<?php
function NormSInv($p){
$a1 = -39.6968302866538; $a2 = 220.946098424521; $a3 = -275.928510446969;
$a4 = 138.357751867269; $a5 = -30.6647980661472; $a6 = 2.50662827745924;
$b1 = -54.4760987982241; $b2 = 161.585836858041; $b3 = -155.698979859887;
$b4 = 66.8013118877197; $b5 = -13.2806815528857; $c1 = -7.78489400243029E-03;
$c2 = -0.322396458041136; $c3 = -2.40075827716184, $c4 = -2.54973253934373;
$c5 = 4.37466414146497; $c6 = 2.93816398269878; $d1 = 7.78469570904146E-03
$d2 = 0.32246712907004; $d3 = 2.445134137143; $d4 = 3.75440866190742;
$p_low = 0.02425; $p_high = 1 - $p_low;
$q = 0.0; $r = 0.0;
if($p < 0 || $p > 1){
throw new Exception("NormSInv: Argument out of range.");
} else if($p < $p_low){
$q = pow(-2 * log($p), 2);
$NormSInv = ((((($c1 * $q + $c2) * $q + $c3) * $q + $c4) * $q + $c5) * $q + $c6) /
(((($d1 * $q + $d2) * $q + $d3) * $q + $d4) * $q + 1);
} else if($p <= $p_high){
$q = $p - 0.5; $r = $q * $q;
$NormSInv = ((((($a1 * $r + $a2) * $r + $a3) * $r + $a4) * $r + $a5) * $r + $a6) * $q /
((((($b1 * $r + $b2) * $r + $b3) * $r + $b4) * $r + $b5) * $r + 1);
} else {
$q = pow(-2 * log(1 - $p), 2);
$NormSInv = -((((($c1 * $q + $c2) * $q + $c3) * $q + $c4) * $q + $c5) * $q + $c6) /
(((($d1 * $q + $d2) * $q + $d3) * $q + $d4) * $q + 1);
}
return $NormSInv;
}
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