# The Matrix-Gaussian distribution

Gupta and Nagar (1999):

The random matrix $$X(p \times n)$$ is said to have a matrix variate normal distribution with mean matrix $$M(p \times n)$$ and covariance matrix $$\Sigma \otimes \Psi$$ where $$\Sigma(p \times p)>0$$ and $$\Psi(n \times n)>0$$, if $$\operatorname{vec}\left(X^{\prime}\right) \sim N_{p n}\left(\operatorname{vec}\left(M^{\prime}\right), \Sigma \otimes \Psi\right)$$

We shall use the notation $$X \sim N_{p, n}(M, \Sigma \otimes \Psi)$$.

They prove the following theorem:

If $$X \sim N_{p, n}(M, \Sigma \otimes \Psi)$$, then the p.d.f. of $$X$$ is given by $\begin{array}{r} (2 \pi)^{-\frac{1}{2} n p} \operatorname{det}(\Sigma)^{-\frac{1}{2} n} \operatorname{det}(\Psi)^{-\frac{1}{2} p} \operatorname{etr}\left\{-\frac{1}{2} \Sigma^{-1}(X-M) \Psi^{-1}(X-M)^{\prime}\right\} \\ X \in \mathbb{R}^{p \times n}, M \in \mathbb{R}^{p \times n} \end{array}$

## References

Gupta, A. K., and D. K. Nagar. 1999. Matrix Variate Distributions. Chapman & Hall/CRC Monographs and Surveys in Pure and Applied Mathematics 104. Boca Raton: Chapman and Hall/CRC.
———. 2018. Matrix Variate Distributions. CRC Press.

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