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expm1

(PHP 4 >= 4.1.0, PHP 5, PHP 7, PHP 8)

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

Descrição

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.

Parâmetros

num

The argument to process

Valor Retornado

'e' to the power of num minus one

Veja Também

  • log1p() - Returns log(1 + number), computed in a way that is accurate even when the value of number is close to zero
  • exp() - Calcula o expoente de e

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User Contributed Notes 2 notes

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0
hagen at von-eitzen dot de
20 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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-1
brettz9 AAT yah
14 years ago
Note that exp(x)-1 can be approximated by x + x^2/2! + ... + x^n/n! and for any value
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