⍟ — Natural log / Logarithm

Function. Keys: Alt-o 8. Ranks: 0 monadic, 0 0 dyadic

⍟Y: ln Y. Pervasive.

⍟1                ⍝ 0

X⍟Y: logX Y. Pervasive.

2⍟8               ⍝ 3
10⍟100            ⍝ 2

Uses complex logarithms where needed. ⍟0 is ¯∞, as IEEE 754 gives it. With base 1, the result is an infinity or NaN.

Inverse

⍟⁻¹ is *. With the right argument fixed, (⍟↢X)⁻¹Y is X*÷Y.

2⍟⁻¹3      ⍝ 8
(⍟↢8)⁻¹3   ⍝ 2