Note that exp(x)-1 can be approximated by x + x^2/2! + ... + x^n/n! and for any value
(PHP 4 >= 4.1.0, PHP 5, PHP 7, PHP 8)
expm1 —
返回 exp($num) - 1
,甚至当 number 的值接近零也能计算出准确结果
expm1() 返回 exp($
,甚至当
num
) - 1num
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($
就会变得不太准确。
num
)
- 1
num
要处理的参数
e
的 num
次方减 1。
Note that exp(x)-1 can be approximated by x + x^2/2! + ... + x^n/n! and for any value
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);
}
?>