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<?
/* The Computer Language Benchmarks Game
http://shootout.alioth.debian.org/
contributed by Isaac Gouy
modified by anon
*/
function A(&$i, &$j){
return 1.0 / ( ( ( ($i+$j) * ($i+$j+1) ) >> 1 ) + $i + 1 );
}
function Av(&$n,&$v){
global $_tpl;
$Av = $_tpl;
for ($i = 0; $i < $n; ++$i) {
$sum = 0.0;
foreach($v as $j=>$v_j) {
$sum += A($i,$j) * $v_j;
}
$Av[$i] = $sum;
}
return $Av;
}
function Atv(&$n,&$v){
global $_tpl;
$Atv = $_tpl;
for($i = 0; $i < $n; ++$i) {
$sum = 0.0;
foreach($v as $j=>$v_j) {
$sum += A($j,$i) * $v_j;
}
$Atv[$i] = $sum;
}
return $Atv;
}
function AtAv(&$n,&$v){
$tmp = Av($n,$v);
return Atv($n, $tmp);
}
$n = intval(($argc == 2) ? $argv[1] : 1);
$u = array_fill(0, $n, 1.0);
$_tpl = array_fill(0, $n, 0.0);
for ($i=0; $i<10; $i++){
$v = AtAv($n,$u);
$u = AtAv($n,$v);
}
$vBv = 0.0;
$vv = 0.0;
$i = 0;
foreach($v as $val) {
$vBv += $u[$i]*$val;
$vv += $val*$val;
++$i;
}
printf("%0.9f\n", sqrt($vBv/$vv));