<?
$a = 1;
$b = 2;
$c = 3;

$types['a'] = array($a,-$a);
$types['b'] = array($b,-$b);
$types['c'] = array($c,-$c);

$combos = combo($types);

for($i=0;$i<count($combos);$i++){
 echo "Row {$i} => {$combos[$i][0]},{$combos[$i][1]},{$combos[$i][2]}".PHP_EOL;
}

function combo($types){
 $t = array_shift($types);

 if(count($types) == 0){
  return $t;
 }
 $c = array();
 $combos = combo($types);
 foreach($t as $z){
  foreach($combos as $combo){
   $combo = is_array($combo) ? $combo : array($combo);
   $c[] = array_merge(array($z),$combo);
  }
 }
 return $c;
}


/* OUTPUT:
Row 0 => 1,2,3
Row 1 => 1,2,-3
Row 2 => 1,-2,3
Row 3 => 1,-2,-3
Row 4 => -1,2,3
Row 5 => -1,2,-3
Row 6 => -1,-2,3
Row 7 => -1,-2,-3