# 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.

## See Also

    dir, lookfor, more, path, what, which

(c) Copyright 1994 by The MathWorks, Inc.