exp()

(PHP 4, PHP 5, PHP 7)

计算e的指数

说明

返回e的$arg次方值。

用'e'作为自然对数的底 2.718282.

参数

要处理的参数

返回值

'e' raised to the power of$arg

范例

Example #1exp()例子

以上例程会输出：

1.6275E+005
298.87

参见

• log() 自然对数
• pow() 指数表达式

Note regarding the mathematical function exp(x):
To continue accuracy of the exponential function to an infinite amount of decimal places, one would use the power series definition for exp(x).
(in LaTeX form:)
e^x = \sum_{n=0}^{\infty} \frac{x^n}{n!}
So, to do that in PHP (using BC math): 

working version (checked) of below code is 

PHP does not have the following math function in any extensions:
frexp() - Extract Mantissa and Exponent of the Floating-Point Value
I've digged many C source codes, and found the simplest implementation as follows:

Array
(
  [0] => 0.552
  [1] => -4
)
Array
(
  [0] => 0.67309375
  [1] => 5
)
I have compared the results using a lot of floats against C's frexp function - they are the same.
Note that C and PHP uses different float precisions, for example "4619.3" gives:
C: 0.56387939453125, 13
PHP: 0.563879394531, 13
/Assuming default configurations./

Just a note about using the submitted codes below..
Their functions have an optional $precision parameter; however, it's not being used properly..
BCMath functions by default do not use decimal precision unless specified by BCScale($precision); or using the extra parameter in the used BC functions.
For example, a blank PHP file with their code.. executing BCExp('5.7'); returns "47" instead of the correct answer of "298.86740096706..."
So for optimum accuracy, I'd suggest setting BCScale to a healthy length before running their codes.

Which is the inverse of log(float $arg, e)

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