Topology of a Multicellular Organism

In a parallel program, each cell has a specific position in the environment (just like any other cell). The only restrictions on the placement of cells within a parallel program (beyond those defined for all cells by the global parameters) are that every cell within the organism must be adjacent to (i.e. occupy one of the eight neighbouring grid positions) at least one other cell owned by the organism, and that two cells within the same organism cannot share the same grid position. The topology of an organism is important in terms of its intercellular communications, as any given cell can only exchange regulators and energy tokens with immediately adjacent cells within the organism. By means of this transfer between cells in a multicellular organism, the behaviour of any cell is affected by the behaviour of its neighbours. See Section 4.6.1 for more details.

As a parallel program develops, an individual cell can actually change its position relative to its neighbours, using the migrate instruction. This gives a cell the opportunity of interacting with different neighbouring cells throughout the life of the program.