# multiplicative inverse of 0.0

This page is part of the web mail archives of SRFI 77 from before July 7th, 2015. The new archives for SRFI 77 contain all messages, not just those from before July 7th, 2015.

``` | procedure: expt z1 z2
|
|     Returns z1 raised to the power z2. For nonzero z1
|
|     z1^z2 = e^(z2 log z1)
|
|     0^z is 1 if z = 0, and 0 if `(real-part z)' is positive.
|     Otherwise, this procedure reports a violation of an
|     implementation restriction or returns an unspecified number.

(expt x -1) is another way of writing (/ x);
(expt x -2) is (/ (expt x 2)); etc.
SRFI-77 specifies (/ 0.), but not (expt 0. -1).

SRFI-70's treatment of EXPT is consistent with `/' in this regard.
And this aspect was not controversial.

For inexact arguments not both zero
(define (expt z1 z2) (exp (* (if (zero? z1) (real-part z2) z2) (log z1))))

Why did SRFI-77 eschew SRFI-70's straightforward and safe
generalization of EXPT to (returning) -inf.0?

| (expt 5 3)                  ==>  125
| (expt 5 -3)                 ==>  1/125
| (expt 5 0)                  ==>  1
| (expt 0 5)                  ==>  0
| (expt 0 5+.0000312i)        ==>  0
| (expt 0 -5)                 ==>  unspecified
| (expt 0 -5+.0000312i)       ==>  unspecified
| (expt 0 0)                  ==>   [sic]

(expt 0 0) should return 1 (exact).