Math.log1p()
The Math.log1p()
static method returns the natural logarithm (base e) of 1 + x
, where x
is the argument. That is:
Try it
Syntax
js
Math.log1p(x)
Parameters
x
-
A number greater than or equal to -1.
Return value
Description
For very small values of x, adding 1 can reduce or eliminate precision. The double floats used in JS give you about 15 digits of precision. 1 + 1e-15 = 1.000000000000001, but 1 + 1e-16 = 1.000000000000000 and therefore exactly 1.0 in that arithmetic, because digits past 15 are rounded off.
When you calculate log(1 + x) where x is a small positive number, you should get an answer very close to x, because
. If you calculate Math.log(1 + 1.1111111111e-15)
, you should get an answer close to 1.1111111111e-15
. Instead, you will end up taking the logarithm of 1.00000000000000111022
(the roundoff is in binary, so sometimes it gets ugly), and get the answer 1.11022…e-15, with only 3 correct digits. If, instead, you calculate Math.log1p(1.1111111111e-15)
, you will get a much more accurate answer 1.1111111110999995e-15
, with 15 correct digits of precision (actually 16 in this case).
If the value of x
is less than -1, the return value is always NaN
.
Because log1p()
is a static method of Math
, you always use it as Math.log1p()
, rather than as a method of a Math
object you created (Math
is not a constructor).
Examples
Using Math.log1p()
js
Math.log1p(-2); // NaN
Math.log1p(-1); // -Infinity
Math.log1p(-0); // -0
Math.log1p(0); // 0
Math.log1p(1); // 0.6931471805599453
Math.log1p(Infinity); // Infinity
Specifications
Specification |
---|
ECMAScript Language Specification # sec-math.log1p |
Browser compatibility
BCD tables only load in the browser