PHP中的Erlang-B公式求和

Question

I've tried to port the following sum in a php for loop

this way:

    $prod = 1;

for($i=0;$i<$_POST["capacity"];$i++){
$prod = $prod * (($_POST["capacity"] - (i+1)) / $toffered);
} 
    ?>
p(c) is:  <?php echo floatval(1.00/floatval((1+ floatval($prod)))); ?><br /> <br />

but for some reason it seems to give me the wrong result. Any hints on what is wrong?

EDIT : i've modified the initial value of prod as well as adding brackets for i+1 which is subtracted from the capacity. The results aren't better still.

Answer 1

I think you are actually not doing the sum, only the product part (the dots ...).

If I'm not mistaken, you'll need 2 nested loops here, one for i = 1 to c (computing the sum), and one for 1 to i (computing the product).

Answer 2

$prod = 0.0;

for($i=1;$i<$capacity;$i++){
$prod = (1.0 + $prod) * (floatval($i) / $toffered);
}
?>

p(c) is:  <?php echo (1.0 / ( 1.0 + $prod)); ?> %

works!