expm1

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

expm1 返回 exp(number) - 1,甚至当 number 的值接近零也能计算出准确结果

说明

expm1(float $num): float

expm1() 返回“exp(num) - 1”,甚至当 num 的值接近零也能计算出准确结果。但是当两个数值趋近于相等的时候,“exp (num) - 1”就会变得不太准确。

参数

num

要处理的参数

返回值

“e”的 num 次方减 1

参见

  • log1p() - 返回 log(1 + number),甚至当 number 的值接近零也能计算出准确结果
  • exp() - 计算 e 的指数

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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
13 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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