# Difference between revisions of "Totalistic Life-like cellular automaton"

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## Revision as of 10:03, 9 July 2017

**Totalistic Life-like cellular automaton** can refer to two related but distinct classes of cellular automata.

Most precisely, a Life-like cellular automaton is said to be **totalistic** if the new state of a (live or dead) cell in the next generation can be expressed as a function of the total number of live cells in its neighborhood, including the cell itself.

In common parlance, **totalistic** is also often (but incorrectly) used as a synonym for **outer-totalistic / semi-totalistic**, meaning that the new state of a cell is a function of both the total number of live cells surrounding the cell, and the state of the cell itself. The rest of this article will use the previous, precise definition.

The two definitions differ in that in the second case, the transition function may afford special consideration to the state of the cell itself. For example, the following two configurations may evolve differently in an outer-totalistic CA, but must be treated the same by a totalistic CA:

There are precisely 2^{9} = 512 different totalistic CAs, compared to 2^{18} = 262,144 outer-totalistic CAs.^{[note 1]}

A given outer-totalistic Life-like CA is totalistic iff for any 1 ≤ *n* ≤ 8, a live cell survives with *n - 1* neighbors iff a dead cell gets born with *n* neighbors. For example, the automaton given by the rulestring B3/S2 is totalistic; any cell will be alive in the next generation if it has exactly three live cells (including the cell itself) in its neighborhood, and dead otherwise. Conway's Game of Life (B3/S23), on the other hand, is not totalistic: a live cell with three neighbors will survive to the next generation, but a dead cell with four neighbors will not get born.

## Etymology

The word *"totalistic"* stems from the fact that evolution in a totalistic CA depends only on the *total* number of live cells in a given cell's neighborhood; similarly, in *outer-totalistic* CAs, evolution depends on the *total* number of *outer* cells, rather than their specific alignment. The word "*semi-totalistic*" expresses that an outer-totalistic CA, while not necessarily totalistic, is not entirely non-totalistic either: the transition function still depends on some certain total number of live cells.

## Generalizations

Totalistic and outer-totalistic CAs can be generalized in several straightforward ways: taking into account the relative (but not absolute) alignment of live cells in a cell's neighborhood yields non-totalistic (isotropic) CAs, while also considering the absolute alignment yields non-isotropic CAs.

## Also see

- Cellular automaton
- Non-totalistic Life-like cellular automaton
- Non-isotropic Life-like cellular automaton
- Generations
- Larger than Life

## Notes

- ↑ Although there 262,144 different outer-totalistic Life-like CAs, some of these are essentially the same in some precise sense. See Cellular automaton for more.

## External links

- Totalistic Cellular Automaton at Wolfram Mathworld