Define the continuous state vector $\mathbf{x}(t)$ and its governing derivative $\frac{d\mathbf{x}}{dt} = \mathbf{f}(\mathbf{x}, t)$.
2. Execution Block & Constraints
Configure the temporal domain and accuracy invariants.
3. Results (Dense Output)
Awaiting simulation execution...
Rheo Philosophy Note: This interface models the core principle: defining the *derivative* ($\frac{dx}{dt}$) is the primitive, not the accumulation of steps. The system relies on Automatic Differentiation (AD) and Dynamic Method Selection to guarantee the Accuracy Invariant ($|\text{LTE}| \leq \max(\text{atol}, \text{rtol} \cdot |x|)$).