Function scale 

pub fn scale<T>(backend: ComputeBackend, a: &Field<T>, s: f64) -> Field<T>
where
    T: Copy + Send + Sync + Mul<f64, Output = T>,

Uniform scaling c[i] = a[i] * s, returning a new field.

Used for under-relaxation (s = alpha, dimensionless), for 1/dt weighting (s in s^-1), and for negation (s = -1.0).

Units: the result carries [a] * [s]; this layer treats s as a bare number and cannot check it. Bit-identical to the serial std::ops::Mul<f64> impl on Field.