The base data structure for the datum of a Simulation Node.
The optional properties contained in this data structure are internally assigned
by the Simulation upon (re-)initialization.
When defining a data type to use for node data, it should be an extension of this interface
and respect the already "earmarked" properties used by the simulation.
IMPORTANT: Prior to initialization, the following properties are optional: index, x, y, vx, and vy.
After initialization they will be defined. The optional properties fx and fy are ONLY defined,
if the node's position has been fixed.
The base data structure for the datum of a Simulation Node. The optional properties contained in this data structure are internally assigned by the Simulation upon (re-)initialization.
When defining a data type to use for node data, it should be an extension of this interface and respect the already "earmarked" properties used by the simulation.
IMPORTANT: Prior to initialization, the following properties are optional: index, x, y, vx, and vy. After initialization they will be defined. The optional properties fx and fy are ONLY defined, if the node's position has been fixed.