General Computing Questions


Can I work from my room if I have cactwin?

Yes, but use the basic Telnet terminal program (mine is EWAN, but I don't think that's in the default package). Don't use the 3270 terminal program. Connect to one of the ECSEL machines such as avenger.ecsel.psu.edu. For our purposes you may find that the older cacslip package provides a better terminal emulation.

How do I get on from a computer lab? What computer labs can I use?

This varies from machine to machine. On Mac's look for NCSA telnet and open a connection to one of the ECSEL machines (e.g. avenger.ecsel.psu.edu). If Windows is up on the PC look for an Internet Access group and see the previous question on cactwin. If the PC is in it's initial menu state go to Windows, or look for a menu item with terms like "communication," "telnet", "internet connection." March through until are asked for a host address, to open a host, or open a connection, and give it an ECSEL machine address such as avenger.ecsel.psu.edu. You should be able to use any CAC lab for general work. Nearby labs include Waring Commons, 15 Sparks and 6 Willard. If you login to PSUVM the command "help labs" will give you more information.

What spreadsheet should we use?

Whatever you have available. I recommend Excel, Lotus123, or Quatro Pro.

How can I converse interactively with another user?

On most Unix machines you can do this with a utility called "talk" ( use man for more information).

How do I mail Lotus or Excel output?

The first step is to save your spread sheet results as a text file. In Excel the SAVE menu has an option in the lower left corner "Save file as Type". Choose "Text" from the options in this sub-menu. Something similar exists in Lotus, but I don't have the program in front of me. Put this text file on a floppy disk and take it to a CAC lab machine and follow my instructions in the homework submittal for running ftp. If you have CACTWIN, you can use the FTP icon to do the same type of move to the ECSEL machines.

Why is it hard for me to use the arrow keys from my machine off campus?

Two possibilities. Make sure you try the command to Unix "set term=vt100". If that doesn't fix the problem you have a poor terminal emulator or need to fix something called the "keyboard map" associated with your terminal software. The biggest use for arrow keys are in vi. Run through the tutor.vi exercise and learn how to use letter commands to handle most of this work.

Exactly what is avenger Ecsel, Unix, and vi?

For our purposes "ecsel" is a cluster of workstations and PC's (a sub-network) in 305 Hammond. Avenger is a specific IBM RS6000 workstation sitting in 305 Hammond. Unix is the operating system (actually just another computer program) that controls the actions of Avenger and many other machines. vi is a special purpose program that comes with Unix, that lets you make your own files, including Fortran program files.

How do I send you an Excel Spreadsheet, that I have on a Mac?

Take the easy out and print the spreadsheet in a Mac Lab, and give me the hardcopy, or see ftp below.

How do I use ftp?

Here is an example connecting to a PC (probably the one you are using as a terminal).

%ftp 128.118.771.81 Use ftp to pick up a spreadsheet

Connected to 128.118.771.81 file from a floppy on the lab PC

220 128.118.771.81 FTP server (SunOS 4.1) ready.

Name (ajb123):

331 No Password required for ajb123.

230 User ajb123 logged in.

ftp> cd a: This connects to the floppy drive

250 CWD command successful.

ftp> get spread.data This file must be in Text format

200 PORT command successful.

150 ASCII data connection for swiss (146.186.125.12,1135) (55292 bytes).

226 ASCII Transfer complete.

56107 bytes received in 0.4001 seconds (136.9 Kbytes/s)

ftp> quit

221 Goodbye.

Here is an example of working between the CAC Sun's and the Ecsel machines. I start from farman.cac with the intention of bringing in a file from avenger.ecsel. Note that I must login as myself on avenger, giving someone else's user ID requires also giving their password. If I want to pick up a file from user abj123, I login as myself, then issue the command "cd ~abj123" to change to abj123's home directory. If the file I need has read access privileges I can get it. If the file is in a subdirectory, I can get there with another cd command.

curtiss.101> ftp avenger.ecsel.psu.edu
Connected to avenger.ecsel.psu.edu.
220 avenger.ecsel.psu.edu FTP server (Version wu-2.4(2) Sat Feb 11 12:38:13
EST 1995) ready.
Name (avenger.ecsel.psu.edu:jhm): 
331 Password required for jhm.
Password:
230 User jhm logged in.
ftp> ls -FC			 Look at files on avenger
200 PORT command successful.
150 Opening ASCII mode data connection for /bin/ls.
bin/           hw8/           newton1.f      questions.wp   trig.output
cannon.wp      iftests.f      o.cshrc        tedi.ini*      trig3.f
factorial.f    inter1.f       o.forward      test/          tutor.vi
homework/      inter2.f       old.cshrc      test.f
hw3-in/        mbox           outline        trig.f
226 Transfer complete.
ftp> get newton1.f	 Bring the file "newton1.f onto farman
200 PORT command successful.
150 Opening ASCII mode data connection for newton1.f (1160 bytes).
226 Transfer complete.
local: newton1.f remote: newton1.f
1205 bytes received in 0.062 seconds (19 Kbytes/s)
ftp> cd test		 Change to subdirectory "test" on avenger
250 CWD command successful.
ftp> put good.f		 	Copy the file "good.f" from the current
directory of farman into the "test" directory of
avenger.
200 PORT command successful.
150 Opening ASCII mode data connection for good.f.
226 Transfer complete.
local: good.f remote: good.f
610 bytes sent in 0.033 seconds (18 Kbytes/s)
ftp> quit

You should also know the ftp commands: "?" for help; "mget" to put multiple files using the "*" wildcard; and "mput" to put multiple files. "mget *.f" gets all files having names ending with ".f".

Why does vi work so badly from off campus?

Either you have not issued the "set term=vt100" command, your terminal software does not support vt100 emulation, or you have a poor mapping of keys in your terminal software. I never have trouble with KERMIT, CACSLIP, or CACTWIN, all available free from the CAC. Stop by my office for more advice.

vi is a major pain, what can I do?

Some students are successfully using MicroSoft Word on PC's and Macs. This option of requires changing your files on a PC and moving them to Unix machines with ftp. Two other options are to learn the "emacs" editor or the "xedit" editor.

How do I designate my own printer as the destination for printout?

I don't have any clean answers for this one. In the above example of ftp to a PC, if I did a command "put hw4.f PRN" it would route the file on the Unix machine to the printer on an IBM compatible PC. Generally you are reduced to moving the file to the PC with ftp and using a local PC print command to print the file.

Why does Avenger have compilation problems with messages like "insufficient space"?

Avenger suffers from disk space problems from time to time. You can either clear out un-needed files or move to the other cluster of machines.

If we type "users" on the ECSEL machines, how many people is max for efficient operation?

I don't have an answer for that. It depends on what the users are doing (I have machines that saturate with 2 people running system simulations). The best you can do is run users regularly and develop statistics. I will pass on any comments from class members on average performance versus number of users on the machine.

I missed the Sreadsheet Lab. Could you list some major points I should look for.

The first thing to do is check the items on the HELP menu. One or two of them are usually pretty good self help tutorials for the SpreadSheet (the items usually contain words like "Introducing" or "Learning"). Sit down at a spread sheet, use the mouse to point at the cell (box) in the upper right corner (column A, row 1) and type in a number followed by a return. This cell is named "A1". Do the same thing in the cell below (A2). Now point to A3 and type "=A1+A2", followed by a return. What happens? Beginning your entry with "=" signals the spread sheet that you are entering a formula to be evaluated. In cell A4 try entering "=sum(A1:A2)". Use the help, play for a while, and stop by my office if you have questions. If you want to try something tricky with EXCEL, I may be able to help, or can guide you to the right information in my manual set.

I still don't understand how you can Design a program to use pipelining.

The full answer to that question takes another 2 or 3 courses. The starting point is to group calculations so that the same thing is done for a large group of array elements with no dependence on the results of any other calculations in the group. In this grouping you want to minimize the number of IF tests. Too many of these, and a compiler will give up trying to vectorize. As you get more experience in problem solving with computers, you will discover that this is not always easy, and at times you have to rule out one solution method in favor of another less elegant one to get best computational speed. I'm not trying to turn you into a pipelining expert, just trying to show you where to start looking for extra speed.

I'm still having trouble with ftp.

If you've tried all of my samples in past answer sheets, it's time to sit down with me at a PC.

What is Mathematica?

It is a mix of computer language, expert system, and symbolic algebra. Languages like Fortran, C, and Pascal really only deal with numbers and simple character manipulations in any easy way. Getting Fortran to solve the equation Ax3+Bx2+Cx+D=0 for x in terms of the symbols A, B, C, and D (no numbers assigned to A, B, C, or D) is a major programming effort. Mathematica does the job with a single command:

Solve(A*x^3+B*x^2+C*x+D==0,x). A similar situation exists for factoring the expression x2+x-12, and a large number of other related problems that have been inflicted on you over the years in math and science. Although people rarely explain it to you, such problems continue to crop up throughout your professional life, and programs like Mathematica are useful tools for speeding your manipulation of equations, and double-checking hand done algebra and calculus.

Can you provide a list of Mathematica commands?

You have a short list on the Web page. Take a look at my "mathin" sample file for examples of a few. I am treating Mathematica the same way that I am treating Spreadsheets. You need someone in the group to use it (or Mathcad) for cross-checking homework, but are not responsible for knowledge of the tool on an exam. I hope that many of you will see the advantage of the tool for helping get through homework in a wide range of classes. With sufficient demand I'm willing to run some side labs on the subject or set you up with a Mathematica tutorial.

I have Mathcad on my PC. Can I use it instead of Mathematica?

Yes. It will probably be best for you to just give me a copy of the Mathcad printout.

Why do Mathematica commands start with a capital letter?

That way if you stick to all lower case letters on the variables you define within Mathematica you won't trip over Mathematica commands or internal Mathematica variables and functions.

How do you wrap around long equations in Mathematica?

Pick a point where the equation is obviously not complete (right after a +, - *, ^, or before all parentheses are balanced), hit the RETURN (ENTER) key and keep going. Mathematica will figure out what you are doing. The other method is to just type a "\" before the RETURN (ENTER) key.

Why can't you backspace on the Sun's

Sun and IBM disagree on the control character (special key) that is appropriate for a backspace. Generally if the Backspace key is working for the IBM's (ECSEL) the Delete key or Control-Backspace) will work for Sun. On many campus terminals it's the other way around, a simple backspace key working for Sun and the Control-Backspace working for IBM. If all else fails try the following procedure. At the Unix prompt type "stty erase" followed by a space, followed by hitting the key that you want to work as the backspace, followed by hitting the RETURN (ENTER) key.

Are there other Internet goodies besides NETLIB?

Yes, NETLIB is one of hundreds of public repositories for computer programs. It happens to be the best maintained and most relevant to our disciplines, but you should not restrict your searches there. I'll leave it to you to learn how to use the Web (Mosaic, Netscape, etc) search engines. They are relatively simple and self-documented. I will introduce you to an older site searcher called "archie" that may also by useful and can be used from any dumb terminal.

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Maintained by John Mahaffy : jhm@cac.psu.edu