MATLAB has an extensive help system built into it, containing detailed documentation and help information on all of MATLAB's many commands and functions. This help system is extremely useful for beginners to MATLAB, but even after becoming an expert at MATLAB, you will still use the help system often to refresh your memory of the details of particular MATLAB commands and functions. This lesson will show you how to use the MATLAB help system. 


There are two equivalent ways (i.e., both ways access the same underlying information) that you can access the MATLAB help system. The first is simply to type at the command prompt in the MATLAB command window "help" followed by the name of the command or function for which you want help. Doing this will then present you with some text describing the MATLAB command or function you typed. Here is how you access the help information for the date command.


help date

DATE Current date as date string.
S = DATE returns a string containing the date in dd-mmm-yyyy format.



Notice how it also tells you "See also NOW, CLOCK, DATENUM" after giving you the help information for "date". These are related MATLAB commands or functions, and you can access their help information in the same way (i.e., "help now", etc.) In general, when returning help information about some command or function, MATLAB will also suggest similar commands or functions in this way. Go ahead now and try using the help command; type "help date", "help now", and even "help help" (there is even help information for the help command itself!) at the command prompt.


Getting Help a Screenful at a Time


You probably noticed that when you typed "help help" at the command prompt, the help information that was returned to you was too long to fit on one screen, and thus what you ended up with in the MATLAB command window's screen was only about the last half of the help information for "help". You could just go to the beginning of the help text by using the scroll bar at the right side of the window, and scrolling up to the beginning of the returned help text. However, it would be nice if there were some way you could have MATLAB return the information to you one screen at a time; then, after reading one screenful of the help text you could just hit a key on the keyboard and move on to the next screenful. Happily, there is in fact a way to do this with the "more" command. The way it works is as follows. If you type "more on" at the command prompt, then all help information returned after that will be presented in readable, screen-at-a-time chunks (with the text "--more--" at the bottom); pressing the space bar will then move you to the next screenful of help text (i.e., it will give you "more" text), while pressing any other key will move you on to just the next line of help text. Typing "more off" at the command prompt will revert to the default behavior (i.e., all help text will be presented at once, and you will have to scroll back to the beginning for some long help texts.) Go ahead now and try using the "more" command; type "more on" and then "help help" and then the space bar or other keys to progress through the help text.


Functional Categories


An important thing to note is that MATLAB groups all commands and functions into various functional categories. For example, there is one functional category called "timefun" and the "date" and "now" commands are members of this functional category. If you just type "help" by itself at the command prompt, you will get a list of all of MATLAB's functional categories (called "HELP topics" below):



HELP topics:

matlab\general - General purpose commands.
matlab\ops - Operators and special characters.
matlab\lang - Programming language constructs.
matlab\elmat - Elementary matrices and matrix manipulation.
matlab\elfun - Elementary math functions.
simulink\simdemos - Simulink demonstrations and samples.
simulink\dee - Differential Equation Editor
toolbox\local - Preferences.

For more help on directory/topic, type "help topic".


In addition, you can get help information about a particular functional category, and its member commands and functions, by simply typing at the command prompt "help" followed by the name of the functional category. For example, typing "help timefun" will give you information about the "timefun" functional category:

help timefun

Time and dates.

Current date and time.
now - Current date and time as date number.
date - Current date as date string.
clock - Current date and time as date vector.

Basic functions.
datenum - Serial date number.
datestr - String representation of date.
datevec - Date components.

Date functions.
calendar - Calendar.
weekday - Day of week.
eomday - End of month.
datetick - Date formatted tick labels.

Timing functions.
cputime - CPU time in seconds.
tic, toc - Stopwatch timer.
etime - Elapsed time.
pause - Wait in seconds.


Searching for Commands


Another important command for accessing the MATLAB help system is the "lookfor" command. Recall that "help" will display the help text for some command or function, but you have to know the exact name of the command or function in order to be able to get this help text. What if you don't have any particular command or function in mind, or don't know the exact name, but rather would like to get a list of all commands or functions related to some word? This is precisely what the "lookfor" command can do for you. At the command prompt, you type "lookfor" and then a keyword, and MATLAB will search the help texts of all commands and functions. Any command or function whose first line of help text contains the given keyword will be returned by the "lookfor" command. You should be warned, however, that the "lookfor" command can take a long time to complete. As an example, typing "lookfor sine" returns the following:


lookfor sine
SIN Sine.
SINH Hyperbolic sine.
COS Cosine.
COSH Hyperbolic cosine.
ASINH Symbolic inverse hyperbolic sine.
DCT    Discrete cosine transform.
IDCT    Inverse discrete cosine transform.


Opening up a Separate Help Window


The second way to access the MATLAB help information is more graphical and windows-oriented. It allows you to open up a separate window (the MATLAB help window) in which you can view and navigate through the help information by typing command names, clicking buttons, selecting text, etc. You can open up this help window by either typing "helpwin" at the command prompt, or by selecting "Help Window" from the "Help" menu at the top right side of the MATLAB command window. The MATLAB help window will look like this, and will initially contain the list of all the functional categories:



You can then see the help information for a particular functional category by double clicking the mouse on the text of the functional category in the help window. For example, double clicking the line containing the text "matlab\elfun" above would give you the help information for the "elfun" functional category. Then, you can double click particular commands and functions in the chosen functional category to get help information for them. You can navigate to previous screens by clicking the "Back" button, and then back to where you were by clicking the "Forward" button; clicking the "Home" button takes you to the initial screen (with the list of all functional categories). If you type a functional category, or a command or function name, into the text box at the upper left (i.e., the one that says "MATLAB Help Topics" above) and then hit return, you will get the help information for it. Finally, the place where it says "see also" above is a menu from which you can select related commands and functions, and get help information for them. At the command prompt in the MATLAB command window, you can also just type "helpwin" followed by a functional category or command or function name to have the MATLAB help window open up with the help information for that functional category or command or function.


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