Pressio is applicable to any system expressible in a continuous-time form as
or in time-discrete form as
In the time-continuous case, denotes the state and denotes the velocity that may be linear or nonlinear in its first argument. In the time-discrete case, denotes the state at the current time instance, denotes the state at the i-th previous time instance, and denotes the time-discrete residual arrising, for example, from a linear mulstistep method.
We note that the model form above is highly expressive, as it may be derived from the spatial discretization of a PDE problem or from naturall discrete systems (e.g., molecular-dynamics problems).