Xmgr Tutorial

To begin this xmgr tutorial first launch the application xmgr by typing xmgr at the Unix prompt.

The five options at the top of the xmgr main window, File, Data, Graph, Page and View, each provide extensive pulldown menus with several options. For example, left clicing on the View button produces the following options:

• Locator bar
• Status bar
• Tool bar
• Set locator fixed point
• Clear locator fixed point
• Locator props...

Each set options followed by ... have their own submenu or several associated options.To keep this introduction to xmgr short, only a few of the options in each pulldown menu will be discussed. Consult the xmgr users guide for more details.

HANDS ON 1 -- EXPLORE SOME OF THE PULLDOWN MENUS

Spend about five minutes exploring some of the options under the File, Edit and View. Be sure to explore:

• File/Read sets...
• File/Printer setup...
• Data/Transformations...
• Graph/Titles...
• Graph/Tick labels/tick marks...
• Graph/Frame...
• Graph/Symbols...
• Graph/Strings & things
• Graph/Time Stamp...

Part of the aim of performance programming is to use vector and parallel architectures to gain an increase in computational power over conventional single CPU, scalar architectures. An elementary performance programming model is given by Amdahl's Law, which in its simplest form states

speedup = 1/(1-f - f/v)

HANDS ON 2 -- PREPARE A DATA FILE FOR XMGR

In this part of the tutorial you will create a data file containg results drawn from Amdahl's Law by doing the following:

• In an open window type vi xmgr1.f to open a file in which you will create some Fortan code;
• In your vi window, type i to enter insert mode;
• Use the left mouse button to highlight the code displayed below:

program xmgr1 parameter(nmax = 100, v = 64.0) open(unit=2,file='test1_xmgr.dat',status='unknown') f = 0.0 do 1 n = 0,nmax s = 1.0/(1.0 - f + f/v) write(2,*)f,s f = f + .01 1 continue end

• Activate the vi window move the mouse there and left click if necessary) and then paste the bufferred text into the vi session by clicking the middle mouse button;
• Press Esc to exit insert mode and exit vi with :wq or ZZ to save the file xmgr1.f
• Compile your Fortran code with f77 xmgr1.f and execute it with a.out to produce the data file test1_xmgr.dat.

Having completed the above tasks, you now have a data file to load into the application xmgr. If xmgr is still running you can load the data file test1_xmgr.dat using the option File/Read sets.... This method will usually require that the viewport be rescaled to fit the data. This resizing can be accomplished by left clicking on the button marked on the left side of the xmgr window or with the option Graph/Autoscale.... If xmgr is not running then your data set can be loaded from the command line by typing xmgr test1_xmgr.dat . Loading from the command line will generally avoid the need to rescale the viewport.

HANDS ON 3 -- FORMATTING YOUR GRAPH

Before beginning this part of the tutorial, have a look at Figure 1 , which displays a bar graph of the the data set containing the results of program xmgr1.f. Your goal in this part of the tutorial is to create a graph that looks similar to that of Figure 1. Below, some of the steps required in formatting your graph are outlined to save you from having to search all of the menu items for the needed option.

• Load the data file test1_xmgr.dat using one of the options described above;
• Use the Graph/Graph operations.../Set graph type option to change the graph from the default cartesian xy format to bar graph format;
• Use Graph/Titles... to enter a title and subtitle similar to that of Figure 1;
• Use Graph/Tick labels/tick marks.. to label the horizontal and vertical axes;
• Use Graph/Frame... to flood the background with some color other than white (such as the blue in Figure 1);
• Use Graph/Symbols... to fill the bars in the bar graph and set the line color to the same as the fill color (red was used for both in Figure 1);
• Use the option Graph/Strings & things... to place an annotation within the frame;

At this point, your graph should look similar to that of Figure 1. If time permits continue your exploration of xmgr with the following:

• Reload the data file test1_xmgr.dat as an XY graph;
• Use Graph/Symbols... to display markers at the data points and change the thicknes and color of the graph curve;
• Use the Graph/Time stamp... option to date your work;

A single xmgr data file can contain multiple data sets. The following program illustrates the construction of such a data file with graphs separated by an ampersand (&). The three curves in the data file test2_xmgr.dat represent the solution to a diffusion PDE at different times. Physical interpretations of these curves could be the height of a groundwater mound or the temperature in a metal bar as a function of space at three different times.

EXAMPLE PROGRAM XMGR2

program xmgr2 parameter(nmax = 100, xmax = 10.) open(unit=2,file='test2_xmgr.dat',status='unknown') x = -xmax dx = 2.*xmax/float(nmax) t = 1.0 do 2 j = 1,3 do 1 n = 0,nmax y = .5*(erf((x+1)/sqrt(2.*t))-erf((x-1)/sqrt(2.*t))) write(2,*)x,y x = x + dx 1 continue write(2,*) '&' x = -xmax t = t + 1. 2 continue end

To gain more experience with xmgr, compile and execute the above program and repeat the formatting exercises of the previous hands-on exercises. Try some new commands under different headings.