Questions tagged [notation]

For questions related to notation (in general).

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What are the steps to derive the original GAN loss function from the generalized version?

I am trying to understand how the loss function from the original GAN paper $$\min_{G} \max_{D} V(D, G)=\mathbb{E}_{\boldsymbol{x} \sim p_{\text {data }}(\boldsymbol{x})}[\log D(\boldsymbol{x})]+\...
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Does $R_{s}=E[R_{t}|S_{t}=s]$ indicate the reward we might expect on getting on average moving from any other state to $s$?

I'm trying to understand correctly what each "variable" in RL is and I'm not sure about $R_{s}$ the reward function. I used to think that it's the reward we may expect on average after ...
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Why $ t=τ+n-1$ instead of $t=τ+n$ in n-step TD?

If $\tau$ is the time, whose state’s estimate is being updated, and $t$ is the current time, then, in n-step TD method, we have $t=\tau+n$ (because we have to wait n-steps, before we can update). ...
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Why do we have $t$ as subscript in $V$ instead of $t+1$ in the expression of $G_{t:t+1}$?

In one-step TD updates, the target is the first reward plus the discounted estimated value of the next state, which we call the one-step return (page 143 of Sutton & Barto): $$ G_{t:t+1} \...
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What do the square brackets $[ ]$ and $\mid$ mean in $[G_t \mid S_t=s]$?

Here is the formula of state-value function in Reinforcement Learning. What do the square brackets $[ ]$ and $\mid$ mean in $[G_t \mid S_t=s]$? Why use square brackets? Why use $\mid$? Why do ...
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Where are the parentheses in the Bellman update rule?

I'm not having a lot of intuition about the equation. I have this Bellman update rule: $$v_{\pi}(s) =\sum_a \pi(a|s)\sum_{s',r} p(s',r|s,a)[r+ \gamma v_{k}(s')]$$ But where are the parenthesis? Is the ...
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What does the complexity equation constitute exactly in “Why Should I Trust You?” LIME paper

I've recently been reading this paper on LIME, an algorithm to interpret ANY machine learning model. I encountered this equation (in red) on page 4 and have just been having a hard time deciphering ...
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Why do we use $q_{\phi}(z \mid x^{(i)})$ in the objective function of amortized variational inference, while sometimes we use $q(z)$?

In page 21 here, it states: General Idea of Amortization: if same inference problem needs to be solved many times, can we parameterize a neural network to solve it? Our case: for all $x^{(i)}$ we ...
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Are the authors of the VAE paper writing the PDFs as a function of the random variables?

Usually, I see the conventions: discrete random variable is denoted as $X$, the pmf is written as $P(X=x)$ or $p(X=x)$ or $p_{X}(x)$ or $p(x)$, where $x$ is an instance of $X$ a continuous random ...
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Which is more popular/common way of representing a gradient in AI community: as a row or column vector?

Consider the following remark about writing gradients from the chapter named Vector Calculus from the test book titled Mathematics for Machine Learning by Marc Peter Deisenroth et al. Remark (...
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What is the name of this letter $\mathcal{J}$?

What is the name of this letter $\mathcal{J}$ in the following deep learning equation? And what alphabet it is from? $$\mathcal{J} = \frac{1}{m} \sum_{i=1}^m \mathcal{L}^{(i)}$$
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What is a filter in the context of graph convolutional networks?

In Section 2.1 of the research paper titled Semi-Supervised Classification with Graph Convolutional Networks by Thomas N. Kipf et al., Spectral convolution on graphs defined as The multiplication of ...
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In this example of fuzzy c-means, what is the difference between "sigma" and "center" for the clusters?

In this example, what exactly do "Cluster" and "Sigma" mean? (They chose random coordinates for the three centroids of the groups) Centers: Cluster centers, returned as a ...
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Why using negative integers (as dimensions?) in tensor shapes rather than natural numbers?

Consider the following paragraph from A.1 MULTI-MNIST AND CLEVR of A IMPLEMENTATION DETAILS from the research paper titled ...
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What, exactly, do mlp(64,64) and mlp(64,128,1024) mean in PointNet, and how many input neurons does 1 (x,y,z) point have?

I couldn't find out how to interpret the multilayer perceptron notation given in PointNet. Specifically, I am looking to find out what the numbers inside the parentheses of ...
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Is there any difference between input and conditional input incase of neural networks?

In the research paper titled Conditional Generative Adversarial Nets by Mehdi Mirza and Simon Osindero, there is a notion of conditioning a neural network on class label. It has been mentioned in <...
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Does generator in conditonal GAN obey probability laws?

In probability, we have two types of probability functions: unconditional probability $p(x)$ and conditional probability $p(x | y)$. Both are fundamentally different and the latter can be obtained by ...
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1 vote
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Is it abuse of notation to use tilde operator in this context?

The following is a way to use tilde (∼) in context of random variables or random vectors. In statistics, the tilde is frequently used to mean "has the distribution (of)," for instance, $X∼N(...
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-1 votes
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Why is noise vector represented by letter $z$? [closed]

Most of the notations in Artificial Intelligence are borrowed from the mathematics. $x$ stands for input (vector), $y$ stands for output (vector) etc., and the list is long. But, I am not sure whether ...
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3 votes
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Is the Bandit Problem an MDP?

I've read Sutton and Barto's introductory RL book. They define a policy as a mapping from states to probabilities of selecting each possible action. If the agent is following policy $\pi$ at time $t$, ...
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To denote a training example should I use row vector or column vector?

This code accesses the first 3 examples in the iris data set, from sklearn.datasets import load_iris iris = load_iris() print(iris.data[:3]) and gives ...
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What is the correct notation for an operation that applies to each element of an array independently?

I am looking for the standard notation to define element-wise / Hadamard-style functions, if there is one. That is to say, if the operator I am looking for were represented by a hexagon ⬡, I could use ...
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1 vote
2 answers
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In variational autoencoders, what does p(x|z) mean?

If $x \sim \mathcal{N}(\mu,\,\sigma^{2})$, then it is a continuous variable, and therefore $P(x) = 0$ for any x. One can only consider things like $P(x<X)$ to get a probability greater than 0. So ...
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Does a trajectory in reinforcement learning contain the last action?

From what I learn from CS285 and OpenAI's spinning up, a trajectory in RL is a sequence of state-action pairs: $$\tau = \{s_0, a_0, ..., s_t, a_t\}$$ And the resulting trajectory probability is: $$ P(\...
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1 vote
1 answer
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Why is the behaviour policy denoted by $\beta$ and the exploration policy by $ \mu'$ in the DDPG paper?

I am learning about the deep deterministic policy gradient (DDPG) (Lillicrap et al, 2016) and got confused about the notation of the behavior policy. Lillicrap et al. denote the policy gradient by $$\...
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2 votes
1 answer
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What do the variables in the cross-correlation formula mean?

I understand what cross-correlation does given a kernel and an input image, but the formula confuses me a little. Given here in Goodfellow's Deep Learning (page 329), I can't quite understand what $m$ ...
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2 votes
1 answer
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What is $ \nabla_{\theta_{k-1}} \theta_{k}$ in the context of MAML?

I am attempting to fully understand the explicit derivation and computation of the Hessian and how it is used in MAML. I came across this blog: https://lilianweng.github.io/lil-log/2018/11/30/meta-...
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3 votes
2 answers
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What does the parameter $y$ stand for in function $g(y,\mu,\sigma)$ related to REINFORCE algorithm?

I am wondering what the parameter $y$ in the function $g(y,\mu,\sigma)=\frac{1}{(2\pi)^{1/2}\sigma}e^{-(y-\mu)^{2/2\sigma^2}}$ stands for in Section 6 (page 14) of the paper introducing the REINFORCE ...
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2 votes
1 answer
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In AlphaZero, do we need to store the data of terminal states?

I have a question about the training data used during the update/back-propagation step of the neural network in AlphaZero. From the paper: The data for each time-step $t$ is stored as ($s_t, \pi_t, ...
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1 answer
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What is the meaning of these equations in Noise2Noise paper?

I am trying to understand what is meant by following equations in the Noise2Noise paper by Nvidia. What is meant by the equation in this image? What is $\mathbb{E}_y\{y\}$? And how should I try to ...
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1 vote
1 answer
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In the definition of the state-action value function, what is the random variable we take the expectation of?

I know that $$\mathbb{E}[g(X) \mid A] = \sum\limits_{x} g(x) p_{X \mid A}(x)$$ for any random variable $X$. Now, consider the following expression. $$\mathbb{E}_{\pi} \left[ \sum \limits_{k=0}^{\infty}...
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Do the rows of the design matrix refer to the observations or predictors?

I attempt to understand the formulation of dictionary learning for this paper: Depression Detection via Harvesting Social Media: A Multimodal Dictionary Learning Solution Multimodal Task-Driven ...
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3 votes
1 answer
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What does the notation $\mathcal{N}(z; \mu, \sigma)$ stand for in statistics?

I know that the notation $\mathcal{N}(\mu, \sigma)$ stands for a normal distribution. But I'm reading the book "An Introduction to Variational Autoencoders" and in it, there is this notation:...
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4 votes
2 answers
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Why do we use $X_{I_t,t}$ and $v_{I_t}$ to denote the reward received and the at time step $t$ and the distribution of the chosen arm $I_t$?

I'm doing some introductory research on classical (stochastic) MABs. However, I'm a little confused about the common notation (e.g. in the popular paper of Auer (2002) or Bubeck and Cesa-Bianchi (2012)...
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4 votes
1 answer
113 views

What does the term $|\mathcal{A}(s)|$ mean in the $\epsilon$-greedy policy?

I've been looking online for a while for a source that explains these computations but I can't find anywhere what does the $|A(s)|$ mean. I guess $A$ is the action set but I'm not sure about that ...
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0 votes
1 answer
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What does the notation "for t=T to 1,−1 do" in terms of time steps, in deep recurrent q network?

In looking at an algorithm in the paper Learning to Communicate with Deep Multi-Agent Reinforcement Learning. Here is the full algorithm: What does the notation ...
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1 vote
1 answer
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What do the notations $\sim$ and $\Delta (A) $ mean in the paper "Fairness Through Awareness"?

In this paper Fairness Through Awareness, the notation $\mathbb{E}_{x \sim V} \mathbb{E}_{a \sim \mu_x} L(x,a)$ is being used (page 5 top line), where $V$ denotes the set of individuals (so I guess ...
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4 votes
2 answers
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Why are the value functions sometimes written with capital letters and other times with lower-case letters?

Why are the state-value and action-value functions are sometimes written in small letters and other times in capitals? For instance, why in the Q-learning algorithm (page 131 of Barto and Sutton's ...
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1 vote
1 answer
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What does the notation $\partial \theta_{\pi}$ mean in this actor-critic update rule?

One of the steps in the actor-critic algorithm is $$\partial \theta_{\pi} \gets \partial \theta_{\pi} + \nabla_{\theta}\log\pi_{\theta} (a_i | s_i) (R - V_{\theta}(s_i))$$ For me, $\theta$ are just ...
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1 vote
1 answer
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What does equation in the "related work" section of the GAN paper mean?

I was going through the paper on GAN by Ian Goodfellow. Under the related work section, there is an equation. I cannot decipher the equation. Can anyone help me understand the meaning of the equation? ...
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2 votes
1 answer
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What does the notation ${s'\sim T(s,a,\cdot)}$ mean?

I have been seeing notations on Expectations with their respective subscripts such as $E_{s_0 \sim D}[V^\pi (s_0)] = \Sigma_{t=0}^\infty[\gamma^t\phi(s_t)]$. This equation is taken from https://ai....
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  • 1,201
2 votes
0 answers
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How is the gradient with respect to weights derived in batch normalization?

At the bottom of page 2 of the paper L2 Regularization versus Batch and Weight Normalization, the equation for the gradient of the output with respect to the weights is given as: $$ \triangledown y_{...
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1 vote
1 answer
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What is the purpose of the arrow $\leftarrow$ in this formula?

What is the purpose of the arrow $\leftarrow$ in the formula below? $$V(S_t) \leftarrow V(S_t) + \alpha \left[ G_t - V(S_t) \right]$$ I presume it's not the same as 'equals'.
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Why is exp used in encoder of VAE instead of using the value of standard deviation alone?

There's one VAE example here: https://towardsdatascience.com/teaching-a-variational-autoencoder-vae-to-draw-mnist-characters-978675c95776. And the source code of encoder can be found at the ...
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How to understand the average l2 loss?

In the snippet below, the highlighted part is the average norm, but since $1/|p_i|$ is outside the summation, it is very confusing to understand. is $|p_i|$ l2-norm(as per wolfram) or l1-norm or ...
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3 votes
1 answer
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What is the difference between the notations $\|x\|_1, \|x\|_2$ and $|x|$?

What is the difference between the notations $\|x\|_1, \|x\|_2$ and $|x|$? I think $|x|$ is the magnitude of $x$.
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3 votes
1 answer
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What does the notation sup dist mean in distributional RL?

I'm trying to understand distributional RL, based on this article. In one of the equations, there is a symbol $\operatorname{sup dist}$. \begin{align} \operatorname{sup dist}_{s, a} (R(s, a) + \...
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3 votes
2 answers
877 views

What is a probability distribution in machine learning?

If we were learning or working in the machine learning field, then we frequently come across the term "probability distribution". I know what probability, conditional probability, and ...
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4 votes
1 answer
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What do the subscripts mean in $N_{t,n,\sigma,L}$?

A neural network can apparently be denoted as $N_{t,n,\sigma,L}$. What do these subscripts $t, n, \sigma$ and $L$ mean? Could you link me to a paper, article or webpage with an explanation for this?
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3 votes
1 answer
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Sutton & Barto's notation $V_{t+n}$ in Chapter 7: $n$-step Bootstrapping

Until Chapter 6 of Sutton & Barto's book on Reinforcement Learning, the authors use $V$ for the current estimate of a state value. Equation (6.1), for example, shows: $$ V(S_t) \leftarrow V(S_t) +...
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