Create bsplines on a subset of a periodic domain

[EmilyBourne]

B-splines are created as periodic or non-periodic objects, but the periodicity is collected from the dimension. This means that it is not possible to create a B-spline on a sub-section of the domain without creating a new dimension. It would be simpler if the periodicity was a template parameter of the bsplines (which could be the periodicity of the dimension by default).

I.e. I would like to be able to do:

class DimPeriodic {
    static constexpr bool PERIODIC = true;
};

struct GridP : ddc::NonUniformPointSampling<DimPeriodic>
{
};

struct BSplinesP : UniformBSplines<DimPeriodic, 3>
{
};

void main() {
    ddc::Coordinate<DimPeriodic> p_min(0.0);
    ddc::Coordinate<DimPeriodic> p_max(2.0 * M_PI);
    std::size_t n_p(20);
    std::vector<ddc::Coordinate<DimPeriodic>> p_grid(n_p);
    p_grid[0] = p_min;
    for(std::size_t i(0); i < n_p-1; ++i)
        p_grid[i] = p_min + (p_max - p_min) / (n_p - 1);
    init_discrete_space<GridP>(p_grid);
    ddc::Coordinate<DimPeriodic> p_mid(M_PI);
    init_discrete_space<BSplinesP>(p_min, p_mid);
    ...
}

[tpadioleau]

I see, this is a new use case but it should be possible indeed.