Generally, in an ALIEN simulation, all bodies as well as thermal radiation are modeled by different types of particles. The following terms are frequently used in this documentation.
An ALIEN world is two-dimensional rectangular domain with periodic boundary conditions. The space is modeled as a continuum.
Cells are a type of particles which serve as matter building blocks and which are able to connect to each others. One can think of cells as nodes of a graph embedded in a 2D space. Moreover, cells possess physical properties such as
- Position in space
- Internal energy (corresponding to its temperature)
- Upper limit of connections
and a specialization together with an internal state (e.g. memory, color).
A cell connection is a bond between two cells. It stores the reference distance and on each side a reference angle to a previous cell connection. The reference distance and angles are calculated when the connection is established. As soon as the actual distance is greater than the reference distance, a pulling force is applied at both ends. Conversely, a pushing force occurs when it is less. The forces are linear with respect to the deviation. In the same sense, tangential forces are applied at both ends in the case of an angle mismatch.
Each cell has a special function that can be triggered and (usually) accepts certain inputs and returns output values. Currently, the following functions are implemented:
- Computation: It allows the execution of 15 lines of assembler-like code. The code has access to the memories of the cell and token (see below).
- Construction: It can create a new cell with or without a connection to the host cell.
- Digestion: It converts a surrounding cell to internal energy under certain conditions.
- Sensor: It scans the vicinity or a particular direction for concentration of particles with a certain color.
- Muscle: It can contract or expand a cell connection. During this process, it can generate a momentum.
- Scanner: It enables self-inspection of cell structures starting from the host cell. A scanner determines the specialization and state of other cells. Also the reference distance and angles of connecting cells are detected.
A cell cluster (or cluster for short) is connected graph consisting of cells and cell connections. Two cells in a cluster are therefore connected to each other directly or via other cells. A cluster physically represents a particular body.
An energy particle is a particle which has only an energy value, position and velocity. Unlike cells, they cannot form clusters or perform any additional functions. Energy particles are produced by cells as radiation or during decay and can, in turn, also be absorbed.
A token is an entity which is located on a cell and which as a state and an energy value. Its purpose is to transmit information from cell to cell and to carry out cellular functions. A token does not remain on its cell, but jumps after each time step to connected cells or will be destroyed.
A pattern is a set of cell clusters or energy particles.