Function polars::functions::cov

pub fn cov<T>(
    a: &ChunkedArray<T>, 
    b: &ChunkedArray<T>
) -> Option<<T as PolarsPrimitiveType>::Native> where
    T: PolarsFloatType,
    <T as PolarsPrimitiveType>::Native: NativeType,
    <T as PolarsPrimitiveType>::Native: PartialOrd<<T as PolarsPrimitiveType>::Native>,
    <T as PolarsPrimitiveType>::Native: Float,
    <T as PolarsPrimitiveType>::Native: NumCast,
    <T as PolarsPrimitiveType>::Native: Simd,
    <<T as PolarsPrimitiveType>::Native as Simd>::Simd: Add<<<T as PolarsPrimitiveType>::Native as Simd>::Simd>,
    <<T as PolarsPrimitiveType>::Native as Simd>::Simd: Sum<<T as PolarsPrimitiveType>::Native>,
    <<T as PolarsPrimitiveType>::Native as Simd>::Simd: SimdOrd<<T as PolarsPrimitiveType>::Native>,
    <<<T as PolarsPrimitiveType>::Native as Simd>::Simd as Add<<<T as PolarsPrimitiveType>::Native as Simd>::Simd>>::Output == <<T as PolarsPrimitiveType>::Native as Simd>::Simd, 

Compute the covariance between two columns.