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SF State PHYS 385 - Using the P&A Computer System

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Vector Spaces in Physics 8/16/2014 B - 1 Appendix B. Using the P&A Computer System The Physics and Astronomy Department maintains a rather complete computer system for use by P&A faculty and students, located in TH 124. There are about 10 PC's running Linux, and several others running Windows. The Linux machines are typical of the platform used by many scientists for calculation. They should all have MatLab, Pyghon, IDL and Mathematica installed locally. The information given below is rather volatile, since the computer system is currently in a rapid state of change [written August 24, 2009.] Up-to-date information on this system can be obtained over the web at http://www.physics.sfsu.edu/compsys/compsys.html 1. Logging on. To use the Physics and Astronomy computer system you need a system account. Your instructor should request it, and when it is set up, you need to go to the Department office to get your password, and to ask Peter Verdone (TH 104 or TH 212) for a PIN to get you into TH 123. (If you have the password, a teacher or fellow student will probably let you into the room, on a temporary basis.) We will assume that you have your password and can get into TH 123. (1) Choose one of the Linux machines. Pressing [enter] brings up a prompt for entering your user name and password. A first-time user may receive some startup messages. (2) A desktop should open. If you only get a command window, start the desktop by entering the command startx. (3) From the desktop, open a terminal window by clicking on the third icon from the left on the task bar at the bottom of the screen. (4) I prefer to work from x-terminal windows. To open one of these, enter (from the command line of the terminal window) th123-22:bland% xterm & NOTE: the first part of this instruction, th123-22:bland%, represents the command-line prompt, and you do not type it. It will have your name, not bland. The command "xterm" should open another window. The "&" character at the end of the line detaches the xterm window from the window executing the instruction. Otherwise the terminal window is useless as long as the xterm window is open. 2. Running Mathematica, MatLab and IDL. You should be able to run these programs natively on all of the machines in TH123, Linux or Windows. If your machine does not seem to have Mathematica, it might help to connect to some other machine. For instance, to connect to th123-21, enter th123-22:bland% ssh th123-21 Next, check to see that X-windows communication is open by running the clock window: th123-21:bland% xclock &Vector Spaces in Physics 8/16/2014 B - 2 A small window with a clock face should appear on your desktop. If it does not, something is wrong. If xclock worked, you can run one of the big computation programs. th123-21:bland% MatLab & th123-21:bland% IDL th123-21:bland% Mathematica All of this can be done from Windows, too. You need to run an X-windows host, such as xwin32 or xming, then connect to th123-22.sfsu.edu using a secure shell application such as SSH. (See the Department computer system site, http://www.physics.sfsu.edu/compsys/compsys.html, for more information.) Once connected, open an xterm window, and continue as above. You will find that many operations take a lot longer this way, due to the network connection. And with Mathematica there are often problems with fonts. I recommend that you start the semester working in the computer room, and set up remote access later if you want. 3. Mathematica. This section gives some details on using Mathematica. Follow these instructions to load and execute Mathematica. One warning - you may have to turn the "Num Lock" selection off for Mathematica to respond to the keyboard. th123-22:bland% mathematica & A Mathematica icon should appear at once in the lower left-hand corner of the desktop, and in a few seconds a Mathematica window will open. If instead you receive a message telling you that the proper fonts are not installed, something is wrong. Try moving to another workstation. Here is a Mathematica command to enter, just to make sure that it is working: Plot[Sin[x], {x, 0, 4 Pi}] Execute the instruction with [shift][enter]. (Just pressing the [enter] key moves to a new line, but does not execute the instruction.) A graph of two cycles of a sine wave should appear. To use the function for vector addition discussed in the text, carry out the following commands from a terminal window: th123-22:bland% ls Shows files on your home dir. th123-22:bland% mkdir 385 Create directory for Ph 385 th123-22:bland% cd 385 Change to Ph 385 directory th123-22:bland% cp ~bland/export/385/vectsum2.nb . (Note the space and period at the end of the line.) th123-22:bland% ls Should show the file vectsum2.nbVector Spaces in Physics 8/16/2014 B - 3 Now you can open the file vectsum2.nb with Mathematica and do the vector-addition exercises. If you prefer to work from home, and if you have Mathematica on your own computer, you can download the file vectsum2.nb from the download page on the course website and work on it


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