### Modeling concepts

- Three basic approaches:
- hybrid decomposition
- two subsystems for phases "swinging" and
"falling"
- have different state space dimensions
- "swinging" phase uses angle φ, ω
- "falling" phase uses cartesian coordinates x,
y, vx, vy
- global switch activates/deactivates
subsystems

- maximal state space
- contains all variables φ, x, y and
derivatives
- unused variables are "frozen"

- high index DAE using cartesian coordinates only
- constraint equation changes

- Equation-based solution in Modelica:
- seems hopeless in Modelica, since total equation count
is constant
- implementation straightforward
- seems easy, but doesn't work