function stat_correlp($data1, $data2)
{
//calculates the population correlation
//arrays must be same size
$covarp = stat_covarp($data1, $data2);
$stdevp1 = stat_stdevp($data1);
$stdevp2 = stat_stdevp($data2);
return $covarp / ($stdevp1 * $stdevp2);
}
$sSlice = array_slice($s[$key]['changes'], $i, 156);
if (count($sSlice) >= 156) {
$s[$key][$t][$date] = stat_correlp($sSlice, array_slice($m[0]['changes'], $i, 156));
$i++;
}
}
}
break;
case 'stdev':
foreach ($s as $key => $stock) {
$i = 0;
foreach ($stock['changes'] as $date => $change) {
$sSlice = array_slice($s[$key]['changes'], $i, 156);
if (count($sSlice) >= 156) {
//only calculate when 156 weeks of data exist
$s[$key][$t][$date] = stat_stdevp($sSlice) * sqrt(52);
$i++;
}
}
}
break;
default:
$t = 'beta';
foreach ($s as $key => $stock) {
$i = 0;
foreach ($stock['changes'] as $date => $change) {
$sSlice = array_slice($s[$key]['changes'], $i, 156);
if (count($sSlice) >= 156) {
//only calculate when 156 weeks of data exist
$s[$key][$t][$date] = stat_covarp($sSlice, array_slice($m[0]['changes'], $i, 156)) / stat_varp(array_slice($m[0]['changes'], $i, 156));
$i++;
