expm1

(PHP 4 >= 4.1.0, PHP 5, PHP 7)

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

Descrierea

expm1 ( float $num ) : float

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

Parametri

num: The argument to process

Valorile întoarse

'e' to the power of num minus one

A se vedea și

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

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User Contributed Notes 2 notes

down

-1

brettz9 AAT yah ¶

15 years ago


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

down

-1

hagen at von-eitzen dot de ¶

21 years ago


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);

}

?>

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