# Help and other tools

## Places to get help:

• Typing "help" at the matlab prompt gives you a list of all the possible directories matlab can find commands in (which also tells you its "search path", or a list of the directories it is looking in for commands.)
• Typing "help directoryname" gives you a list of the commands in that directory and a short description of them.
• Typing "help commandname" gives you help on a specific command.
• Typing "lookfor keyword" gives you a list of commands that use that keyword. ie, "lookfor integral" lists commands that deal with integrals. It's pretty slow, choose the word wisely. You can use control-c to stop searching when you think you've found what you need.
• Typing "doc" starts up a web browser with the Matlab on Athena home page. This includes the entire reference manual for matlab, a whole lot of other information on using matlab, and a pointer to the Matlab Primer, a good introduction to using Matlab.
• You can get copies of "Matlab on Athena" at Graphic Arts. You can also get copies of the Matlab Primer mentioned above. (There's a small fee for copying costs on both.)
• The matlab manual and manuals for many of the toolboxes are available in some clusters and can be borrowed from the consultants' office in 11-115.

## Some Useful Tools:

• If you accidentally reassign a function name to a variable (ie, you try saying sum = 3 and then you get errors when you try to use the sum function because it doesn't know it's a function anymore), you can restore it to its normal state using "clear functionname". You can also use clear to get rid of all variable values with "clear all".
• `who`
will tell you all the variables you have currently defined.
• `whos`
will tell you the variables, their sizes, and some other info.
• `pi`
is a function of that returns the value of pi.
• `eps`
is a function that returns Matlab's smallest floating point number. This is useful if you have a vector that might contain zeros that is going to wind up in the denominator of something. If you add eps to the vector, you aren't actually adding anything significant, but you won't run into divide by zero problems anymore.
• `format long`
and
`format short`
switch between the long and short display format of numbers. Either way matlab uses the same number of digits for its calculations, but normally (format short) it will only display the first four digits after the decimal point.
• Typing
`type`
functionname for any function in Matlab's search path lets you see how that function is written.