Function rfftn_optimized 

pub fn rfftn_optimized<T, D>(
    x: &ArrayView<'_, T, D>,
    _shape: Option<Vec<usize>>,
    axes: Option<Vec<usize>>,
) -> FFTResult<Array<Complex64, D>>
where
    T: NumCast + Copy + Send + Sync,
    D: Dimension,

Optimized real-to-complex N-dimensional FFT