expm1

(PHP 4 >= 4.1.0, PHP 5)

expm1 — Returns exp(number) - 1, computed in a way that is accurate even when the value of number is close to zero

Descrierea

float expm1 ( float $arg )

expm1() returns the equivalent to 'exp(arg) - 1' computed in a way that is accurate even if the value of arg is near zero, a case where 'exp (arg) - 1' would be inaccurate due to subtraction of two numbers that are nearly equal.

Parametri

arg: The argument to process

Valorile întoarse

'e' to the power of arg minus one

Istoria schimbărilor

Versiunea	Descriere
5.3.0	This function is now available on all platforms

Vedeți de asemenea

log1p() - Returns log(1 + number), computed in a way that is accurate even when the value of number is close to zero
exp() - Calculates the exponent of e

add a note User Contributed Notes
expm1

brettz9 AAT yah
03-Apr-2009 04:07


Note that exp(x)-1 can be approximated by x + x^2/2! + ... + x^n/n!  and for any value

hagen at von-eitzen dot de
24-Feb-2003 11:57


Compare this to log1p (which is its inverse).





Also, You may have to use a similar workaraound in case the underlying C library


does not support expm1:





<?php


function expm1($x) {


     return ($x>-1.0e-6 && $x<1.0e-6) ? ($x + $x*$x/2) : (exp($x)-1);


}


?>

add a note

floor

exp

Last updated: Fri, 25 Jun 2010