python - multilayer perceptron, backpropagation, can´t learn XOR

Question

i am trying implement multilayer perceptron with backpropagation, but still i cant teach him XOR, i will also often get math range error. I looked in books and google for learning rules and error back propagation methods, but still i have no idea where are my mistakes

def logsig(net):
    return 1/(1+math.exp(-net))

def perceptron(coef = 0.5, iterations = 10000):
    inputs = [[0,0],[0,1],[1,0],[1,1]]
    desiredOuts = [0,1,1,0]
    bias = -1
    [input.append(bias) for input in inputs] 
    weights_h1 = [random.random() for e in range(len(inputs[0]))]
    weights_h2 = [random.random() for e in range(len(inputs[0]))]
    weights_out = [random.random() for e in range(3)]
    for itteration in range(iterations):
        out = [] 
        for input, desiredOut in zip(inputs, desiredOuts):
              #1st hiden neuron
            net_h1 = sum(x * w for x, w in zip(input, weights_h1)) 
            aktivation_h1 = logsig(net_h1)
              #2st hiden neuron
            net_h2 = sum(x * w for x, w in zip(input, weights_h2))
            aktivation_h2 = logsig(net_h2)
              #output neuron
            input_out = [aktivation_h1, aktivation_h2, bias]
            net_out = sum(x * w for x, w in zip(input_out, weights_out))
            aktivation_out = logsig(net_out)            
              #error propagation        
            error_out = (desiredOut - aktivation_out) * aktivation_out * (1-    aktivation_out)
            error_h1 = aktivation_h1 * (1-aktivation_h1) * weights_out[0] * error_out
            error_h2 = aktivation_h2 * (1-aktivation_h2) * weights_out[1] * error_out
              #learning            
            weights_out = [w + x * coef * error_out for w, x in zip(weights_out, input_out)]
            weights_h1 = [w + x * coef * error_out for w, x in zip(weights_h1, input)]
            weights_h2 = [w + x * coef * error_out for w, x in zip(weights_h2, input)]            
            out.append(aktivation_out) 
    formatedOutput = ["%.2f" % e for e in out]
    return formatedOutput

Answer 1

The only thing I notice is that you're updating weights_h1 and weights_h2 with error_out instead of error_h1 and error_h2. In other words:

weights_h1 = [w + x * coef * error_h1 for w, x in zip(weights_h1, input)]
weights_h2 = [w + x * coef * error_h2 for w, x in zip(weights_h2, input)] 

Answer 2

The math range error is likely coming from the math.exp(-net) calculation, for net a large negative number.