Function math::stats::variance

pub fn variance<'a, T: Clone + Iterator<Item = &'a A>, A>(
    element_iterator: T, 
    ddof: usize
) -> f64 where
    A: Copy + ToPrimitive + 'a,
    &'a A: Deref, 

ddof stands for delta degress of freedom, and the sum of squares will be divided by count - ddof, where count is the number of elements for population variance, set ddof to 0 for sample variance, set ddof to 1