Function simplex_exp_map 

pub fn simplex_exp_map(
    tangent: ArrayView2<'_, f64>,
    base: ArrayView1<'_, f64>,
    coord: SimplexCoord,
    reference: isize,
) -> Result<Array2<f64>, String>

Riemannian exp map from tangent coordinates back to the simplex at base, inverting simplex_log_map for the matching coordinate system.