In this paper we propose a C++-software package implementing the algorithm EKF-AUS-NL (Extended Kalman Filter with Assimilation in the Unstable Space with NonLinear evolution) designed to perform data assimilation in the unstable space when the Jacobian of the differential equation cannot be calculated. We also propose a simple approach to take into account the presence of the model e... https://foldlyers.shop/product-category/covert/