xtlearn tutorial for Unix at CSE

Here are instructions for accessing and for basic use of xtlearn from CSE Unix workstations.

1. Log in on a pc.i86.linux machine (or start a remote shell on one):

   You may need to change directory to a location of your choice where you can create files (e.g. configuration, data and teach files for xtlearn.)

2. Copy the tutorial files to your chosen directory, by doing the Unix command:

   cp /home/cs9444/public/assigns/xtlearntute/xor.* .

   Don't forget that trailing full stop!

3. Run the command /home/cs9444/bin/xtlearn.
   This should bring up a rectangular xtlearn window.
   
   • From the File menu, choose Set Project.
   • Type xor into the text box and click OK.
   • Dismiss the warning box that says "Unable to open the project file".
   • Choose Network Architecture from the Displays menu.
   • Uncheck the Slabs check box. Slabs can be a better way to look at large and complex neural nets, but the xor net has only five neurons, so no slabs is better. Play with the other check boxes and the "Orient" radio buttons to see what they do.
   • Choose Training Options... from the Train menu.
   • This brings up a dialog window. Change the training sweeps from the default value to, say, 25000 sweeps. Change the learning rate from 0.1 (suitable for simple recurrent networks) to a less conservative 0.5. Click on the More... button to see some extra options, then eventually click OK.
   • Choose Error display from the Displays menu. You will see an (initially empty) graph of error against number of sweeps.
   • Choose Train the network from the Train menu. Watch the error display. Assuming that the error drops to a nice low value (less than about 0.05) you can probably assume that the network has learned successfully. You should probably choose Train the network a couple more times, to see some different error curves that correspond to different sets of random initial weights.
   • To test that the network has successfully learned, first choose Testing Options... from the Test menu. None of these options should need changing on this occasion, but if you wanted to use testing data that is different from the training data, you could click beside Novel data and type in the name of an alternative source of test data. Click OK.
   • Choose Verify network has learned from the Test menu. This will bring up a window labelled "xtlearn Testing Output" that lists the output values in the same order as the inputs appear in the .data file. In this case (xor) there is a single output unit, so you see a single column of numbers. The numbers will not be exactly 1 or 0, but should be close to one of these values. To see if they are (approximately) correct, you need to compare them to the numbers in xor.teach. cat this file (or view it in a text editor). The first two lines distributed and 4 tell you the data format and the number of training patterns. The remaining 4 lines are the ones you need to compare to the Testing Output values.
   • If the network does not seem to train correctly, go back to the Train menu and select Resume training. This will continue training the network for as many sweeps as you initially specified in the Training options... dialog window. Alternatively, e.g. if you want to train for lots more sweeps, you can go back to the Training options... dialog window, and change the Training sweeps to a large value.
   • To leave xtlearn, choose Quit from the File menu. :-)

4. You should now have some more files in your current working directory. As well as the three files that you started with: xor.cf, xor.data and xor.teach, you will have xor.prj, which is binary and so not fun to read, and various xor.nnn.wts, where nnn is a number. These give the weights at various stages when they were saved for you by xtlearn. They are readable. Their format is described in the tlearn reference manual.

5. What about the .err file that you will have to hand in with the simple recurrent nets assignment? Get back into xtlearn, open up xor as before, and then get into the Training options... dialog window. Check the "Log error every xxx sweeps" box, and type a number into the text (well, number) box. What number? How many numbers do you want? Maybe once every epoch is reasonable (but you may want to experiment - try once per sweep, once every 10 epochs, depending on how many epochs you train for). As there are 4 training patterns, once per epoch means logging error every 4 sweeps. Click OK, train the network, quit, and presto! you have an xor.err file. It's readable, and can easily get rather big ... Bear in mind that the assignment marker will not be amused if you hand in a megabyte of error log.

6. Use of the Connection weights display slows xtlearn down massively. Use with caution.

Good luck!