# Tag Info

6

Whenever you have a convex cost function you are allowed to initialize your weights to zeros. The cost function of logistic regression and linear regression have convex cost function if you use MSE for, also RSS, linear regression and cross-entropy for logistic regression. The main idea is that for convex cost function you'll have just a single optimal point ...

4

In particular, DQN is just Q-learning, which uses neural networks as a policy and use "hacks" like experience replay, target networks and reward clipping. In original paper authors use convolutional network, which takes your image pixels and then fit it into a set of convolutional layers. However there are a couple of statistical problems: DQN approximate ...

3

It's not actually possible to directly compare model coefficients. What you might do that would make more sense is to compare similar metrics. A good start would be to learn about explainability metrics that are comparable across models : LIME, SHAP... etc. (see here : https://christophm.github.io/interpretable-ml-book/) to see how models reacts on ...

3

Weights across different types of models are not always comparable, so I think that it would make more sense to do this kind of comparison not across different types of model but within a single type of model varying: the hyper-parameters (if any), the set of instances (e.g. selecting different subsets randomly), the set of features. I'd recommend in ...

2

Zeroing weights disables them. Yes, there are various applications of zero tensors (such as convex cost functions as you mention). Let's take the case of Neural Nets (NNs) and see if the math gives us more intuition: $$tensor\div0 = undefined\\ tensor * 0 = 0\\ tensor \cdot 0 = 0\\$$ Example Graph #1: How would one disable a single synapse connected to ...

2

In machine learning, the vanishing gradient problem is a difficulty found in training artificial neural networks with gradient-based learning methods and backpropagation. In such methods, each of the neural network's weights receives an update proportional to the partial derivative of the error function with respect to the current weight in each ...

2

One of the problems that can occur when training a neural network is known as the exploding gradient problem. A poorly initialised network could lead to a large increase in the norm of the gradient during training. These larger values will basically run the weights out of the number precision of the computer, resulting in NaN values. This post gives more ...

2

You need to specify the seed in the initializer, e.g: from keras.initializers import RandomUniform seed = 0 model.add(Dense(64, kernel_initializer = RandomUniform(minval = -0.05, maxval = 0.05, seed = seed)))

2

As per Efficient Backprop from Lecun (§4.6) weight should be initialized in the linear region of the activation function. If they are too big, activation function will saturate and provide small gradient step to change those weigth. If they are too small they won't really impact the gradient and make the learning too slow. Yes, if you choose the same weights ...

1

All the parameters are updated after a batch, there is no notion of order of update. The batch can or cannot be in the same order. It could lead to overfitting in the sense of the network learn the order of the dataset. An easy turnaround is to shuffle the batch between each epochs.

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It is fine if a hidden node has identical initial weights with nodes in a different layer, which is what I assume you mean by output weights. The problem with weight-symmetry arises when nodes within the same layer that are connected to the same inputs with the same activation function are initialized identically. To see this, the output of a node $i$ ...

1

One thing you can do is train your model N times and report the average and standard deviation of the accuracy. Is the train/test split fixed? That means, do you use the same train set for every evaluation? And do you have a stratified split? That means the class imbalance of your data is also present in the train and test data. Since your data is ...

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Basically, because the variance is quadratic in w. You can consider your problem as computing the variance over scalar products $z = \vec{x}\vec{w}$ by drawing 500000 samples of $\vec{w}$ from $p(\vec{w})$. Let's compute the mean first $$E_{p(\vec{w})} [ \vec{w}^T\vec{x} ] = \vec{\mu}_w^T \vec{x} = 0$$ because you draw the $\vec{w}$ from a zero-centered ...

1

Assuming that you normalized the pixel-values as it is done in the tutorial, your inputs were vectors of numbers betweeen 0 and 1. Now, if your weight matrices are also randomly drawn numbers between 0 and 1, the input to the hidden layer will be sums of 783 numbers between 0 and 1, i.e. probably something > 100. Now, check out the sigmoid function and its ...

1

I would venture that the problem you are having is at least due to bad initialisation, and it could also be a bad learning rate or activation functions. You mentioned that you are initializing conv kernels to "non zero unit matrices" and "fully connected layer weights as 0's". Firstly I do not know what you mean by "non zero unit matrices", but definitely ...

1

Three layers with one hidden layer? This sounds wrong. You have 2 layers, input -> hides -> output, that's only 2 layers, with two sets of weights. A single layer that gets initialized with only 0 will not converge, because the derivatives will be strictly identical (this rule also applies for any such last layer in a network, the layer gets basically ...

1

From what I understand, the difference between DQN and DDQN is in the calculation of the target Q-values of the next states. In DQN, we simply take the maximum of all the Q-values over all possible actions. This is likely to select over-estimated values, hence DDPG proposed to estimate the value of the chosen action instead. The chosen action is the one ...

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