exp returning zero

[dingus]

hey i have a small problem with the exp function

 

basically its dealing with a relay small number (in the order of 1.2E-300)

 

problem is when i pass that number to the exp function it is returning zero

 

is there a way to get around it?

[rhodesa]

I can't reproduce the problem. Can you provide a sample of code?

[dingus]

ok have have an inverse chi square distribution block

 

that looks like this

 

<?php

function inv-chi2( $x,  $v) {
        $m = (double)$x / 2.0;
        $s = exp(-$m);
        $t = $s;
        
        for($i=1; $i < ($v/2);$i++) {
            $t *= $m/$i;
            $s += $t;
        }
        return ( $s < 1.0) ? $s : 1.0;
    }

?>

 

i know its not perfect butt it worked

 

now ging into that the value of

 

$x = 1895.74465264

and

$v = 2468

 

when we get to the exp function

$m = 947.872326318

 

how ever after exp(-$m);

 

$s becomes zero

 

anyone have any ideas there?

[Fadion]

If i made the right calculations, the result of exp(-$m) where $m = 1895.74465264 / 2 is ~ 2.19e412, but from the manual:

 

The size of a float is platform-dependent, although a maximum of ~1.8e308 with a precision of roughly 14 decimal digits is a common value (the 64 bit IEEE format).

 

Guess thats why ure getting 0 as a result.

[dingus]

well at least now i know why im geting zero next question is how to get somthing that isnt zero anyone have any ideas on that