|Starting up Matlab||Exercise 3|
|Using a USB drive|
|Using a browser to download files|
|More on Matlab|
This lab will occupy today's lab session only. This session will introduce the mechanics of using Matlab, particularly on the Linux computers here in the lab. There is some reading to be completed before the second session and you can do that here in the lab or at any other computer with web access. The second lab, two sessions long, will present exercises in Matlab use.
The discussion that follows assumes that you are basically familiar with using a Unix-like operating system such as Linux and browsing the Web. The next few sections will give a brief introduction to Matlab and explain how to use it and those aspects of the environment that will be important to doing the labs.
The labs roughly follow the material presented in lecture, but are independent of the homework and other exercises presented in lecture. Lab grades count as 30% of your course grade.
Attendance is not required, but help is most readily available during the lab sessions.
You are encouraged to work together with other students, but you must provide your own diary and summary files (explained further below).
Each lab will be given a grade of A+, A, B, C, or 0. These grades correspond with percentage grades of 100, 95, 85, 75, and 0. At the end of the semester, your grades will be averaged and then integrated with your grade in lecture. The grading criterion is:
|A+||100||The work is correct, or there are only very minor errors.|
|A||95||All exercises were attempted and are substantially correct.|
|B||85||All exercises were attempted but there are some serious errors.|
|C||75||Substantial portions of some exercises were omitted.|
|Zero||0||Lab was not submitted.|
Some of the labs include extra credit exercises. The percentage value of these extra credit exercises are stated with the exercises themselves. At the end of the semester, the extra credit percentages will be added to the grade percentages and the average computed from the sum, except that averages will not exceed 100. Half of the unused extra credit on one lab will be applied toward later labs. Unsubmitted labs will not be eligible for extra credit.
Each lab is due before 11:59 PM the day the subsequent lab begins. Labs submitted after the day the subsequent lab begins will have 1% deducted from the percentage grade for that lab. An additional percent will be deducted for each further week they are late. The final due date for labs 2 through 7 is the last day of classes for the semester, and the final due date for labs 8, 9 and 10 will be announced near the end of the semester. Labs that are not submitted before their final due date will be given a grade of zero, except under special circumstances.
Matlab is available on the computers in GSCC 126 and on the computers in the labs in Thackeray hall, such as the seventh floor computer lab opposite the lounge. Matlab is also installed in computers in other labs at Pitt, and you can purchase it for your personal computer from the university software center for a nominal fee.
In this section you will see how to start up of Matlab using the Java windowing interface. These instructions are the same for Unix, Mac and MS-Windows versions of Matlab. I will also give the command-line equivalents of many of the commands. These command-line equivalents are valid for all versions of Matlab as well as for the Matlab clone named Octave. Generally speaking, anything you can do using a menu can also be done with command-line equivalents. You would use the command-line equivalents when writing scripts and the menus when working interactively.
Sometimes, the window will open up containing a large number of warning messages about files missing. These messages are ``normal'' and can be safely ignored.
The default window is divided into a larger pane on the right, and two panes, each with identification tabs at the bottoms, on the left. The right windowpane is a command windowpane and you will be typing Matlab commands in it. On the left side of this command windowpane somewhere (near the bottom in the figure) there will be a prompt of the form ». Your typed commands go next to this prompt.
There are two choices for display on each of the two windowpanes on the left. I suggest that you choose ``Workspace'' on the top and ``Command History'' on the bottom in general, although we will have occasion to use ``Current Directory'' on the bottom.
Warning: You must switch to one of these directories or some other permanent directory each time you start Matlab. It is easy to forget to switch and if you do forget and log off from the computer, your work will be lost! In that case, your ``Command History'' will be retained and you can use it to help reconstruct your work.
If you wish to use the command line to create and switch directories, you can switch to your permanent ``AFS/private'' directory with the ``change directory'' commands
cd Desktop cd AFS cd privateYou create a directory named math2070 with the command
mkdir math2070and you can make it the current directory with the command
cd math2070You can always find the name of your current directory with the command
pwdand you can get a listing of the files in the current directory with either the command
diror the command
Before going on, create the directory math2070, with subdirectories lab01, lab02, ..., lab10.
diary diary.txtThe name diary.txt is actually the name of the file that is created and you can use any name you like. It is a text file, and you should use .txt to name it. Before going on, type this command in the ``Command'' windowpane. Terminate the command by hitting the ``Enter'' key. In labs that take up several sessions, using the diary diary.txt command in the second session will append to the previous work and will not overwrite it.
You should also type a comment line that will help you identify your work later. It should start with the comment character, a percent sign %, and include the lab number and date. This line will serve as an identifier when you look at the file.
Note: The diary file contains a complete record of all the work you do in Matlab. You are to retain this complete record to send to me for grading. Please do not turn the diary file on and off or edit the diary file to hide your errors. There are times when you write an explanation that is not, in my opinion, correct and I will need the complete diary to establish what really did happen.
!zip labfiles.zip *.m *.jpg *.txtwhere ``labfiles.zip'' is the name of the file and can be chosen as you wish. (The exclamation point is necessary to tell Matlab that the command is a ``system'' command and not a Matlab command.) You then only need to attach this one file to your email. You should do this only once, when you have completed all your work and after you have closed your diary file with the same command (diary diary.txt) you used to open it, or after you have closed Matlab down and then opened it again.
The storage in your AFS area is quite limited, amounting only to eight megabytes or so. This is plenty for the work we are doing, but if you try to keep many old files or files from other courses there, you will run out of space. The computers in GSCC support using USB drives (``flash'' or ``thumb'' or ``jump'' drives or ``memory sticks'') to save your files. You can insert a USB drive into one of the USB slots and wait a few seconds. A new icon will show up on the desktop and you can double-click on it to see the contents of the drive. You can drag and drop files from other directories into your USB drive directory, thus making portable copies of your files.
You must not simply remove the USB drive from its slot when you are done! Instead, when you are ready, go to the icon on the Desktop representing your USB drive and right-click on it. Choose ``unmount'' or ``eject'' on the menu and give it a little time to get its act together. Then you may remove the drive. The reason for this rigmarole is that data do not get written immediately to the drive, but are written at the computer's leisure. Unmounting the drive forces the last data to be written. You may have noticed that MS-Windows offers the option to ``safely remove'' a USB drive, which accomplishes the same thing.
Some of the labs require that you download files from the web in order to use them. The following exercise illustrates how to download files. The file you will download is a very simple script file.
Right-mouse click on the file demoscript.m
to bring up a menu. Choose ``Save link as'' and a file save
box will pop up. Navigate to the directory you made:
and save the file with the name demoscript.m. You must use
the .m extension to tell Matlab that the file contains Matlab
commands. Return to the Matlab command window. The file should be
visible to Matlab, a fact that you can confirm with the dir
command or by its presence in the ``Current Directory'' windowpane.
Edit the file by typing the command
edit demoscript.mor by double-clicking on the file in the ``Current Directory'' windowpane, or using the ``FileOpen'' menu pick. An edit window will show up. Read through the file: the comments make it self-explanitory.
You can tell Matlab to execute (that is, cause the statements in the file to be executed) the file by typing its name, without the ``.m'', on the command line. (There is another method for executing a file that is not so appropriate for this course: you can choose ``Run'' from the Debug menu on the edit window.)
Do not be confused by the final few statements in the file. They refer to the following exercise.
The following two exercises illustrate the use of the debugging capability of Matlab. Most of the time you will be able to see what is wrong from the Matlab error messages, but sometimes the error is not obvious. In Exercise 2 below, you will see what you might do when you just cannot see why something is wrong.
dbstop if error dbstop if naninfor through the Breakpoints menu on the Edit window.
dbquitThis action will return Matlab to its usual » prompt.
dbclear allor from the debugging menu in the edit window.
Debugging (finding errors in) code you have written is the most time-consuming and least rewarding task in writing code. I am sure you think you will not be making errors, but everyone makes errors and they can be very difficult to find. You can often find your errors based on the line numbers included with Matlab's error messages, but sometimes the error remains a mystery. In that latter case, the Matlab debugger is the most powerful tool you have available.
Another important use of the debugger is for tracing through a piece of code to help you understand how it works. The benefit of the debugger used for tracing is that the effect of each statement is immediatly clear. Careful tracing is the quickest way to learn how code works.
The following exercise illustrates how you can use the debugger to trace execution. It uses the same demoscript.m file as before.
It is important to be able to get help when you need it. Matlab provides two help facilities from inside Matlab itself and a third on the web. The easiest way to get help is to use the ``Help'' menu at the top of the Matlab window. Command-line help is also available from the Matlab prompt by typing ``help command''. For example,
help diaryYou will get a short description of how to use the command. You will also get a list of related commands near the bottom of the help description, and you will often find other appropriate commands there. When you write your own Matlab files, you should always include some special comments in the beginning of the file. The comments up to the first executable statement or blank line will be printed out in response to the help command. For example, the command
help demoscriptwill give a quick help message from the first three lines of demoscript.m. You may notice that the first of these lines is included in the file listing in the ``Current Directory'' windowpane.
A second way to get help from the command prompt is the following.
helpdeskThis command brings up a comprehensive help facility, the same one that the Help menu brings up. This help facility is very similar to the one on the web from the URL:
You exit Matlab by typing quit at the command line or by using the FileExit menu choice.
You should complete a report of the results you obtained for each completed lab. This report need not be elaborate. The report consists of at least two files: the complete, original, unmodified, diary.txt file(s) plus a summary file. This summary file can be easily created as you do the lab by keeping a text file up in the editor and copying parts of the web page, your commands and output to the file as you work. Another way is to start from the diary.txt file and delete all your false starts and errors to produce a compact record. (If you work this way, do not forget to make a copy of your diary.txt file to send to me. Click here to see a sample summary file.
This summary file is very important. It is what I will read first and, if it is well-written and the work is done correctly, I will not need to read anything else. Never put incorrect Matlab statements into your summary because it will take me a lot of time to discover you really didn't mean them. I expect to see
Summarizing your work is important not only for my convenience in grading, but also to help fix in your mind the focus of each exercise.
Equally important, the summary file helps get you into the habit of keeping track of your numerical experiments in some formal manner. When you are doing research, you may be doing hundreds of numerical experiments, and you MUST get into the habit of documenting your work or you will not remember from month to month what each one did. The idea of the summary is that you can easily refresh your memory on exactly what you did to accomplish some particular task.
Here is what I want to see in the summary file:
Here is what I do NOT want to see in the summary file:
If you want to know how much detail to include, think of the following scenario. You have completed this course and, a year from now, a friend who is taking the course is having trouble. Your friend comes to you and asks how you did a particular exercise. You have saved your work, so you go look at it. The first place you will look is in your summary to see what you did. If the summary file contains only ``Exercise 1.a: complete,'' you will then have to go re-read the original lab and look for your script files, etc. Instead, the summary should describe what you did so you can explain it in general to your friend without referring to other materials. If your friend needs more detail, you can look at the other files you wrote for the lab.
Do not write a summary of the work in today's lab. Instead, please read the following information about Matlab commands from either the PC here in the lab or from another computer on the web.
The Mathworks, maker of Matlab, includes a short tutorial on using Matlab called Getting Started This tutorial is also available from the Matlab command prompt with the command helpdesk and also from the Help menu, and, if you have your own copy of the Matlab manuals, it comprises the ``Getting Started'' book.
If you feel you need more explanation of programming techniques, you may find the following reference useful.
Charles F. Van Loan and K.-Y. Daisy Fan,
``Insight Through Computing, A MATLAB Introduction to Computational Science and Engineering,'' SIAM, 2010, ISBN: 978-0-898716-91-7
The beginning of the ``Getting Started'' tutorial is the best presentation of the general capabilities of Matlab that I have come across. In order to have an overview of Matlab, read through the first sections of the tutorial. There is only the equivalent of about 100 pages of material here, mostly very easy to understand. The most important chapters are
Begin the ``Getting Started'' tutorial now, during this lab session. Read as much of it as you can now, and complete it at home or from any convenient computer connected to the web. The list of topics that follows includes topics that will be necessary for this semester's labs. The second lab addresses some of these topics, but you will be well-served if you have seen the introduction.
Back to MATH2070 page.