Function powi_rrule 

pub fn powi_rrule<S: ScalarAd>(x: S, exponent: i32, cotangent: S) -> S

Reverse rule for powi with fixed integer exponent.

Examples

use chainrules::powi_rrule;

let dx = powi_rrule(2.0_f64, 4, 1.0);
assert_eq!(dx, 32.0);