Fix the ordering of derivatives the quadrature coefficients (CExA-project#1028)

* Fix the ordering of derivatives of the quadrature coefficients

* Increase tolerance

Author: tpadioleau

include/ddc/kernels/splines/spline_builder.hpp

@@ -730,10 +730,7 @@ void SplineBuilder<ExecSpace, MemorySpace, BSplines, InterpolationDDim, BcLower,
             // iterate only to deg as last bspline is 0
             for (std::size_t i = 0; i < s_nbc_xmin; ++i) {
                 for (std::size_t j = 0; j < bsplines_type::degree(); ++j) {
-                    m_matrix->set_element(
-                            i,
-                            j,
-                            DDC_MDSPAN_ACCESS_OP(derivs, j, s_nbc_xmin - i - 1 + s_odd));
+                    m_matrix->set_element(i, j, DDC_MDSPAN_ACCESS_OP(derivs, j, i + s_odd));
                 }
             }
         }
@@ -868,12 +865,12 @@ operator()(
                 KOKKOS_LAMBDA(
                         typename batch_domain_type<BatchedInterpolationDDom>::discrete_element_type
                                 j) {
-                    for (int i = s_nbc_xmin; i > 0; --i) {
-                        spline(ddc::DiscreteElement<bsplines_type>(s_nbc_xmin - i), j)
+                    for (int i = 0; i < s_nbc_xmin; ++i) {
+                        spline(ddc::DiscreteElement<bsplines_type>(i), j)
                                 = derivs_xmin_values(
-                                          ddc::DiscreteElement<deriv_type>(i + odd_proxy - 1),
+                                          ddc::DiscreteElement<deriv_type>(i + odd_proxy),
                                           j)
-                                  * ddc::detail::ipow(dx_proxy, i + odd_proxy - 1);
+                                  * ddc::detail::ipow(dx_proxy, i + odd_proxy);
                     }
                 });
     }
@@ -1087,8 +1084,7 @@ SplineBuilder<ExecSpace, MemorySpace, BSplines, InterpolationDDim, BcLower, BcUp
                 coefficients_derivs_xmin(i) *= ddc::detail::
                         ipow(dx_proxy,
                              static_cast<std::size_t>(get<bsplines_type>(
-                                     s_nbc_xmin + odd_proxy - 1
-                                     - (i - coefficients_derivs_xmin.domain().front()))));
+                                     (i - coefficients_derivs_xmin.domain().front()) + odd_proxy)));
             });
     ddc::parallel_for_each(
             exec_space(),
@@ -1097,15 +1093,14 @@ SplineBuilder<ExecSpace, MemorySpace, BSplines, InterpolationDDim, BcLower, BcUp
                 coefficients_derivs_xmax(i) *= ddc::detail::
                         ipow(dx_proxy,
                              static_cast<std::size_t>(get<bsplines_type>(
-                                     i - coefficients_derivs_xmax.domain().front() + odd_proxy)));
+                                     (i - coefficients_derivs_xmax.domain().front()) + odd_proxy)));
             });
 
     ddc::DiscreteElement<deriv_type> const first_deriv(s_odd);
     // Allocate Chunk on deriv_type and interpolation_discrete_dimension_type and copy quadrature coefficients into it
     ddc::Chunk coefficients_derivs_xmin_out(
-            ddc::DiscreteDomain<deriv_type>(
-                    first_deriv, // These indices are wrong the order should be reversed
-                    ddc::DiscreteVector<deriv_type>(s_nbc_xmin)),
+            ddc::DiscreteDomain<
+                    deriv_type>(first_deriv, ddc::DiscreteVector<deriv_type>(s_nbc_xmin)),
             ddc::KokkosAllocator<double, OutMemorySpace>());
     ddc::Chunk coefficients_out(
             interpolation_domain().take_first(

tests/splines/batched_2d_spline_builder.cpp

@@ -564,7 +564,7 @@ void TestBatched2dSpline()
                                 dx<I2>(ncells),
                                 s_degree,
                                 s_degree),
-                        1e-11 * max_norm_diff2));
+                        1e-10 * max_norm_diff2));
     EXPECT_LE(
             max_norm_error_diff12,
             std::
@@ -573,7 +573,7 @@ void TestBatched2dSpline()
                                 dx<I2>(ncells),
                                 s_degree,
                                 s_degree),
-                        1e-9 * max_norm_diff12));
+                        1e-8 * max_norm_diff12));
 }
 
 } // namespace anonymous_namespace_workaround_batched_2d_spline_builder_cpp

tests/splines/non_periodic_spline_builder.cpp

@@ -234,8 +234,7 @@ void TestNonPeriodicSplineBuilderTestIdentity()
             0.0,
             ddc::reducer::sum<double>(),
             KOKKOS_LAMBDA(ddc::DiscreteElement<ddc::Deriv<DimX>> const ix) {
-                return quadrature_coefficients_derivs_xmin(ix)
-                       * derivs_lhs(quadrature_coefficients_derivs_xmin.domain().back() - ix);
+                return quadrature_coefficients_derivs_xmin(ix) * derivs_lhs(ix);
             });
 #else
     double const quadrature_integral_derivs_xmin = 0.;