Function derivatives 

pub fn derivatives(
    wave: Family,
    k: Complex,
    lattice: &BlochLattice,
    shift: [f64; 3],
    eta: Complex,
) -> Result<Derivatives>

Differentiate an Ewald sum using analytic integral identities and Cartesian polynomials.

Derivatives of 1D spherical sums carry rounding bounds of their own, from the Kambe orders one above and one below the value’s. Each derivative that loses more than 1e-12 of its scale comes from the spectral series (see the module docs). Where only derivatives switch, the value stays the Ewald sum’s, whose bound is then within 1e-12 max(|S|, 1).

Errors

As sum.