Pi - PHPBuilder Forums

Pi

Harriscat

Hey Everyone,

I am looking for something to run on my webserver that will continualy calculate pi and then export it as a .php etc. file that people will be able to view on my website

Charlie

sys4dm1n

Try something like this:


<?php

function bcpi() {
   $r=2;
   $i=0;
   $or=0;

   while(bccomp($or,$r)) {
       $i++;
       $or=$r;
       $r = bcadd($r,bcdiv(bcmul(bcpow(bcfact($i),2),
                       bcpow(2,$i+1)),bcfact(2*$i+1)));
   }

   return $r;
}

?>

Harriscat

Hey

Thanks very much

When save that and try to open it from my browser it dosent display anything?

Charlie

sys4dm1n

<?php

function bcpi() {
   $r=2;
   $i=0;
   $or=0;

   while(bccomp($or,$r)) {
       $i++;
       $or=$r;
       $r = bcadd($r,bcdiv(bcmul(bcpow(bcfact($i),2),
                       bcpow(2,$i+1)),bcfact(2*$i+1)));
   }

   return $r;
}

print $r;

?>

maddog720

Doesn't work for me, but I'm not much of a pro at php.

Parse error: syntax error, unexpected T_VARIABLE in D:\hshome\adrm23i\antidrm.org\123.php on line 4

sys4dm1n

I have to go now but ill take another look at it in a few hours.

ClarkF1

There is some code here which works:
http://www.planetsourcecode.com/vb/scripts/ShowCode.asp?txtCodeId=1801&lngWId=8

brandtj

This is something I cooked up:

<?php

function atan_inf ($a, $digs) {
	$o = $a;

for ($r = 3; $r <= 99; $r = $r + 2) {
	$a = bcadd ($a, bcmul (((($r - 1) / 2) % 2 == 0 ? 1 : -1), (bcdiv (bcpow ($o, $r, $digs), $r, $digs)), $digs), $digs);
}

return $a;
}

function bcpi ($deep) {
	return bcsub (bcmul (16, atan_inf (1 / 5, $deep), $deep), bcmul (4, atan_inf (1 / 239, $deep), $deep), $deep);
}

echo bcpi (500000);

?>

I sort of made it like sys4dm1n's, but I bug-checked this one already. 😃 Using this code, I calculated pi successfully to 500,000 digits in about 10 seconds. Pretty decent I say. thumbs up

Weedpacket

But it goes wonky from the 16th digit on (3.1415926535897933936727900868262971683628 instead of 3.1415926535897932384626433832795028841791...)

sys4dm1n

@ Weedpacket -- could be some inconsistencies. Verifying with http://www.joyofpi.com/pi.html (changing 500000 to 10000) shows that they are not similar at all.

Weedpacket

Well here are a couple of π generators I put together. Both have the advantage that they can produce digits while they're running, instead of you having to wait until the end. There are two because there are advantages and disadvantages to them.

The first one starts out slow but speeds up as it proceeds; it also needs the number of digits required to be specified in advance (so that it can allocate space for them). The supplied code sez 2400 digits.

The second could probably do with some more optimisation; it's not exactly fast, but it will keep cranking out digit after digit for as long as you're prepared to put up with it (or it needs to be upgraded so that lfts() uses bc arithmetic to generate the next array!).

NOTE: I'm not 100% certain these are correct. recommend you check against an existing expansion (which, if that's all your after, would proably be a better solution anyway!).

Even better might be a native executable to calculate the digits, and call it from the command line (something from http://home.istar.ca/~lyster/pi.html perhaps).

$size = 4*2400;
$e = 0;
$f = array_fill(0, $size, 2000);
for($c=$size-1; $c>=0; $c-=14)
{
	$d = 0;
	for($b=$c; $b>0; --$b)
	{
		$g = 2*$b-1;
		$d = $d*$b+$f[$b]*10000;
		$f[$b] = $d%$g;
		$d = intval($d/$g);
	}
	printf('%04u',($e+$d/10000));
	$e = $d%10000;
}

function extr($qrt,$x)
{
	return bcdiv(bcadd(bcmul($q,$x),$r),$t);
}

function gcd($a,$b)
{
	if($a[0]=='-') $a = substr($a,1);
	if($b[0]=='-') $b = substr($b,1);
	while(bccomp($b,0))
	{
		$nb = bcmod($a,$b);
		$a = $b;
		$b = $nb;
	}
	return $a;
}

function comp($qrt, $uvx)
{
	static $rescale=0;
	list($q,$r,$t) = $qrt;
	list($u,$v,$x) = $uvx;
	$a = bcmul($q,$u);
	$b = bcadd(bcmul($q,$v),bcmul($r,$x));
	$d = bcmul($t,$x);
	if($rescale==10)
	{
		$gcd = gcd(gcd($a,$b),$d);
		if($gcd!=1)
		{
			$a = bcdiv($a,$gcd);
			$b = bcdiv($b,$gcd);
			$d = bcdiv($d,$gcd);
		}
		$rescale = 0;
	}
	else
	{
		$rescale++;
	}
	return array($a,$b,$d);
}
function lfts()
{
	static $k=1;
	$return = array($k, 4*$k+2, 2*$k+1);
 	$k++;
	return $return;
}

function do_pi()
{
	$z = array(1,0,1);
	while(true)
	{
		$y = intval(extr($z, 3));
		if($y==intval(extr($z, 4)))
		{
			echo $y;
			$z = comp(array(10, -10*$y, 1), $z);
		}
		else
		{
			$z = comp($z,lfts());
		}
	}
}

do_pi();

Harriscat

Thanks everyone for these great scripts! Is there anyway that i can keep one constantley running so people can check back to see how far the Pi has calculated

Charlie

sys4dm1n

That seems more like a javascript function.

Harriscat

Is this still possible to do?

Weedpacket

I wouldn't see it as a Javascript function; we're talking about calculating π on the server, right?

If that's the way it's operating, I'd definitely go for a native executable program. Start it running, redirect its output to a file, and then the PHP script can read the file (if it's stored as simply as possible - just digits 0-9, no punctuation, etc., then the size of the file would be the number of digits so far generated). Right now I don't have a link to a suitable program (the second script I posted works as required, but you might want something faster - and if you want fast you want machine code).

sys4dm1n

Weedpacket, I thought he was talking about being able to see the digits in real time move, etc -- like what google has going on with the gmail account size.

Harriscat

So that secound script of yours will work like the one i am looking for?

Charlie

Weedpacket

sys4dm1n wrote:
Weedpacket, I thought he was talking about being able to see the digits in real time move, etc -- like what google has going on with the gmail account size.

That's not how I read it; it sounded like there was going to be one process generating digits, and visitors would see how far the computer had got.

Harriscat wrote:
So that secound script of yours will work like the one i am looking for?

Weedpacket wrote:
...the second script I posted works as required, but you might want something faster...

Harriscat

Thanks I will try the secound script on my webserver and see how it goes. How much strain is this likely to put on my webserver?

Charlie

Weedpacket

More and more as time goes by: since the number is irrational, memory requirements will increase over time.

Another thing you might think of doing is using one of those apps and ask for the first 1000 digits. Save them. Then run it again asking for the first 2000. Save them. Sure, you're doing quadratically more work (by the time you get to 1,000,000 digits you've calculated the first thousand 1000 times, the second thousand 999 times...) but you'll get there a lot quicker (hang on a tick: 500,000 digits in under two seconds, and 10,000,000 in a minute.)