Reference · Math

math.log

math.log(num, num=) -> float

What it does

The natural logarithm of a number, as a float, as Python's math.log. With a second argument, the logarithm to that base: math.log(8, 2) is 3.0. The number must be above zero, and the base above zero and not 1.

Examples

print(math.log(1), math.log(math.e), math.log(10))print(math.log(8, 2), math.log(100, 10), math.log(81, 3))

0.0 1.0 2.3025850929940463.0 2.0 4.0

Edge cases

• With a base the answer is ln(x) / ln(base), so it can miss by a digit: math.log(1000, 10) is 2.9999999999999996. math.log10 and math.log2 are exact for those bases.
• A base between 0 and 1 is allowed and gives a negative answer.
• A number between 0 and 1 gives a negative answer; the smallest positive float is still fine.
• inf gives inf, NaN gives NaN, and a base of inf gives 0.0.

print(math.log(1000, 10), math.log10(1000))print(math.log(8, 0.5))print(math.log(0.5), math.log(5e-324))print(math.log(math.inf), math.log(math.nan), math.log(8, math.inf))

2.9999999999999996 3.0-3.0-0.6931471805599453 -744.4400719213812inf NaN 0.0

Errors

Zero or a negative number is a runtime error (a domain error), not an error value: it stops the request, and ?? does not catch it, so test the value first when it can be zero. A base of 1, 0 or less is a domain error too, named as the base. A value that is not a number is a runtime error; a decimal is converted first with float.

print(math.log(0))

line 1: `math.log`: math domain error (0)

print(math.log(8, 1))

line 1: `math.log`: math domain error (base 1)

print(math.log(-1))

line 1: `math.log`: math domain error (-1)

Chaining

In a pipeline the number comes first, so x | math.log(2) is the logarithm of x to base 2. For a whole list, vec.log takes the natural logarithm of each item:

print(1024 | math.log(2))print([1, 10, 100] | map((x) => math.log(x, 10)), vec.log([1, math.e]))print(math.exp(2) | math.log)

10.0[0.0, 1.0, 2.0] [0.0, 1.0]2.0

See also

math.log2, math.log10, math.log1p, math.exp, vec.log

Edit this page on GitHub · every example's output was made by running it (tools/refcheck.mjs) · questions on Discord or r/quillo