Bivariate Gaussian

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The bivariate Gaussian can be written as:


f(x,y)
=
\frac{1}{2 \pi \sigma_x \sigma_y \sqrt{1-\rho^2}}
\exp
\left(
 -\frac{1}{2 (1-\rho^2)}
 \left[
  \frac{\left(x - \mu_x\right)^2}{\sigma_x^2} +
  \frac{\left(y - \mu_y\right)^2}{\sigma_y^2} -
  \frac{2 \rho \left(x - \mu_x\right) \left(y - \mu_y\right)}{ (\sigma_x \sigma_y)}
 \right]
\right)

where ρ is the correlation between X and Y. In other words


\Sigma =
\begin{bmatrix}
\sigma_x^2              & \rho \sigma_x \sigma_y \\
\rho \sigma_x \sigma_y  & \sigma_y^2
\end{bmatrix}.
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