Function mul_frule 

pub fn mul_frule<S: ScalarAd>(x: S, y: S, dx: S, dy: S) -> (S, S)

Forward rule for mul.

Returns (primal, tangent).

Examples

use chainrules::mul_frule;

let (y, dy) = mul_frule(2.0_f64, 4.0_f64, 0.5_f64, 0.25_f64);
assert_eq!(y, 8.0_f64);
assert_eq!(dy, 2.5_f64);