The Delta rule can be implemented using Excel. The User interface is not, perhaps, quite as nice as it could be made in Java or C++, but (given a working knowledge of Excel) you can see exactly what is going on.
I have produced a set of spreadsheets which learn the network which will compute the logical AND of two inputs. I have generated a number of spreadsheets, using differing output functions.
In the first three of these, 1 is TRUE and 0 is FALSE. In the fourth, -1 is used for FALSE. (There are sometimes problems making the Netscape Browser start up Excel from these links. Ideas? Try right-clicking...but this doesn't always work either). Try ftp, either from the browser (using ftp://ftp.cs.stir.ac.uk) or from a terminal window:
(then login as anonymous)
...and so on for the other files
Once you have the spreadsheet program, try altering the learning rate. What happens when it is very small? or when is is large? Can you suggest a mechanism for determining when it is too large?
It should also be a simple matter to alter it to make it learn different 2-input predicates, such as NOR, NAND and OR.
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email lss last updated 15 November 1999