Von Mises distribution

circular normal distribution

A unimodal probability distribution on the circle with probability density $$ p(\phi) = \frac{1}{2\pi I_0(\kappa)} \exp(\kappa \cos(\phi-\theta_1)) $$ with two parameters, $\kappa$ and $\theta_1$. This function takes its maximum value at $\phi = \theta_1$, so that $\theta_1$ is the mode; $\kappa$ is a concentration parameter.

The von Mises distribution is commonly used in the statistical analysis of directions.