Function sphere

pub fn sphere<T>(param: &[T]) -> T
where
    T: Float + FromPrimitive + Sum,

Sphere test function.

Defined as

$$ f(x_1,\,x_2,\,\ldots,\,x_d) = \sum_{i=1}^d x_i^2 $$

where $x_i \in (-\infty, \infty)$ and $d > 0$.

The global minimum is at $f(x_1,\,x_2,\,\ldots,\,x_d) = f(0,\,0,\,\ldots,\,0) = 0$.