Neural Networks: Building with Tensorflow for XOR

The learning algorithm is a principled way of changing the weights and biases based on the loss function. From there, we perform the forward propagation by looping over all layers in our network on Line 140. We start looping over every layer in the network on Line 71. The net input to the current layer is computed by taking the dot product between the activation and the weight matrix (Line 76).

The sample code from this post can be found here.

These sigmoid functions are very similar, and the output differences are small. Note that all functions are normalized in such xor neural network a way that their slope at the origin is 1. On Line 131, we initialize p, the output predictions as the input data points X.

  1. Is there some kind of regularization happening on the parameters that force them to stay close to 0?
  2. The fit method requires two parameters, followed by two optional ones.
  3. One of the main problems historically with neural networks were that the gradients became too small too quickly as the network grew.
  4. Further, this error is divided by 2, to make it easier to differentiate, as we’ll see in the following steps.
  5. The sigmoid is a smooth function so there is no discontinuous boundary, rather we plot the transition from True into False.

Deep learning neural networks are trained using the stochastic gradient descent optimization algorithm. As part of the…

I am a total noob and this is first thing in ML im trying to do. I just want to run the code.I know feedforward is correct and my errors should be correct, but I get incorrect results. But what logic did the model use to solve the XOR problem?


For better understanding, let us assume that all our input values are in the 2-dimensional domain. Observe the expression below, where we have a vector \(x\) that contains two elements, \(x_1\) and \(x_2\) respectively. Is there a magic sequence of parameters to allow the model to infer correctly from the data it hasn’t seen before?

Neural Network for XOR approximation always outputs 0.5 for all inputs

Notice how we are importing our newly implemented NeuralNetwork class. On Line 14, we start looping over the number of layers in the network (i.e., len(layers)), but we stop before the final two layer (we’ll find out exactly why later in the explanation of this constructor). Line 8 initializes our list of weights for each layer, W.

A perceptron can only converge on linearly separable data. Therefore, it isn’t capable of imitating the XOR function. If not, we reset our counter, update our weights and continue the algorithm. We know that a datapoint’s evaluation is expressed by the relation wX + b . This is often simplified and written as a dot- product of the weight and input vectors plus the bias. The perceptron basically works as a threshold function — non-negative outputs are put into one class while negative ones are put into the other class.

Keep in mind that during the backpropagation step we looped over our layers in reverse order. To perform our weight update phase, we’ll simply reverse the ordering of entries in D so we can loop over each layer sequentially from 0 to N, the total number of layers in the network (Line 115). We then initialize a list, A, on Line 67 — this list is responsible for storing the output activations for each layer as our data point x forward propagates through the network. We initialize this list with x, which is simply the input data point. Looking at the node values of the hidden layers (Figure 2, middle), we can see the nodes have been updated to reflect our computation.

The best performing models are obtained through trial and error. To train our perceptron, we must ensure that we correctly classify all of our train data. Note that this is different from how you would train a neural network, where you wouldn’t try and correctly classify your entire training data. That would lead to something called overfitting in most cases.

Since, there may be many weights contributing to this error, we take the partial derivative, to find the minimum error, with respect to each weight at a time. Now let’s build the simplest neural network with three neurons to solve the XOR problem and train it using gradient descent. Remember the linear activation function we used on the output node of our perceptron model? You may have heard of the sigmoid and the tanh functions, which are some of the most popular non-linear activation functions. We now have a neural network (albeit a lousey one!) that can be used to make a prediction. To make a prediction we must cross multiply all the weights with the inputs of each respective layer, summing the result and adding bias to the sum.

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