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expm1
Returns exp(number) - 1, computed in a way that is accurate even
when the value of number is close to zero
(PHP 4 >= 4.0.7, PHP 5)
Warning:
This function is EXPERIMENTAL. The behaviour of this function, the name of this function, and anything else documented about this function may change without notice in a future release of PHP. Use this function at your own risk. expm1() returns the equivalent to 'exp(arg) - 1' computed in a way that is accurate even if the value of arg is near zero, a case where 'exp (arg) - 1' would be inaccurate due to subtraction of two numbers that are nearly equal.
Note:
This function is not implemented on Windows platforms. Code Examples / Notes » expm1hagen
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: function expm1($x) { return ($x>-1.0e-6 && $x<1.0e-6) ? ($x + $x*$x/2) : (exp($x)-1); } |