text on one or more contiguous comment lines, beginning with the second line of the file. (See the MATLAB User's Guide for information about creating M-files.) For example, the M-file angle.m provided with MATLAB contains:

function p = angle(h)
% ANGLE Polar angle.
%    ANGLE(H) returns the phase angles, in radians, of a matrix
%    with complex elements. Use ABS for the magnitudes.
p = atan2(imag(h),real(h));

When you execute help angle, lines 2, 3, and 4 display. These lines are the first block of contiguous comment lines. The help system ignores comment lines that appear later in an M-file, after any executable statements, or after a blank line.

The first comment line in any M-file (the H1 line) is special. It contains the function name and a succinct description of the function. The lookfor command searches and displays this line, and help displays these lines in directories that do not contain a Contents.m file.

Creating Contents Files for Your Own M-File Directories

A Contents.m file is provided for each M-file directory included with the MATLAB software. If you create directories in which to store your own M-files, you can create Contents.m files for them too. To do so, simply follow the format used in an existing Contents.m file.

Examples

The following command gives help on the demos directory:

help demos

To prevent long descriptions from scrolling off the screen before you have time to read them, enter more on; then enter the help command.