integrate.hpp

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// Copyright (c) 2010-2026, Lawrence Livermore National Security, LLC. Produced
// at the Lawrence Livermore National Laboratory. All Rights reserved. See files
// LICENSE and NOTICE for details. LLNL-CODE-806117.
//
// This file is part of the MFEM library. For more information and source code
// availability visit https://mfem.org.
//
// MFEM is free software; you can redistribute it and/or modify it under the
// terms of the BSD-3 license. We welcome feedback and contributions, see file
// CONTRIBUTING.md for details.
#pragma once
 
#include "util.hpp"
 
namespace mfem::future
{
 
template <typename output_t>
MFEM_HOST_DEVICE
void map_quadrature_data_to_fields_impl(
   DeviceTensor<2, real_t> &y,
   const DeviceTensor<3, real_t> &f,
   const output_t &output,
   const DofToQuadMap &dtq)
{
   [[maybe_unused]] auto B = dtq.B;
   [[maybe_unused]] auto G = dtq.G;
 
   // assuming the quadrature point residual has to "play nice with
   // the test function"
   if constexpr (is_value_fop<std::decay_t<output_t>>::value)
   {
      const auto [num_qp, cdim, num_dof] = B.GetShape();
      const int vdim = output.vdim > 0 ? output.vdim : cdim ;
      for (int dof = 0; dof < num_dof; dof++)
      {
         for (int vd = 0; vd < vdim; vd++)
         {
            real_t acc = 0.0;
            for (int qp = 0; qp < num_qp; qp++)
            {
               acc += B(qp, 0, dof) * f(vd, 0, qp);
            }
            y(dof, vd) += acc;
         }
      }
   }
   else if constexpr (
      is_gradient_fop<std::decay_t<output_t>>::value)
   {
      const auto [num_qp, dim, num_dof] = G.GetShape();
      const int vdim = output.vdim;
      for (int dof = 0; dof < num_dof; dof++)
      {
         for (int vd = 0; vd < vdim; vd++)
         {
            real_t acc = 0.0;
            for (int d = 0; d < dim; d++)
            {
               for (int qp = 0; qp < num_qp; qp++)
               {
                  acc += G(qp, d, dof) * f(vd, d, qp);
               }
            }
            y(dof, vd) += acc;
         }
      }
   }
   else if constexpr (is_sum_fop<std::decay_t<output_t>>::value)
   {
      // This is the "integral over all quadrature points type" applying
      // B = 1 s.t. B^T * C \in R^1.
      const auto [num_qp, unused, unused1] = B.GetShape();
      auto cc = Reshape(&f(0, 0, 0), num_qp);
      for (int i = 0; i < num_qp; i++)
      {
         y(0, 0) += cc(i);
      }
   }
   else if constexpr (is_identity_fop<std::decay_t<output_t>>::value)
   {
      const auto [num_qp, unused, num_dof] = B.GetShape();
      const auto vdim = output.vdim;
      auto cc = Reshape(&f(0, 0, 0), num_qp * vdim);
      auto yy = Reshape(&y(0, 0), num_qp * vdim);
      for (int i = 0; i < num_qp * vdim; i++)
      {
         yy(i) = cc(i);
      }
   }
   else
   {
      MFEM_ABORT_KERNEL("quadrature data mapping to field is not implemented"
                        " for this field descriptor");
   }
}
 
template <typename output_t>
MFEM_HOST_DEVICE
void map_quadrature_data_to_fields_tensor_impl_1d(
   DeviceTensor<2, real_t> &y,
   const DeviceTensor<3, real_t> &f,
   const output_t &output,
   const DofToQuadMap &dtq,
   std::array<DeviceTensor<1>, 6> &scratch_mem)
{
   [[maybe_unused]] auto B = dtq.B;
   [[maybe_unused]] auto G = dtq.G;
 
   if constexpr (is_value_fop<std::decay_t<output_t>>::value)
   {
      const auto [q1d, unused, d1d] = B.GetShape();
      const int vdim = output.vdim;
      const int test_dim = output.size_on_qp / vdim;
 
      auto fqp = Reshape(&f(0, 0, 0), vdim, test_dim, q1d);
      auto yd = Reshape(&y(0, 0), d1d, vdim);
 
      for (int vd = 0; vd < vdim; vd++)
      {
         MFEM_FOREACH_THREAD(dx, x, d1d)
         {
            real_t acc = 0.0;
            for (int qx = 0; qx < q1d; qx++)
            {
               acc += fqp(vd, 0, qx) * B(qx, 0, dx);
            }
            yd(dx, vd) = acc;
         }
      }
      MFEM_SYNC_THREAD;
   }
   else if constexpr (is_gradient_fop<std::decay_t<output_t>>::value)
   {
      const auto [q1d, unused, d1d] = G.GetShape();
      const int vdim = output.vdim;
      const int test_dim = output.size_on_qp / vdim;
      auto fqp = Reshape(&f(0, 0, 0), vdim, test_dim, q1d);
      auto yd = Reshape(&y(0, 0), d1d, vdim);
 
      for (int vd = 0; vd < vdim; vd++)
      {
         MFEM_FOREACH_THREAD(dx, x, d1d)
         {
            real_t acc = 0.0;
            for (int qx = 0; qx < q1d; qx++)
            {
               acc += fqp(vd, 0, qx) * G(qx, 0, dx);
            }
            yd(dx, vd) = acc;
         }
      }
      MFEM_SYNC_THREAD;
   }
   else if constexpr (is_identity_fop<std::decay_t<output_t>>::value)
   {
      const auto [q1d, unused, d1d] = B.GetShape();
      auto fqp = Reshape(&f(0, 0, 0), output.size_on_qp, q1d);
      auto yqp = Reshape(&y(0, 0), output.size_on_qp, q1d);
 
      for (int sq = 0; sq < output.size_on_qp; sq++)
      {
         MFEM_FOREACH_THREAD(qx, x, q1d)
         {
            yqp(sq, qx) = fqp(sq, qx);
         }
         MFEM_SYNC_THREAD;
      }
   }
   else
   {
      MFEM_ABORT_KERNEL("quadrature data mapping to field is not implemented"
                        "for this field descriptor with sum factorization on"
                        " tensor product elements");
   }
}
 
template <typename output_t>
MFEM_HOST_DEVICE
void map_quadrature_data_to_fields_tensor_impl_2d(
   DeviceTensor<2, real_t> &y,
   const DeviceTensor<3, real_t> &f,
   const output_t &output,
   const DofToQuadMap &dtq,
   std::array<DeviceTensor<1>, 6> &scratch_mem)
{
   [[maybe_unused]] auto B = dtq.B;
   [[maybe_unused]] auto G = dtq.G;
 
   if constexpr (is_value_fop<std::decay_t<output_t>>::value)
   {
      const auto [q1d, unused, d1d] = B.GetShape();
      const int vdim = output.vdim;
      const int test_dim = output.size_on_qp / vdim;
 
      auto fqp = Reshape(&f(0, 0, 0), vdim, test_dim, q1d, q1d);
      auto yd = Reshape(&y(0, 0), d1d, d1d, vdim);
 
      auto s0 = Reshape(&scratch_mem[0](0), q1d, d1d);
 
      for (int vd = 0; vd < vdim; vd++)
      {
         MFEM_FOREACH_THREAD(qy, y, q1d)
         {
            MFEM_FOREACH_THREAD(dx, x, d1d)
            {
               real_t acc = 0.0;
               for (int qx = 0; qx < q1d; qx++)
               {
                  acc += fqp(vd, 0, qx, qy) * B(qx, 0, dx);
               }
               s0(qy, dx) = acc;
            }
         }
         MFEM_SYNC_THREAD;
 
         MFEM_FOREACH_THREAD(dy, y, d1d)
         {
            MFEM_FOREACH_THREAD(dx, x, d1d)
            {
               real_t acc = 0.0;
               for (int qy = 0; qy < q1d; qy++)
               {
                  acc += s0(qy, dx) * B(qy, 0, dy);
               }
               yd(dx, dy, vd) += acc;
            }
         }
         MFEM_SYNC_THREAD;
      }
   }
   else if constexpr (is_gradient_fop<std::decay_t<output_t>>::value)
   {
      const auto [q1d, unused, d1d] = G.GetShape();
      const int vdim = output.vdim;
      const int test_dim = output.size_on_qp / vdim;
      auto fqp = Reshape(&f(0, 0, 0), vdim, test_dim, q1d, q1d);
      auto yd = Reshape(&y(0, 0), d1d, d1d, vdim);
 
      auto s0 = Reshape(&scratch_mem[0](0), q1d, d1d);
      auto s1 = Reshape(&scratch_mem[1](0), q1d, d1d);
 
      for (int vd = 0; vd < vdim; vd++)
      {
         MFEM_FOREACH_THREAD(qy, y, q1d)
         {
            MFEM_FOREACH_THREAD(dx, x, d1d)
            {
               real_t uv[2] = {0.0, 0.0};
               for (int qx = 0; qx < q1d; qx++)
               {
                  uv[0] += fqp(vd, 0, qx, qy) * G(qx, 0, dx);
                  uv[1] += fqp(vd, 1, qx, qy) * B(qx, 0, dx);
               }
               s0(qy, dx) = uv[0];
               s1(qy, dx) = uv[1];
            }
         }
         MFEM_SYNC_THREAD;
 
         MFEM_FOREACH_THREAD(dy, y, d1d)
         {
            MFEM_FOREACH_THREAD(dx, x, d1d)
            {
               real_t uv[2] = {0.0, 0.0};
               for (int qy = 0; qy < q1d; qy++)
               {
                  uv[0] += s0(qy, dx) * B(qy, 0, dy);
                  uv[1] += s1(qy, dx) * G(qy, 0, dy);
               }
               yd(dx, dy, vd) += uv[0] + uv[1];
            }
         }
         MFEM_SYNC_THREAD;
      }
   }
   else if constexpr (is_identity_fop<std::decay_t<output_t>>::value)
   {
      const auto [q1d, unused, d1d] = B.GetShape();
 
      // // TODO: Check if this is the right fix for all cases
      // auto fqp = Reshape(&f(0, 0, 0), output.size_on_qp, q1d);
      // auto yqp = Reshape(&y(0, 0), output.size_on_qp, q1d);
      // for (int sq = 0; sq < output.size_on_qp; sq++)
      // {
      //    MFEM_FOREACH_THREAD(qx, x, q1d)
      //    {
      //       yqp(sq, qx) = fqp(sq, qx);
      //    }
      //    MFEM_SYNC_THREAD;
      // }
 
      auto fqp = Reshape(&f(0, 0, 0), output.size_on_qp, q1d, q1d);
      auto yqp = Reshape(&y(0, 0), output.size_on_qp, q1d, q1d);
 
      for (int sq = 0; sq < output.size_on_qp; sq++)
      {
         MFEM_FOREACH_THREAD(qx, x, q1d)
         {
            MFEM_FOREACH_THREAD(qy, y, q1d)
            {
               yqp(sq, qx, qy) = fqp(sq, qx, qy);
            }
         }
         MFEM_SYNC_THREAD;
      }
   }
   else
   {
      MFEM_ABORT_KERNEL("quadrature data mapping to field is not implemented"
                        " for this field descriptor with sum factorization on"
                        " tensor product elements");
   }
}
 
template <typename output_t>
MFEM_HOST_DEVICE
void map_quadrature_data_to_fields_tensor_impl_3d(
   DeviceTensor<2, real_t> &y,
   const DeviceTensor<3, real_t> &f,
   const output_t &output,
   const DofToQuadMap &dtq,
   std::array<DeviceTensor<1>, 6> &scratch_mem)
{
   [[maybe_unused]] auto B = dtq.B;
   [[maybe_unused]] auto G = dtq.G;
 
   if constexpr (is_value_fop<std::decay_t<output_t>>::value)
   {
      const auto [q1d, unused, d1d] = B.GetShape();
      const int vdim = output.vdim;
      const int test_dim = output.size_on_qp / vdim;
 
      auto fqp = Reshape(&f(0, 0, 0), vdim, test_dim, q1d, q1d, q1d);
      auto yd = Reshape(&y(0, 0), d1d, d1d, d1d, vdim);
 
      auto s0 = Reshape(&scratch_mem[0](0), q1d, q1d, d1d);
      auto s1 = Reshape(&scratch_mem[1](0), q1d, d1d, d1d);
 
      for (int vd = 0; vd < vdim; vd++)
      {
         MFEM_FOREACH_THREAD(qy, y, q1d)
         {
            MFEM_FOREACH_THREAD(dx, x, d1d)
            {
               MFEM_FOREACH_THREAD(qz, z, q1d)
               {
                  real_t acc = 0.0;
                  for (int qx = 0; qx < q1d; qx++)
                  {
                     acc += fqp(vd, 0, qx, qy, qz) * B(qx, 0, dx);
                  }
                  s0(qz, qy, dx) = acc;
               }
            }
         }
         MFEM_SYNC_THREAD;
 
         MFEM_FOREACH_THREAD(dy, y, d1d)
         {
            MFEM_FOREACH_THREAD(dx, x, d1d)
            {
               MFEM_FOREACH_THREAD(qz, z, q1d)
               {
                  real_t acc = 0.0;
                  for (int qy = 0; qy < q1d; qy++)
                  {
                     acc += s0(qz, qy, dx) * B(qy, 0, dy);
                  }
                  s1(qz, dy, dx) = acc;
               }
            }
         }
         MFEM_SYNC_THREAD;
 
 
         MFEM_FOREACH_THREAD(dy, y, d1d)
         {
            MFEM_FOREACH_THREAD(dx, x, d1d)
            {
               MFEM_FOREACH_THREAD(dz, z, d1d)
               {
                  real_t acc = 0.0;
                  for (int qz = 0; qz < q1d; qz++)
                  {
                     acc += s1(qz, dy, dx) * B(qz, 0, dz);
                  }
                  yd(dx, dy, dz, vd) += acc;
               }
            }
         }
         MFEM_SYNC_THREAD;
      }
   }
   else if constexpr (is_gradient_fop<std::decay_t<output_t>>::value)
   {
      const auto [q1d, unused, d1d] = G.GetShape();
      const int vdim = output.vdim;
      const int test_dim = output.size_on_qp / vdim;
      auto fqp = Reshape(&f(0, 0, 0), vdim, test_dim, q1d, q1d, q1d);
      auto yd = Reshape(&y(0, 0), d1d, d1d, d1d, vdim);
 
      auto s0 = Reshape(&scratch_mem[0](0), q1d, q1d, d1d);
      auto s1 = Reshape(&scratch_mem[1](0), q1d, q1d, d1d);
      auto s2 = Reshape(&scratch_mem[2](0), q1d, q1d, d1d);
      auto s3 = Reshape(&scratch_mem[3](0), q1d, d1d, d1d);
      auto s4 = Reshape(&scratch_mem[4](0), q1d, d1d, d1d);
      auto s5 = Reshape(&scratch_mem[5](0), q1d, d1d, d1d);
 
      for (int vd = 0; vd < vdim; vd++)
      {
         MFEM_FOREACH_THREAD(qz, z, q1d)
         {
            MFEM_FOREACH_THREAD(qy, y, q1d)
            {
               MFEM_FOREACH_THREAD(dx, x, d1d)
               {
                  real_t uvw[3] = {0.0, 0.0, 0.0};
                  for (int qx = 0; qx < q1d; qx++)
                  {
                     uvw[0] += fqp(vd, 0, qx, qy, qz) * G(qx, 0, dx);
                     uvw[1] += fqp(vd, 1, qx, qy, qz) * B(qx, 0, dx);
                     uvw[2] += fqp(vd, 2, qx, qy, qz) * B(qx, 0, dx);
                  }
                  s0(qz, qy, dx) = uvw[0];
                  s1(qz, qy, dx) = uvw[1];
                  s2(qz, qy, dx) = uvw[2];
               }
            }
         }
         MFEM_SYNC_THREAD;
 
         MFEM_FOREACH_THREAD(qz, z, q1d)
         {
            MFEM_FOREACH_THREAD(dy, y, d1d)
            {
               MFEM_FOREACH_THREAD(dx, x, d1d)
               {
                  real_t uvw[3] = {0.0, 0.0, 0.0};
                  for (int qy = 0; qy < q1d; qy++)
                  {
                     uvw[0] += s0(qz, qy, dx) * B(qy, 0, dy);
                     uvw[1] += s1(qz, qy, dx) * G(qy, 0, dy);
                     uvw[2] += s2(qz, qy, dx) * B(qy, 0, dy);
                  }
                  s3(qz, dy, dx) = uvw[0];
                  s4(qz, dy, dx) = uvw[1];
                  s5(qz, dy, dx) = uvw[2];
               }
            }
         }
         MFEM_SYNC_THREAD;
 
         MFEM_FOREACH_THREAD(dz, z, d1d)
         {
            MFEM_FOREACH_THREAD(dy, y, d1d)
            {
               MFEM_FOREACH_THREAD(dx, x, d1d)
               {
                  real_t uvw[3] = {0.0, 0.0, 0.0};
                  for (int qz = 0; qz < q1d; qz++)
                  {
                     uvw[0] += s3(qz, dy, dx) * B(qz, 0, dz);
                     uvw[1] += s4(qz, dy, dx) * B(qz, 0, dz);
                     uvw[2] += s5(qz, dy, dx) * G(qz, 0, dz);
                  }
                  yd(dx, dy, dz, vd) += uvw[0] + uvw[1] + uvw[2];
               }
            }
         }
         MFEM_SYNC_THREAD;
      }
   }
   else if constexpr (is_identity_fop<std::decay_t<output_t>>::value)
   {
      const auto [q1d, unused, d1d] = B.GetShape();
      auto fqp = Reshape(&f(0, 0, 0), output.size_on_qp, q1d, q1d, q1d);
      auto yqp = Reshape(&y(0, 0), output.size_on_qp, q1d, q1d, q1d);
 
      for (int sq = 0; sq < output.size_on_qp; sq++)
      {
         MFEM_FOREACH_THREAD(qx, x, q1d)
         {
            MFEM_FOREACH_THREAD(qy, y, q1d)
            {
               MFEM_FOREACH_THREAD(qz, z, q1d)
               {
                  yqp(sq, qx, qy, qz) = fqp(sq, qx, qy, qz);
               }
            }
         }
         MFEM_SYNC_THREAD;
      }
   }
   else
   {
      MFEM_ABORT_KERNEL("quadrature data mapping to field is not implemented"
                        " for this field descriptor with sum factorization on"
                        " tensor product elements");
   }
}
 
template <typename output_t>
MFEM_HOST_DEVICE
void map_quadrature_data_to_fields(
   DeviceTensor<2, real_t> &y,
   const DeviceTensor<3, real_t> &f,
   const output_t &output,
   const DofToQuadMap &dtq,
   std::array<DeviceTensor<1>, 6> &scratch_mem,
   const int &dimension,
   const bool &use_sum_factorization)
{
   if (use_sum_factorization)
   {
      if (dimension == 1)
      {
         map_quadrature_data_to_fields_tensor_impl_1d(y, f, output, dtq, scratch_mem);
      }
      else if (dimension == 2)
      {
         map_quadrature_data_to_fields_tensor_impl_2d(y, f, output, dtq, scratch_mem);
      }
      else if (dimension == 3)
      {
         map_quadrature_data_to_fields_tensor_impl_3d(y, f, output, dtq, scratch_mem);
      }
      else { MFEM_ABORT_KERNEL("dimension not supported"); }
   }
   else
   {
      map_quadrature_data_to_fields_impl(y, f, output, dtq);
   }
}
 
} // namespace mfem::future