random-boolean-network/random_boolean_network.php

<?php

/*
    Random boolean network in PHP (7.4+).
    Inspired by the Computerphile Video: https://www.youtube.com/watch?v=mCML2B94rUg

    Joop Schilder
    Fri 13 Nov
*/

const NUM_NODES = 20;
const NUM_CONNECTIONS = 3;
const NUM_GENERATIONS = 20;

const CHAR_ON_ZERO = '0';
const CHAR_ON_ONE = ' ';

const TRUTH_TABLE_SIZE = (1 << NUM_CONNECTIONS);


$truth_table = [];
for ($i = 0; $i < TRUTH_TABLE_SIZE; $i++) {
    $truth_table[$i] = random_int(0, 100) % 2;
}

$nodes = [];
for ($i = 0; $i < NUM_NODES; $i++) {
    $nodes[$i] = random_int(0, 100) % 2;
}

$connections = [];
for ($i = 0; $i < NUM_NODES; $i++) {
    for ($j = 0; $j < NUM_CONNECTIONS; $j++) {
        $connections[$i][$j] = random_int(0, 2000) % 20;
    }
}

function print_generation(int $g, array $nodes): void
{
    printf("G%5d   %s\n", $g, format_nodes($nodes));
}

function print_truth_table(array $truth_table): void
{
    print("Truth table:\n");
    for($i = 0; $i < TRUTH_TABLE_SIZE; $i++) {
        printf("[%s] => %d\n", str_pad(decbin($i), NUM_CONNECTIONS, '0', STR_PAD_LEFT), $truth_table[$i]);
    }
}

function print_connections(array $connections): void
{
    print("Connections:\n");
    for ($i = 0; $i < NUM_NODES; $i++) {
        printf("[%3d] => [%s]\n", $i, implode(', ', $connections[$i]));
    }
}

function format_nodes(array $nodes): string
{
    return implode(' ', array_map(fn($i): string => $i == 0 ? CHAR_ON_ZERO : CHAR_ON_ONE, $nodes));
}

function propagate(array $nodes, array &$connections, array &$truth_table): array
{
    $next_nodes = [];
    for ($i = 0; $i < NUM_NODES; $i++) {
        $tt_index = 0;
        for ($j = 0; $j < NUM_CONNECTIONS; $j++) {
            $tt_index += $nodes[$connections[$i][$j]] << (NUM_CONNECTIONS - 1 - $j);
        }
        $next_nodes[$i] = $truth_table[$tt_index];
    }

    return $next_nodes;
}

print_truth_table($truth_table);
print("\n");

print_connections($connections);
print("\n");

print_generation(0, $nodes);
for ($i = 0; $i < NUM_GENERATIONS; $i++) {
    $nodes = propagate($nodes, $connections, $truth_table);
    print_generation($i, $nodes);
}