The homework this week was to implement a perceptron in Python.

Here is the code in Github and I copied it below. It was interesting to see/remember that the weighted sum of the inputs could be calculated with a dot product of the inputs vector with the weights vector.

I played a little with the learning rate and the number of tranining iterations, these I have worked well for the OR gate and for the AND gate.

import numpy as np # N = 2 # Number of inputs LearningRate = 0.1 # Learning rate # N += 1 # Increment 1 input because of the bias input # # Start with an array of random weights W = np.random.random( N )*2 - 1 print("Initial weights") print(W) # # This function calculates the weighted sum of inputs and return sign def infer(x): # The weighted sum is the dot product between inputs and weights s = np.dot(x,W) # Return the result of a function, in this case sign return np.sign(s) # # Receive an input / output pair and adjust the weights accordingly def train(x, y): print("Example") print(x) # Expected output for x expected = y print("Expected %d" % expected) # Get the output based in the current weights guessed = infer(x) print("Guessed: %d" % guessed) # Calculate the error error = expected - guessed print("Error: %f" % error) # The amount of change in the weights is proportional to the error and input deltaW = error*x print("DeltaW*LearningRate") # Multiply it by a constant (learning rate) and return the new weights print(deltaW*LearningRate) return W + deltaW*LearningRate # # Training data, truth table for OR # Input columns are first input, second input, and bias input (always 1) trainingX = np.array( [ [0,0,1], [0,1,1], [1,0,1], [1,1,1] ]) # Outputs are either -1 (False) or 1 (True) trainingY = np.array( [ -1, 1, 1, 1, ]) # # Train! # Repeat the training with the same data several times for i in range(10): print("Iteration number %d " % i) # For each example in the training data for index, x in enumerate(trainingX): print( "Training..." ) # Get the expected output y = trainingY[index] # Update the weights with the new ones W = train(x,y) # # Results print("Final weights") print(W) # # Infer! # Put the input data in the model and get the inferred results print("Starting inferences") for index,x in enumerate(trainingX): print("Input") print(x) print("Output") print(infer(x))

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