# Questions tagged [kullback-leibler]

An asymmetric measure of distance (or dissimilarity) between probability distributions. It might be interpreted as the expected value of the log likelihood ratio under the alternative hypothesis.

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### KL divergence between two univariate Gaussians

I need to determine the KL-divergence between two Gaussians. I am comparing my results to these, but I can't reproduce their result. My result is obviously wrong, because the KL is not 0 for KL(p, p). ...
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### KL divergence between two multivariate Gaussians

I'm having trouble deriving the KL divergence formula assuming two multivariate normal distributions. I've done the univariate case fairly easily. However, it's been quite a while since I took math ...
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### Intuition on the Kullback-Leibler (KL) Divergence

I have learned about the intuition behind the KL Divergence as how much a model distribution function differs from the theoretical/true distribution of the data. The source I am reading goes on to say ...
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### Why do we use Kullback-Leibler divergence rather than cross entropy in the t-SNE objective function?

In my mind, KL divergence from sample distribution to true distribution is simply the difference between cross entropy and entropy. Why do we use cross entropy to be the cost function in many machine ...
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### Kullback–Leibler vs Kolmogorov-Smirnov distance

I can see that there are a lot of formal differences between Kullback–Leibler vs Kolmogorov-Smirnov distance measures. However, both are used to measure the distance between distributions. Is there a ...
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### Differences between Bhattacharyya distance and KL divergence

I'm looking for an intuitive explanation for the following questions: In statistics and information theory, what's the difference between Bhattacharyya distance and KL divergence, as measures of the ...
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### What is the advantages of Wasserstein metric compared to Kullback-Leibler divergence?

What is the practical difference between Wasserstein metric and Kullback-Leibler divergence? Wasserstein metric is also referred to as Earth mover's distance. From Wikipedia: Wasserstein (or ...
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### Measures of similarity or distance between two covariance matrices

Are there any measures of similarity or distance between two symmetric covariance matrices (both having the same dimensions)? I am thinking here of analogues to KL divergence of two probability ...
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### An adaptation of the Kullback-Leibler distance?

Look at this picture: If we draw a sample from the red density then some values are expected to be less than 0.25 whereas it is impossible to generate such a sample from the blue distribution. As a ...
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### Why KL divergence is non-negative?

Why is KL divergence non-negative? From the perspective of information theory, I have such an intuitive understanding: Say there are two ensembles $A$ and $B$ which are composed of the same set of ...
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### What is the relationship between the GINI score and the log-likelihood ratio

I am studying classification and regression trees, and one of the measures for the split location is the GINI score. Now I am used to determining best split location when the log of the likelihood ...
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### Analysis of Kullback-Leibler divergence

Let us consider the following two probability distributions ...
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### Kullback-Leibler divergence - interpretation [duplicate]

I have a question about the Kullback-Leibler divergence. Can someone explain why the "distance" between the blue density and the "red" density is smaller than the distance between the "green" curve ...
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### Deriving the KL divergence loss for VAEs

In a VAE, the encoder learns to output two vectors: $$\mathbf{\mu} \in\ \mathbb{R}^{z}$$ $$\mathbf{\sigma} \in\ \mathbb{R}^{z}$$ which are the mean and variances for the latent vector $\mathbf{z}$, ...
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### What's the maximum value of Kullback-Leibler (KL) divergence

I am going to use KL divergence in my python code and I got this tutorial. On that tutorial, to implement KL divergence is quite simple. ...
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### How to compute the Kullback-Leibler divergence when the PMF contains 0s?

I have the following timeseries obtained using the data posted below. For a sliding window size of 10, I am trying to compute the KL-divergence between the PMF of values within the current sliding ...
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### Why is Kullback-Leilbler divergence a better metric for measuring distance between two probability distributions than squared error? [duplicate]

I know that KL-divergence is a metric that is more suitable when we want to measure the distance between numbers which a probability form. However, I am still confused what is the benefit of using KL-...
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### KL divergence and expectations

I am trying to understand the explanation of the KL divergence per below. It refers, as i understand it, to an expectation in the second term. "Approximating the expectation over q in this term". ...
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### Why KL-Divergence uses “ln” in its formula?

I notice in KL-Divergence formula a $ln$ function is used: $${D_{KL}}(P||Q) = \sum\limits_i {P(i)} \ln \frac{{P(i)}}{{Q(i)}},$$ where $i$ is a point and $P(i)$ the true discrete probability ...
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### Why does the Bayesian posterior concentrate around the minimiser of KL divergence?

Consider the Bayesian posterior $\theta\mid X$. Asymptotically, its maximum occurs at the MLE estimate $\hat \theta$, which just maximizes the likelihood $\operatorname{argmin}_\theta\, f_\theta(X)$. ...
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### Population stability index - division by zero

Population stability index quantifies the change of a distribution of a variable by comparing data samples in two time periods. It is very commonly used to measure shifts in scores. It is calculated ...
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### Kullback-Leibler divergence: negative values? [duplicate]

Wikipedia - KL properties says that KL can never be negative. But e.g. for texts where the probabilities are very small I somehow get negative values? E.g. Collection A: - word count: 321 doc count:...
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### Why is there a E in the name EM algorithm?

I understand where the E step happens in the algorithm (as explicated in the math section below). In my mind, the key ingenuity of the algorithm is the use of the Jensen's inequality to create a lower ...
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### What is the KL divergence of distribution from Dirac delta?

The Kullback–Leibler (KL) divergence of two continuous distributions $P(x)$ and $Q(x)$ is defined as $$D_{KL}(P \mid\mid Q) = \int_{X} P(x) \log{\left[\frac{P(x)}{Q(x)}\right]} dx$$ How can one ...
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### How should I intuitively understand the KL divergence loss in variational autoencoders? [duplicate]

I was studying VAEs and came across the loss function that consists of the KL divergence. $$\sum_{i=1}^n \sigma^2_i + \mu_i^2 - \log(\sigma_i) - 1$$ I wanted to intuitively make sense of the KL ...
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### G-test statistic and KL divergence

According to Wikipedia, the G-test statistic is "proportional to the Kullback–Leibler divergence of the empirical distribution from the theoretical distribution." To get the relationship between $G$ ...
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### Multivariate time series model evaluation with conditional moments

Consider multivariate time series models that estimate potentially time-varying conditional means, variances, and correlations (one type of model might be a VAR(p)+Garch(1,1)+DCC Gaussian Copula model)...
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### Use of KL Divergence in practice

It's not symmetric, so it can't really be used as a distance metric. I suppose given two known distributions p(x) and q(x), if one found another distribution z(x) but knew it came from either p or q,...
Suppose we seek to approximate an arbitrary distribution $p_1(x)$ by a normal $p_2(x) \sim \mathcal N(\mu, \Sigma)$. How can I show that the values that lead to the smallest Kullback–Leibler ...
Machine learning classifiers often use the cross-entropy $\mathbb{H}[p,q]$, where $p$ is the true distribution (often a delta) and $q$ is the predicted distribution over classes (or can at least be ...