okay im not joking there is no e i AM talking about the infinant number which is used to calculate many aspects of circles.

So how can i generate Pi with PHP?

*Yes i do already know that if i didnt properly code it to have a cut off it will eventually over load my server and crash (if it didnt have precautions) but i know it would definatly muck up my home testing server

So how can i generate it? i would like to be able to get it into a function like

pi(Number of decimal places i want to show)

So how can i do it?
--edit--
just found this so how can i do that but to how ever many decimal places i want?

http://uk.php.net/pi

http://uk.php.net/manual/en/function.round.php

PHP Code:

echo (round(pi(),$No_of_decimal_places)); 


from a comment on the page on php.net for pi() he said it could only go to 20 decimal places?

Did someone say Pie? Oh PI. Never mind.

Dan PI = 22/7. You could set a variable PI = 22.0/7.0

I know that you can not do this with c++ due to overflow on longs (once you reach a really large number it starts over at a negative number). Would this not also be the same for PHP?

http://en.wikipedia.org/wiki/Floating_point

Is calculating Pi necessary - are you doing some sort of server benchmark test.

If not then surely 22/7 would be sufficient - most engineers will only use pi to 6 decimal places at most.

Originally Posted by vangogh

Did someone say Pie? Oh PI. Never mind.

Dan PI = 22/7. You could set a variable PI = 22.0/7.0

Im sorry steve but 22/7 is most definatly NOT pi.

firstly it may work out to 3.14**

but it has a recoring pattern which makes it a rational number where as pie is a irrational number with no pattern what so ever....

Anyway, im now bit confuse if this is possible because form the php docs it seems to imply there is a limit but im just erm confused

Dan, my bad, but believe it or not that's how I originally learned it in school. Of course that is based on my memory of an event that's now close to 30 years ago so what I learned may have been meant as an approximation.

Is there a reason you need beyond 20 decimal places?

Dan: Check this out http://en.wikipedia.org/wiki/Pi#Calculating_.CF.80 . That article explains how to accurately calculate pi.

Chris: Floating points can still overflow.(At least in my experience.)

From what I've read PHP only allows 20 decimal places of precision on any number.

For good reason I would assume - 20 d.p. is a lot of precision.

Why cant this just have a simple answer? Lol

for the sake of argument say i want to work out pi to as many places as i can.

so would there be a way to write a loop which works out each point, pauses to try and be kind of the server running it, and keep appending the decimal to our Pi figure?

so we could have while pi is less than X long keep working out more, or just have it as a infinant loop. but have it save to a database/file so it dont keep working them all out each time its displayed.

am i making any sense, because this sounds easy to me, if i had the calculation to work it out.

Why cant this just have a simple answer?

There isn't a simple answer to pi, in fact there isn't an answer to pi

with php you are limited to a precision of 20 digits anyway, but here's a few formulas if you want to code the calculation

http://www.math.com/tables/constants/pi.htm

Yes floating point numbers can overflow, at what point is dependant on the OS implementation

PHP Code:

//bcpi function with Gauss-Legendre algorithm
//by Chao Xu (Mgccl)
function bcpi($precision){
    $limit = ceil(log($precision)/log(2))-1;
    bcscale($precision+6);
    $a = 1;
    $b = bcdiv(1,bcsqrt(2));
    $t = 1/4;
    $p = 1;
    while($n < $limit){
        $x = bcdiv(bcadd($a,$b),2);
        $y = bcsqrt(bcmul($a, $b));
        $t = bcsub($t, bcmul($p,bcpow(bcsub($a,$x),2)));
        $a = $x;
        $b = $y;
        $p = bcmul(2,$p);
        ++$n;
    }
    return bcdiv(bcpow(bcadd($a, $b),2),bcmul(4,$t),$precision);
};

echo bcpi(75);// pi to 75 decimal places 3.141592653589793238462643383279502884197169399375105820974944592307816406286 


Why you need to calculate PI? It's a constant; its' value will never change.

Can't you define a constant containing PI? Then, you can round it at as many demical places as you want.

Originally Posted by maxxximus

PHP Code:

//bcpi function with Gauss-Legendre algorithm
//by Chao Xu (Mgccl)
function bcpi($precision){
    $limit = ceil(log($precision)/log(2))-1;
    bcscale($precision+6);
    $a = 1;
    $b = bcdiv(1,bcsqrt(2));
    $t = 1/4;
    $p = 1;
    while($n < $limit){
        $x = bcdiv(bcadd($a,$b),2);
        $y = bcsqrt(bcmul($a, $b));
        $t = bcsub($t, bcmul($p,bcpow(bcsub($a,$x),2)));
        $a = $x;
        $b = $y;
        $p = bcmul(2,$p);
        ++$n;
    }
    return bcdiv(bcpow(bcadd($a, $b),2),bcmul(4,$t),$precision);
};
 
echo bcpi(75);// pi to 75 decimal places 3.141592653589793238462643383279502884197169399375105820974944592307816406286 


Thanks for this so far this seems to be accurate, im currently running a simple if the pi generated with the function matched pi i copied from the pi website matches. and because it trying to match it to a measly million points its taking a while...

Lol

Thanks for this, only one more thing, would there be some way to be able to have it work out to X places save the figure somewhere or the amount of places, and then be able to get it to work out more without it having to work out the first X places?
does this make sense?