collatz weirdness

<?php

$upto = 2000000;
// change the value of THIS specific variable to graph up to some value (originally 2000000).
// also, don't try any lower than 26000. there wouldn't be even a single point.

function collatz($x) {
    if ($x % 2 == 0) {
        return $x/2;
    } else {
        return 3*$x+1;
    }
}

$t = 0;
$x = 0;
$f = "";

for ($i = 1; $i <= $upto; $i++) { // $i is basically the variable x the plot is based upon.
    $j = $i;
    while ($j > 1) {
        $j = collatz($j);
        if ($j == 5) {
            $t += 1; // t at $i = x is N(x).
        }
    }
    $x += $t/$i; // the ratio N(x)/x.
    print "($i) " . ($x/$i) . "\n"; // you can remove this line, this only displays every single value of N(x)/x.
    if ($i % 1000 == 0) { // this would take too long to graph otherwise, but you can remove it if you're an absolute madman.
        $f .= "<div style='position: absolute; left: " . ($i/1000) . "px; bottom: " .

        ($x/$i*((10-900)/(0.93701840707864 - 0.93766121527656))+(10-0.93701840707864*((10-900)/(0.93701840707864 - 0.93766121527656))))
        // zooms such that the local minimum of the curve falls at 10px from the bottom and the maximum at 900px from it.
        // you can, of course, replace 900 by something else if your screen resolution is different.

        . "px'>.</div>\n";
    }
}
file_put_contents("full.html", $f); // the graph will be exported into "full.html" in the same folder as where this file is.

?>