Function rosenbrock

pub fn rosenbrock<T>(x: &T, a: Scalar, b: Scalar) -> Scalar
where
    T: Tensor<Item = Scalar>,

Returns the Rosenbrock function.

f(\mathbf{x}) = \sum_{i=1}^{N-1} \left[\left(a - x_i\right)^2 + b\left(x_{i+1} - x_i^2\right)^2\right]