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## Perceptron Learning Algorithm

The perceptron learning rule was originally developed by Frank Rosenblatt in the late 1950s.  Training patterns are presented to the network's inputs; the output is computed.  Then the connection weights wjare modified by an amount that is proportional to the product of
• the difference between the actual output, y,  and the desired output, d, and
• the input pattern, x.
The algorithm is as follows:
1. Initialize the weights and threshold to small random numbers.
2. Present a vector x to the neuron inputs and calculate the output.
3. Update the weights according to:
4.  where
• d is the desired output,
• t is the iteration number, and
• eta is the gain or step size, where 0.0 < n < 1.0

5. Repeat steps 2 and 3 until:
• the iteration error is less than a user-specified error threshold or
• a predetermined number of iterations have been completed.
Notice that learning only occurs when an error is made, otherwise the weights are left unchanged.

This rule is thus a modified form of Hebb learning.

During training, it is often useful to measure the performance of the network as it attempts to find the optimal weight set. A common error measure or cost function used is sum-squared error. It is computed over all of the input vector/output vector pairs in the training set and is given by the equation below:

where p is the number of input/output vector pairs in the training set.
[Back to the Simple Perceptron Learning applet page ]