Function svd_centered 

pub fn svd_centered<T: SvdFloat, M: SparseMatDense<T>>(
    a: &M,
    rank: usize,
    seed: Option<u64>,
) -> Result<SvdRec<T>>

PCA: the rank largest singular triplets of the implicitly mean-centered matrix.

The centering is applied as a rank-1 correction inside each product, so the matrix is never densified.