log1p

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

log1p — 返回 log(1 + number)，甚至当 number 的值接近零也能计算出准确结果

说明

log1p(float $number): float

log1p() 返回 log(1 + number)，甚至当 number 的值接近零也能计算出准确结果。 log() might only return log(1) in this case due to lack of precision.

参数

number: 要处理的参数

返回值

log(1 + number)

更新日志

版本	说明
5.3.0	此函数在所有平台上均可用

参见

expm1() - 返回 exp(number) - 1，甚至当 number 的值接近零也能计算出准确结果
log() - 自然对数
log10() - 以 10 为底的对数

add a note

User Contributed Notes 1 note

down

Anonymous ¶

19 years ago


Note that the benefit of this function for small argument values is lost if PHP is compiled against a C library that that not have builtin support for the log1p() function.

In this case, log1p() will be compiled by using log() instead, and the precision of the result will be identical to log(1), i.e. it will always be 0 for small numbers.
Sample log1p(1.0e-20):
- returns 0.0 if log1p() is approximated by using log()
- returns something very near from 1.0e-20, if log1p() is supported by the underlying C library.

One way to support log1p() correctly on any platform, so that the magnitude of the expected result is respected:

function log1p($x) {
return ($x>-1.0e-8 && $x<1.0e-8) ? ($x - $x*$x/2) : log(1+$x);
}

If you want better precision, you may use a better limited development, for small positive or negative values of x:

log(1+x) = x - x^2/2 + x^3/3 - ... + (-1)^(n-1)*x^n/n + ...

(This serial sum converges only for values of x in [0 ... 1] inclusive, and the ^ operator in the above formula means the exponentiation operator, not the PHP xor operation)

Note that log1p() is undefined for arguments lower than or equal to -1, and that the implied base of the log function is the Neperian "e" constant.

add a note

官方地址：https://www.php.net/manual/en/function.log1p.php

有任何技术问题请点击这里网站运营推广招聘

IT PHP 编程语言 Linux 开发编程科技 Elasticsearch HTML/CSS/XML 网络 JAVA NoSQL 数据库面试 C/C++ Golang Git 算法操作系统正则表达式 Redis 互联网 MySql JavaScript 运维软件国际架构设计 Mac OS TCP/IP Excel Vim Windows Socket Oracle VR MongoDB Python 运营 MemCache 商业硬件电子娱乐设计 nginx 摄影游戏 WordPress HTTP 团建数码电器

php7 安装fileinfo扩展 preg_split — 通过一个正则表达式分隔字符串 php位值,解决 PHP 中 usort 在值相同时改变原始位置的问题 [PHP] inet_pton/inet_ntop IP地址转换函数 array_multisort() 多字段排序 PHPMailer设置utf8 PHPMailer字符集CharSet ADORecordSet对象 adodb手册 PHP 8.1 [鸟哥]PHP_INT_MIN 和 -9223372036854775808 opcache预加载 Composer的Packagist资源 mysql面试题 [鸟哥]PHP FFI详解 - 一种全新的PHP扩展方式 PHP7添加redis扩展 PHP mkdir()写出来的权限与mode值不符合 Packagist / Composer 中国全量镜像 PHP获取指定函数定义在哪个文件中及行号利用php soap实现web service PHPstorm 里面Terminal 不能使用 esc键吗退出编辑模式吗

略微加速

PHP官方手册 - 互联网笔记

log1p

说明

参数

返回值

更新日志

参见

User Contributed Notes 1 note