Questions tagged [wishart-distribution]
The Wishart distribution is a common matrix distribution on square symmetric semi-definite matrices.
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From GMM to Wishart MM
Given a random vector $X$ distributed as a vector Gaussian mixture model in $\mathbb R^n$ mixing $K$ centered multivariate Gaussian distributions as follows
$$
\textstyle X \sim \sum_{i=k}^K \alpha_k \...
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Partition of a Multivariate Normal Distribution with Inverse-Wishart Covariance Prior
I'm trying to partition a multivariate normal with the following structure:
$$\bf{X} = \left. \begin{bmatrix} \bf{X}_1 \\ \bf{X}_2 \end{bmatrix}\right|\Sigma \sim N_p \left(\begin{bmatrix} \mu_1 \\ \...
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What is the expectation of the Cholesky factor of a Wishart distributed random matrix?
Let a $d-\text{dimensional}$ Wishart random variable with $\nu$ degrees of freedom $\Sigma$ be distributed according to $\mathcal{W}(\Sigma|\Sigma_0, \nu) \propto |\Sigma|^\frac{\nu-d-1}2\exp{(-\...
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On the Wishart distribution
Definitions
Consider the following bivariate model
\begin{equation*}y\triangleq S(p)h+v\end{equation*}
where
$p\triangleq \begin{bmatrix}\theta & \ell_1 & \ell_2\end{bmatrix}'$ and $\theta \...
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Clustering with gaussian mixtures: choice of hyperparameters
Question: I am interest in general in understanding how to choose the hyperparameters if we are interested in clustering bivariate vectors assuming a mixture of Gaussian mixture with conjugate Normal-...
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Is there a closed form solution for the Hellinger Distance between two Wishart distributions?
Given two Wishart distributions $X_0 \sim W_{p_0}(V_0,n_0)$, $X_1 \sim W_{p_1}(V_1,n_1)$, what is the Hellinger Distance between them? Can it be obtained in closed form assuming $p_0 = p_1$?
For ...
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Marginal likelihood of bivariate Gaussian model
I assume the following model for a sample $y_1 \in \mathbb{R}^2$ of size $1$ with bivariate Gaussian likelihood and independent bivariate Gaussian and inverse-Wishart prior for the mean and variance ...
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Variance of $\operatorname{tr}(W^2)$ with $W \sim \text{Wishart}(n, \Sigma)$
Suppose $W \sim \text{Wishart}(n, \Sigma)$, where $\Sigma \in \mathbb R^{p\times p}$, the expectation of $\operatorname{tr}(W^2)$ is
$$E[\operatorname{tr}(W^2)] =n(n+1)\operatorname{tr}(\Sigma^2) + n\...
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Finite integral vs Finite probability Density
I was reading the Bayesian Data Analysis book from Gelman et al. I was going through Appendix A which describes probability distributions, and realize the book talks about something I don't really ...
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How to impose restrictions on a random matrix via its prior distribution?
I am reading the paper Factor analysis and outliers: A Bayesian approach. The author starts with a factor analysis model given by
$${\bf y}_i = {\bf \Lambda} {\bf z}_i + {\bf e}_i, \quad i = 1, \ldots,...
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Kullback–Leibler divergence between two inverse Wishart distributions
Is there a closed form formula for the KL divergence between two inverse Wishart distributions?
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Marginal distribution for the off-diagonal elements of a Matrix following an Inverse-Wishart
I've found on CV the marginal distribution for the main-diagonal elements of a matrix which follows an Inverse-Wishart distribution.
However, what will happen to the off-diagonal elements? what ...
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How to Estimate Covariance Matrix using Wishart Distribution?
I learned that Wishart distribution can help estimate covariance matrix of MVN without sampling directly from MVN. But there are some points that are still unclear for me:
Why we bother to estimate ...
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How to calculate the Jacobian of the transformation ( for covariance matrix)
I'm reading this Paper about a separation strategy for modeling covariance matrices with focus on Bayesian analysis. Direct decomposition of covariance matrix is as follows: $\Sigma = \text{diag}(S)\,...
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Kullback Leibler Divergence between two Normal Whishart Distributions
I'm having trouble to compute the KL Divergence between two normal-Wishart distributions. KL divergence from $Q$ to $P$ is defined as:
$$D_{\mathrm{KL}}(P \Vert Q) = \int p(x) \log \frac{p(x)}{q(x)}...
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Sum of Log Chi-Squared Asymptotic Distribution
I'd like to find the asymptotic distribution of
$$\sqrt{n}\left(\log|\mathbf{S}| - \log|\boldsymbol{\Sigma}|\right), ~~~~~n \rightarrow \infty$$
where $\mathbf{S} \sim W_j\left(n, \frac{\boldsymbol{\...
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Sampling prior covariance matrices - nested sampling
I am trying to fit a multivariate Gaussian with a non-diagonal covariance matrix $\Sigma$ using nested sampling.
Usually, in other Bayesian analyses, we would use a Inverse Wishart or LKJ prior on ...
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Semi-conjugate inverse Wishart posterior, can we obtain the marginal?
In Hoff's text (A First Course in Bayesian Statistical Methods), he uses a semi-conjugate inverse-Wishart prior for the covariance matrix of a multivariate normal process. In equation 7.9, he has the ...
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Showing a useful result for Wisharts and Multivariate Beta random matrices
Let $\mathbf{A} \sim \text{Wishart}_m\left(k_a,\mathbf{V} \right)$ and $\mathbf{B} \sim \text{Wishart}_m\left(k_b,\mathbf{V} \right)$ be two full rank Wishart random matrices. Define
$$
\mathbf{S} = \...
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Inverse Wishart Prior for linear model
I know some bayesian methods employ an inverse wishart distribution for the prior distribution of the covariance matrix in a linear regression. I.e. for the model:
$$Y=X\beta+\epsilon$$
Where $\...
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Estimate parameters of inv-Wishart distribution using Bayesian
$\Sigma \sim Inv-Wishart_{v}(\Lambda^{-1})$
Suppose that I have a set of observations of $\Sigma$s, I wonder if there is a conjugate way to estimate the value of $v$ and $\Lambda$ (especially $\...
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Integrate out (covariance) matrix in Normal-Wishart distribution
In Gelman's Bayesian Data Analysis Chapter 3.6, he introduces the multivariate normal with unknown mean and variance, with the priors
$\Sigma\sim \text{Inv-Wishart}_{\nu_0}(\Lambda_0^{-1})$
$\mu\...
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Is assigning an inverse-Wishart distribution to a diagonal matrix problematic?
I'm reading the paper Bayesian Vector Autoregressions by Thomas Wozniak. He considers the model
$$y_t = \mu + A_1 y_{t-1} + \cdots A_k y_{t-k} + u_t$$ where each $y_i$ is a $N$-vector, each $A_j$ is a ...
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Integrating the inverse-Wishart density
It is alleged in this question and in the Wikipedia article and elsewhere that the density function for the inverse-Wishart distribution with $n$ degrees of freedom on $p\times p$ positive-definite ...
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What's the role of the scale matrix for the Inverse-Wishart and Wishart distributions?
What's the role of the scale matrix for the Inverse-Wishart and Wishart distributions?
The purpose of finding this information is to enlighten me on how should one decide on a prior for a positive-...
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Deriving the sampling distribution of MLE for Normal distribution
Let $X_1,\ldots,X_n$ be an observed random sample from $N_p(\mu, \Sigma)$.
I know that the MLE of $\Sigma$ is $\frac{1}{n} \sum_i^n(X_i -\bar X)(X_i -\bar X)^T$, which is biased.
We define $S = \...
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Marginal Distribution of Matrix Normal with Two Inverse Wisharts
Say I have a Matrix-Normal distribution and two Inverse Wishart Distributions
$$X \sim MN_{p\times n}(0, \Sigma, \Omega)$$
$$ \Sigma \sim IW(a, A) $$
$$ \Omega \sim IW(b, B)$$
where $a$ and $b$ are ...
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Appropriate Distribution for Diagonal Covariance Matrices
Let's say I have a model like:
\begin{align}
X\mid\mu,\Sigma_X &\sim \mathcal{N}(\mu,\Sigma_X)\\
\mu\mid m, \Sigma_\mu &\sim \mathcal{N}(m,\Sigma_\mu) \\
\Sigma_X\mid \Psi, c &\sim \...
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Intuitive explanation of Inverse Wishart prior for covariance estimation
I am trying to understand what is going on in the use of an Inverse Wishart prior for (Gaussian) covariance, and what is the motivation for it. I am seeing this posed as a solution for when the ...
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How do I find the "elliptical confidence region" from columns of a matrix that follows the Wishart distribution?
The subject is about the sample mean and the sample covariance estimators and their respective confidence regions for the estimated parameters.
Suppose that $n$ samples are taken from a $p$-variate ...
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Transformation of Inverse Wishart
Let $\Sigma$ be an $p\times p$ dimensional covariance matrix that is distributed Inverse Wishart with degrees of freedom $\nu$ and Prior scale matrix $\Psi$ such that we write $\Sigma \sim W^{-1}(\nu, ...
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Expected eigenvalues of a Wishart Matrix
I consider a $n\times n$ Wishart Matrix with expected value $p \cdot I_n$, i.e. a matrix of the form
$$W = XX'$$
with $X$ a $n\times p$ matrix with independent standard normal entries.
It is easy ...
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What is the relationship between the normalization constants of the normal distribution and the (Inverse-)Wishart distribution?
I was looking at the probability density function of the multivariate normal distribution and that of the inverse-Wishart distribution:
$$
\begin{array}{rccll}
p_{\mathcal{N}}\left(\mathbf{x}; \...
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Scaling for Wishart distribution
If $X$ has a Wishart distribution $W_p(n,\Sigma)$ , what's the distribution for $cX$ where $c>0$ ?
I know that for a $\chi^2_n (x)$ distribution with $n$ degrees of freedom, $c\chi^2 $ follows $\...
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Expectation of the inverse of $\textbf{z} \textbf{z}^{H}$ where $\textbf{z}$ is a complex Gaussian vector
Considering the vector $\textbf{z} \sim \mathcal{CN}(\textbf{0}_{M},\Theta_{M \times M})$, what would be the expectation of $\frac{1}{\textbf{z} \textbf{z}^{H}}$, i.e.,
$\mathbb{E} \left\lbrace \frac{...
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Property of Wishart distribution
I am solving the next exercise about a property of a Wishart Distribution:
$$M_1\sim W_p(\Sigma,n_1)$$
$$M_2\sim W_p(\Sigma,n_2)$$
are independent, then $M_1+M_2\sim W_p(\Sigma,n_1+n_2)$
I have ...
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Result for covariance between elements of the sample covariance matrix
Given data matrix $X_{n,p}$ where $n$ is the sample size, $p$ is the dimension, the sample covariance is
$$\hat{\Sigma}=\frac{1}{n-1}X^\top X=\{\hat{\sigma}_{ij}\}_{1\le i,j\le p}$$
Is there any ...
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Maximum Likelihood of Wishart parameters
I'm having some difficulty in deriving the ML estimation of the parameters of a Wishart distribution.
Given a set of matrices $\{W_1, W_2,\dots,W_N\} \in \mathbb{C}^{k\times k}$ for which $W_i \sim ...
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Is Wishart distance always positive?
From what is told on page 268 of the Polarimetric Radar Imaging: From Basics To Applications:
I have written the following code for wishart distance calculation in Matlab:
...
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expectation associated with Wishart distribution
Suppose that $W$ follows the Wishart distribution with parameter $\Sigma$ and d.f. $n$.
Then, I would like to know the result of the following expectations.
$E[tr(WAWB)tr(WC)]$
$E[tr(WAWB)tr(WCWD)]$...
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Unsolvable Integral?
Is the following integral solvable?
$$P(X) = \int^{\infty}_{-\infty} \int^{\infty}_{-\infty} P(X|\mu,K)P(\mu|K)P(K) d\mu dK$$
with
$$P(K) = \frac{|K| ^{(v-d-1)/2}}{2^{vd/2}|V|^{v/2}\Gamma_d|\frac{...
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use inverse Wishart for variance in MCMC
When you have a posterior that looks like as one step in Gibber Sampler
$P(\xi | \Sigma_\xi, \theta) ∝ exp\{-1/2 \xi\Sigma_\xi^{-1}\xi\}P(data | \xi, \theta)$
Do you always assume inverse Wishart ...
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Distribution for sum of Wishart Matrices with scale matrices proportional to identity
Consider the independent $n\times p$ dimensional matrices $\mathbf{X}_i, i=1,...,G$, from the matrix variate normal distribution, $N_{n,p}\left(0,\mathbf{I}_n, \mathbf{\Sigma}_i\right)$:
$$P_i\left(\...
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What is the correct form of Metropolis Hasting step in scaled Inverse Wishart prior for covariance matrix?
I was going through the paper of O'Malley and Zaslavsky (2008) for the scaled inverse Wishart priors for a covariance matrix, in order to write an R-code for hierarchical Bayesian estimation of mixed ...
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When are $X^tC_1 X$ and $X^tC_2X$ independent?
Let $X$ be a $n\times p$ data matrix from $N_p(0,\Sigma)$. Let $C_1$ and $C_2$ be two symmmetric idempotent matrices. When are $X^tC_1 X$ and $X^tC_2X$ independent?
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Reconciling Wishart mean and Inverse-Wishart mean
The Inverse-Wishart wikipedia article states that
$ X \sim \operatorname{Wish}^{-1}(\Psi,\nu)$ if $X^{-1} \sim \operatorname{Wish}(\Psi^{-1},\nu),$ where $\Psi$ and $X$ are $p\times p$.
The mean ...
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Wishart Conditional
I am looking for the conditional probability of a Wishart distribution, i.e., if I have a Wishart distributed variable $ S \sim W(\Sigma,n), $ where
$$ S = \begin{bmatrix} S_1 \quad S_{12} \\ S_{21} ...
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The multivariate normal distribution has the same relationship with the Wishart distribution as the multivariate t-distribution with the ...?
Is there a name for the distribution resulting from the sum of outer products of t-distributed random vectors?
Alternatively, is there a matrix-valued distribution with the support of positive ...
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Informative prior for Normal-Inverse Wishart distribution
In Bayesian analysis we use the Normal-Inverse Wishart distribution for the parameters of multivariate models these prior distributions have some hyperparameters. So how do we find the values of ...
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Prior distribution importance in Bayesian inference
I am performing a Bayesian multivariate regression, and therefore I have to construct the prior and the subsequent posterior.
But the paper that I am using as a reference, uses a "Uninformative prior"...
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