Ariarule

<?php
function rack_block_shooter($opponents_last_move = NULL, $round = 0) {
//returns TRUE for cooperate
//FALSE for defect
//in most loops, $i is the currently considered frequency of cooperation
static $probs = array();
static $prev_strat;
static $maybe_playing_self;

if ($round == 0) {
//setup probability arrays
//first key is our previous move
//second keys are frequency of opponent's coop
$probs = array(); //reset probabilities for first round of a match
$maybe_playing_self = TRUE;
for ($i = 0.00; $i <= 1.00; $i += 0.01) {
$probs[TRUE][(string)$i] = 1 / 101;
$probs[FALSE][(string)$i] = 1 / 101;
}
$prev_strat = FALSE; //Start with Defection to make self-indent slightly easier, defection as sign of a good/nice strategy -- therefore prob. other LWers more likely to start with coop; Also immediately sorts out Tit-for-Tat
}
else {
//update probs
if ($maybe_playing_self) {
if ($prev_strat != $opponents_last_move) {
//are we playing against ourselves?
$maybe_playing_self = FALSE; //Not if both sides don't make the same move
}
}
$prob_see_coop = 0.00;
for ($i = 0.00; $i <= 1.00; $i += 0.01) {
//the probability we would see cooperation given our move
$prob_see_coop += ($probs[$prev_strat][(string)$i] * $i);
}
for ($i = 0.00; $i <= 1.00; $i += 0.01) {
if ($opponents_last_move) {
//opp coop
$probs[$prev_strat][(string)$i] = $i * $probs[$prev_strat][(string)$i]/$prob_see_coop;
}
else {
//opp defect
$probs[$prev_strat][(string)$i] = (1 - $i) * $probs[$prev_strat][(string)$i]/(1 - $prob_see_coop);
}
}

//Now, decide what to do
if ($round == 1) {
//second round, do the opposite of whatever we did the first round
$prev_strat = !$prev_strat;
}
else {
//middle of play, choose move randomly proportional to expected payout
//Begin by calc'ing the prob of coop again for both cooperation and defection
$prob_see_coop = array();
$prob_see_coop[TRUE] = 0.00; //the probability we'll see coop if we coop
$prob_see_coop[FALSE] = 0.00;  //the probability we'll see coop if we defect
for ($i = 0.00; $i <= 1.00; $i += 0.01) {
$prob_see_coop[TRUE] += ($probs[TRUE][(string)$i] * $i);
$prob_see_coop[FALSE] += ($probs[FALSE][(string)$i] * $i);
}
file_put_contents('updating.txt', implode("\t\t",array(implode("\t",$probs[TRUE]),implode("\t",$probs[FALSE])))."\n", FILE_APPEND);
if ($maybe_playing_self) {
$prev_strat = TRUE;
}
else {
if ($round == 99) {
//be slightly evil -- always defect on the last round if not playing against self
$prev_strat = FALSE;
}
else {
$expected_value = array();
$fudge_factor = 0; //roughly, how much do we dislike the other player
$expected_value[TRUE] = 4 * $prob_see_coop[TRUE]; //+ 0 * (1 - $prob_see_coop[TRUE]); 
$expected_value[FALSE] = 7 * $prob_see_coop[FALSE] + 1 * (1 - $prob_see_coop[FALSE]);
$total_exp = array_sum($expected_value);
$prop_coop = ($expected_value[TRUE] - $expected_value[FALSE])/$total_exp;
$choose_mixed = lcg_value(); //random in the range (0,1) -- differs from rand() as rand generates integers only

if ($expected_value[FALSE] > 1.5 * $expected_value[TRUE]) {
$prev_strat = FALSE;
}
elseif ($expected_value[TRUE] > 1.5 * $expected_value[FALSE]) {
$prev_strat = TRUE;
}
else {
if ($choose_mixed <= $prop_coop) {
$prev_strat = TRUE;
}
else {
$prev_strat = FALSE;
}
}
}
}
}
}
return $prev_strat;
}