MA/CS 371 - Lab 0
Introduction to Computing with MATLAB

Section 1: Introduction

Make sure you have the following materials. Hard copies will be available in lab. Please do not print a copy of these or any other materials in the lab - the printer in the lab is intended for the use of the lab staff and TAs.

The goal of this lab is to introduce you to:

This lab is mainly for new users who have not had previous experience with the computer environment in the CS department. Users who are already familiar with a Web browser, UNIX, a text editor, and MATLAB may skip to Section 6 (shipping the files for this lab into your account) and from there to the extra credit problems. I'd appreciate it if you would move to a computer in the back of the lab if you do so. Users who are familiar with everything except MATLAB are encouraged to do the commands in Section 6 and then play around with MATLAB while the rest of the class catches up to you. Read the MATLAB Primer, start up MATLAB (just type 'matlab' at your UNIX prompt), and maybe write some small programs or type 'demo' at your MATLAB prompt and play around. Keep in mind that this is a problem-solving course. It is not primarily a course on how to program in MATLAB. You are responsible for learning how to use MATLAB sufficiently well to deal with the problems presented in future labs. If you are not comfortable with programming in MATLAB after this lab, please take the time to become comfortable before next week. Seek help from your classmates or the TA if necessary.

Please read this lab thoroughly. New users are strongly encouraged to complete the practice problems as a measure of how well they have learned basic UNIX and commands.

Section 2: Lab Policies and Etiquette

Section 3: Logging in for the first time and the X Window System

In this section you will learn how to "log in" to a workstation and invoke X Windows.

Note: Whenever you type a command at the prompt, you must conclude the line by hitting the Return key.

  1. To start, you should see a prompt with the name of the machine followed by "login: ". If the screen is blank, hit Return or move the mouse around to get the login prompt to appear. Make sure the computer and monitor are both switched on.
  2. At the login prompt, type in your username. At the resulting "Password: " prompt, type in your password. Your password will not appear on the screen as you type it. Note that UNIX is case sensitive - capital "A" and lower-case "a" are different characters.
  3. After about 10 seconds, the machine will ask you what printer you wish to use. Respond by typing
  4. For this time only, type the following command exactly (including the tilde and the slashes):

    The above command will copy some files for your account to make it easier for you to use. This command will take a short while to process. If any messages appear (other than your next UNIX prompt), ask for help before proceeding. After the UNIX prompt re-appears, type
    which will log you out.
  5. At the login prompt, repeat step 2. You should see:
    	Last login: ...
    	Xwindows? (^C to interrupt)
    From now on the machine will go automatically into X Windows when you log in.

    The screen should now go black or speckled and "windows" will slowly start to appear - a clock, a mailbox, and then four rectangular windows. The whole process may take half a minute.

  6. The mouse is the white thing on the silver pad to the right of the machine. You will see a cursorsomewhere on the screen that moves around on the screen when you move the mouse. The cursor usually looks sort of like a capital I or a crosshairs. The way your windows work is that you can only type into a window when the cursor is inside it.

Section 4: The Netscape Web Browser

If you are not already doing so, at this point you should start up the Netscape Web browser and view this file. If you've never used Netscape before, type in the exact string below:
The first thing that will happen is you will get a copyright disclaimer box on your screen. (If all you get is a ghostly-looking rectangular border, move the cursor until the border is where you want the new window to go and press the left mouse button.) Press the 'accept' button. After your computer's hard drive churns around for a little while, you should see another empty rectangular border on your screen. Position this box in a convenient part of your screen and press the left mouse button. Netscape will then open its window on that spot.

Navigating in Netscape is fairly simple and intuitive. Use the scroll bar on the right to move around on the current document. Clicking on any of the underlined items will open up the page that they "point" to. Find the entry in this document for "Lab 0", click on it, and you should see this lab assignment!

In the future I'm not going to make a lot of hard copies of the lab assignments, so you should get used to reading the lab assignments on the computer with Netscape. It's the wave of the future.

Section 5: The UNIX Operating System

In lab we will briefly discuss some basic UNIX terminology (files, directories, pathnames) and the most frequently used UNIX commands. Refer to the Useful UNIX and vi Commands handout for more detailed explanations.

Section 6: Shipping files for this lab

When you did the setup command in Section 3, a directory called cs371 was created in your home directory. Now it is time to make a subdirectory for this lab and copy some files from the cs371 account into it. Do the following and don't forget the period at the end of the fourth command:
	cd ~/cs371
	mkdir lab0
	cd lab0
	cp ~cs371/lab0/* .

Section 7: The vi editor

The way you will often get information (especially MATLAB programs) into the machine is to type it in using an editor. If you don't know how to use any UNIX text editor, you will learn how to use vi (the name stands for visual.) vi has two modes (ways of interacting with you), the command mode and the insert mode. In the insert mode, the characters you type appear on the screen as part of the file. They are "inserted" into the file. In the command mode, the characters you type cause things to happen to the information already in the file. It is important that you understand the difference. When you enter vi, you are automatically in the command mode. Once you get into the insert mode, you can return to the command mode at any time by depressing the Esc key (top left of the keyboard). The letter "i" is one of several letters that allow you to enter the insert mode from the command mode. The best way to learn vi is to use it, so let's edit a file that contains my favorite poem.

  1. Move to the left window.
  2. Invoke vi on the file containing my favorite poem by typing
    	vi raven
The file raven should now be displayed on your screen. Remember that you are in the command mode within this window. Please pause here. As soon as everyone is caught up, we will go through some vi commands together. Meanwhile, look through the first three sections of the Useful UNIX and vi Commands handout and review what you have done so far in the lab.

Section 8: Running MATLAB and using M-files

At this point, invoke MATLAB by typing matlab at your UNIX prompt. It might be a good idea to exit vi in your main window and use the main window to run MATLAB. As MATLAB starts up, it flashes a little 'splash screen' onto your screen, and then will show a header and a MATLAB prompt which looks like this:
That prompt is the sign that MATLAB is ready for input.

At this point, bring up vi on the sample MATLAB file in your directory by doing

	vi mach_eps.m
Note that all regular MATLAB programs have the '.m' file extension, just like C programs use '.c' and FORTRAN programs use '.f'.

The file mach_eps.m is an example of a MATLAB script file. If you type mach_eps at your MATLAB prompt, each line from the file mach_eps.m will be passed into MATLAB and treated as if you had typed it at the command line. Note that each line beginning with a percent sign (%) is a comment and has no effect. (You can read more about MATLAB script files and MATLAB function files in Sigmon's MATLAB Primer.)

Go ahead and type mach_eps now. MATLAB should report the following error:

??? value = 1:
Missing operator, comma, or semi-colon.

Error in ==> /a/duncan/jade/homes/cs371/lab0/mach_eps.m
On line 11  ==> value = 1:
On simple programs, MATLAB usually does a pretty good job of pointing out where an error occurred. In this case, the line
	value = 1:
is not a valid MATLAB command.

At this point, go into your vi window, edit that line so that it is a valid MATLAB command setting the variable value to 1 without displaying anything, and make sure to save the changes to mach_eps.m. Now go ahead and type mach_eps at your MATLAB prompt again. You should get the output:

machine_epsilon =

Let's review the material that you will be expected to know after this lab:
  1. How to log in
  2. Simple UNIX commands and terminology - files, directories, copying and moving files, navigating around in your file system
  3. Viewing documents with Netscape
  4. Editing files with vi or some other editor
  5. Running MATLAB and simple MATLAB terminology (essentially the contents of Sigmon's MATLAB Primer)
  6. How to edit a MATLAB program (an "M-file") in one window and run the current version on MATLAB in another window
  7. How to log out

Appendix: Logging out

Be sure at the end of each lab session (and every other time you use a public UNIX machine) to log out! If you don't, an unscrupulous user could destroy all your files, send e-mail to people masquerading as you, etc.

To make sure you log out safely at the end of a session, you should do the following:

  1. Exit all application programs (things like MATLAB, your text editor, Netscape, and so on). Remember to save changes whenever appropriate - for example when exiting vi.
  2. Move your cursor to a spot on the "background" - in other words, a place on your screen where there is no window. Your cursor should look like a fat letter "X" when it's over the background.
  3. Press and hold the left mouse button. A pop-up menu should appear with "twm" at the top and "EXIT X WINDOWS" at the bottom.
  4. Pull the mouse down, while holding down the left button, until "EXIT X WINDOWS" is highlighted.
  5. Release the mouse button.
At this point your computer's hard drive will chatter and X Windows will clean up and exit. Our accounts are set up so that you should be logged out at this point. Make certain that you see the "cetus login:" prompt before walking away from the computer! If you see a UNIX prompt on the screen, type logout to finish logging out.

This week's questions

This week's questions will not be handed in or graded, but you should be sure you can answer them all. If you have any difficulty with the questions you should take the time to practice before next week's lab.

Extra Credit MATLAB problems