BiLinearFormsIntegrators.hpp

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/** \file BiLinearFormsIntegrators.hpp
  * \brief Bilinear forms integrators
  * \ingroup mofem_form
 
  \todo SSome operators could be optimised. To do that, we need to write tests
  and use Valgrind to profile code, shaking cache misses. For example, some
  operators should have iteration first over columns, then rows. ome operators.
  Since those operators are used in many problems, an implementation must be
  efficient.
 
*/
 
#ifndef __BILINEAR_FORMS_INTEGRATORS_HPP__
#define __BILINEAR_FORMS_INTEGRATORS_HPP__
 
namespace MoFEM {
 
template <int BASE_DIM, int FIELD_DIM, int SPACE_DIM, IntegrationType I,
          typename OpBase>
struct OpGradGradImpl {};
 
template <int SPACE_DIM, typename OpBase>
struct OpGradGradImpl<1, 1, SPACE_DIM, GAUSS, OpBase> : public OpBase {
  FTensor::Index<'i', SPACE_DIM> i; ///< summit Index
  OpGradGradImpl(const std::string row_field_name,
                 const std::string col_field_name,
                 ScalarFun beta = scalar_fun_one,
                 boost::shared_ptr<Range> ents_ptr = nullptr)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL, ents_ptr),
        betaCoeff(beta) {
    if (row_field_name == col_field_name)
      this->sYmm = true;
  }
 
protected:
  ScalarFun betaCoeff;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int FIELD_DIM, int SPACE_DIM, typename OpBase>
struct OpGradGradImpl<1, FIELD_DIM, SPACE_DIM, GAUSS, OpBase> : public OpBase {
  FTensor::Index<'i', SPACE_DIM> i; ///< summit Index
  OpGradGradImpl(const std::string row_field_name,
                 const std::string col_field_name,
                 ScalarFun beta = scalar_fun_one,
                 boost::shared_ptr<Range> ents_ptr = nullptr)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL, ents_ptr),
        betaCoeff(beta) {
    if (row_field_name == col_field_name)
      this->sYmm = true;
  }
 
protected:
  ScalarFun betaCoeff;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int BASE_DIM, int FIELD_DIM, IntegrationType I, typename OpBase>
struct OpMassImpl {};
 
template <typename OpBase>
struct OpMassImpl<1, 1, GAUSS, OpBase> : public OpBase {
 
  OpMassImpl(
      const std::string row_field_name, const std::string col_field_name,
      ScalarFun beta = [](double, double, double) constexpr { return 1; },
      boost::shared_ptr<Range> ents_ptr = nullptr)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL, ents_ptr),
        betaCoeff(beta) {
    if (row_field_name == col_field_name)
      this->sYmm = true;
  }
 
protected:
  ScalarFun betaCoeff;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int FIELD_DIM, typename OpBase>
struct OpMassImpl<1, FIELD_DIM, GAUSS, OpBase>
    : public OpMassImpl<1, 1, GAUSS, OpBase> {
  using OpMassImpl<1, 1, GAUSS, OpBase>::OpMassImpl;
 
protected:
  using OpMassImpl<1, 1, GAUSS, OpBase>::betaCoeff;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int FIELD_DIM, typename OpBase>
struct OpMassImpl<3, FIELD_DIM, GAUSS, OpBase> : public OpBase {
 
  OpMassImpl(const std::string row_field_name, const std::string col_field_name,
             ScalarFun beta = scalar_fun_one,
             boost::shared_ptr<Range> ents_ptr = nullptr)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL, ents_ptr),
        betaCoeff(beta) {
    if (row_field_name == col_field_name)
      this->sYmm = true;
  }
 
protected:
  ScalarFun betaCoeff;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <typename OpBase>
struct OpMassImpl<3, 4, GAUSS, OpBase> : public OpBase {
  OpMassImpl(const std::string row_field_name, const std::string col_field_name,
             ScalarFun beta = scalar_fun_one,
             boost::shared_ptr<Range> ents_ptr = nullptr)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL, ents_ptr),
        betaCoeff(beta) {
    if (row_field_name == col_field_name)
      this->sYmm = true;
  }
 
protected:
  ScalarFun betaCoeff;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <typename OpBase>
struct OpMassImpl<3, 9, GAUSS, OpBase> : public OpBase {
  OpMassImpl(const std::string row_field_name, const std::string col_field_name,
             ScalarFun beta = scalar_fun_one,
             boost::shared_ptr<Range> ents_ptr = nullptr)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL, ents_ptr),
        betaCoeff(beta) {
    if (row_field_name == col_field_name)
      this->sYmm = true;
  }
 
protected:
  ScalarFun betaCoeff;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int BASE_DIM, int FIELD_DIM, int SPACE_DIM, int S, IntegrationType I,
          typename OpBase>
struct OpGradSymTensorGradImpl {};
 
template <int SPACE_DIM, int S, typename OpBase>
struct OpGradSymTensorGradImpl<1, SPACE_DIM, SPACE_DIM, S, GAUSS, OpBase>
    : public OpBase {
  FTensor::Index<'i', SPACE_DIM> i; ///< summit Index
  OpGradSymTensorGradImpl(const std::string row_field_name,
                          const std::string col_field_name,
                          boost::shared_ptr<MatrixDouble> mat_D,
                          boost::shared_ptr<Range> ents_ptr = nullptr,
                          ScalarFun beta = scalar_fun_one)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL, ents_ptr),
        matD(mat_D), betaCoeff(beta) {
    if (row_field_name == col_field_name)
      this->sYmm = true;
  }
 
protected:
  boost::shared_ptr<MatrixDouble> matD;
  ScalarFun betaCoeff;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int BASE_DIM, int FIELD_DIM, int SPACE_DIM, int S, IntegrationType I,
          typename OpBase>
struct OpGradTensorGradImpl {};
 
template <int SPACE_DIM, int S, typename OpBase>
struct OpGradTensorGradImpl<1, SPACE_DIM, SPACE_DIM, S, GAUSS, OpBase>
    : public OpBase {
  FTensor::Index<'i', SPACE_DIM> i; ///< summit Index
  OpGradTensorGradImpl(const std::string row_field_name,
                       const std::string col_field_name,
                       boost::shared_ptr<MatrixDouble> mat_D,
                       ScalarFun beta = scalar_fun_one)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL), matD(mat_D),
        betaCoeff(beta) {}
 
protected:
  boost::shared_ptr<MatrixDouble> matD;
  ScalarFun betaCoeff;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int BASE_DIM, int FIELD_DIM, int SPACE_DIM, int S, IntegrationType I,
          typename OpBase>
struct OpGradGradSymTensorGradGradImpl {};
 
template <int SPACE_DIM, int S, typename OpBase>
struct OpGradGradSymTensorGradGradImpl<1, 1, SPACE_DIM, S, GAUSS, OpBase>
    : public OpBase {
  FTensor::Index<'i', SPACE_DIM> i; ///< summit Index
  OpGradGradSymTensorGradGradImpl(const std::string row_field_name,
                                  const std::string col_field_name,
                                  boost::shared_ptr<MatrixDouble> mat_D,
                                  boost::shared_ptr<Range> ents_ptr = nullptr)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL, ents_ptr),
        matD(mat_D) {
    if (row_field_name == col_field_name)
      this->sYmm = true;
  }
 
protected:
  boost::shared_ptr<MatrixDouble> matD;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int SPACE_DIM, IntegrationType I, typename OpBase>
struct OpMixDivTimesScalarImpl {};
 
template <int SPACE_DIM, typename OpBase>
struct OpMixDivTimesScalarImpl<SPACE_DIM, GAUSS, OpBase> : public OpBase {
  OpMixDivTimesScalarImpl(const std::string row_field_name,
                          const std::string col_field_name,
                          ConstantFun alpha_fun,
                          const bool assemble_transpose = false,
                          const bool only_transpose = false)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL),
        alphaConstant(alpha_fun) {
    this->assembleTranspose = assemble_transpose;
    this->onlyTranspose = only_transpose;
  }
 
protected:
  FTensor::Index<'i', SPACE_DIM> i; ///< summit Index
  ConstantFun alphaConstant;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int SPACE_DIM, IntegrationType I, typename OpBase,
          CoordinateTypes CoordSys>
struct OpMixDivTimesVecImpl {};
 
template <int SPACE_DIM, typename OpBase, CoordinateTypes CoordSys>
struct OpMixDivTimesVecImpl<SPACE_DIM, GAUSS, OpBase, CoordSys>
    : public OpBase {
 
  OpMixDivTimesVecImpl(const std::string row_field_name,
                       const std::string col_field_name, ConstantFun alpha_fun,
                       const bool assemble_transpose,
                       const bool only_transpose = false)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL),
        alphaConstant(alpha_fun) {
    this->assembleTranspose = assemble_transpose;
    this->onlyTranspose = only_transpose;
  }
 
  OpMixDivTimesVecImpl(const std::string row_field_name,
                       const std::string col_field_name, ConstantFun alpha_fun,
                       ScalarFun beta_fun, const bool assemble_transpose,
                       const bool only_transpose = false)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL),
        alphaConstant(alpha_fun), betaCoeff(beta_fun) {
    this->assembleTranspose = assemble_transpose;
    this->onlyTranspose = only_transpose;
  }
 
protected:
  FTensor::Index<'i', SPACE_DIM> i; ///< summit Index
 
  ConstantFun alphaConstant = []() constexpr { return 1; };
  ScalarFun betaCoeff = [](double, double, double) constexpr { return 1; };
 
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int SPACE_DIM, IntegrationType I, typename OpBase,
          CoordinateTypes COORDINATE_SYSTEM>
struct OpMixScalarTimesDivImpl {};
 
template <int SPACE_DIM, typename OpBase, CoordinateTypes COORDINATE_SYSTEM>
struct OpMixScalarTimesDivImpl<SPACE_DIM, GAUSS, OpBase, COORDINATE_SYSTEM>
    : public OpBase {
  OpMixScalarTimesDivImpl(
      const std::string row_field_name, const std::string col_field_name,
      ScalarFun alpha_fun = [](double, double, double) constexpr { return 1; },
      const bool assemble_transpose = false, const bool only_transpose = false)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL),
        alphaConstant(alpha_fun) {
    this->assembleTranspose = assemble_transpose;
    this->onlyTranspose = only_transpose;
    this->sYmm = false;
  }
 
protected:
  FTensor::Index<'i', SPACE_DIM> i; ///< summit Index
  ScalarFun alphaConstant;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int BASE_DIM, int FIELD_DIM, int SPACE_DIM, IntegrationType I,
          typename OpBase>
struct OpMixVectorTimesGradImpl;
 
template <int SPACE_DIM, typename OpBase>
struct OpMixVectorTimesGradImpl<3, SPACE_DIM, SPACE_DIM, GAUSS, OpBase>
    : public OpBase {
  OpMixVectorTimesGradImpl(const std::string row_field_name,
                           const std::string col_field_name,
                           ConstantFun alpha_fun,
                           const bool assemble_transpose = false,
                           const bool only_transpose = false)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL),
        alphaConstant(alpha_fun) {
    this->assembleTranspose = assemble_transpose;
    this->onlyTranspose = only_transpose;
  }
 
protected:
  FTensor::Index<'i', SPACE_DIM> i; ///< summit Index
  ConstantFun alphaConstant;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int SPACE_DIM, typename OpBase>
struct OpMixVectorTimesGradImpl<1, SPACE_DIM, SPACE_DIM, GAUSS, OpBase>
    : public OpBase {
  OpMixVectorTimesGradImpl(const std::string row_field_name,
                           const std::string col_field_name,
                           ConstantFun alpha_fun,
                           const bool assemble_transpose = false,
                           const bool only_transpose = false)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL),
        alphaConstant(alpha_fun) {
    this->assembleTranspose = assemble_transpose;
    this->onlyTranspose = only_transpose;
  }
 
protected:
  FTensor::Index<'i', SPACE_DIM> i; ///< summit Index
  ConstantFun alphaConstant;
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
template <int SPACE_DIM, IntegrationType I, typename OpBase>
struct OpMixTensorTimesGradImpl {};
 
template <int SPACE_DIM, typename OpBase>
struct OpMixTensorTimesGradImpl<SPACE_DIM, GAUSS, OpBase> : public OpBase {
 
  OpMixTensorTimesGradImpl(const std::string row_field_name,
                           const std::string col_field_name,
                           ConstantFun alpha_fun, const bool assemble_transpose,
                           const bool only_transpose = false)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL),
        alphaConstant(alpha_fun) {
    this->assembleTranspose = assemble_transpose;
    this->onlyTranspose = only_transpose;
  }
 
  OpMixTensorTimesGradImpl(const std::string row_field_name,
                           const std::string col_field_name,
                           ConstantFun alpha_fun, ScalarFun beta_coeff,
                           const bool assemble_transpose,
                           const bool only_transpose = false)
      : OpBase(row_field_name, col_field_name, OpBase::OPROWCOL),
        alphaConstant(alpha_fun), betaCoeff(beta_coeff) {
    this->assembleTranspose = assemble_transpose;
    this->onlyTranspose = only_transpose;
  }
 
protected:
  FTensor::Index<'i', SPACE_DIM> i; ///< summit Index
  FTensor::Index<'j', SPACE_DIM> j; ///< summit Index
  ConstantFun alphaConstant = []() constexpr { return 1; };
  ScalarFun betaCoeff = [](double, double, double) constexpr { return 1; };
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
};
 
/**
 * @brief Bilinear integrator form
 * @ingroup mofem_forms
 *
 * @tparam EleOp
 * @tparam A
 * @tparam I
 */
template <typename EleOp>
template <AssemblyType A>
template <IntegrationType I>
struct FormsIntegrators<EleOp>::Assembly<A>::BiLinearForm {
 
  /**
   * @brief Integrate \f$(v_{,i},\beta(\mathbf{x}) u_{,j}))_\Omega\f$
   * @ingroup mofem_forms
   *
   * @tparam SPACE_DIM
   */
  template <int BASE_DIM, int FIELD_DIM, int SPACE_DIM>
  using OpGradGrad = OpGradGradImpl<BASE_DIM, FIELD_DIM, SPACE_DIM, I, OpBase>;
 
  /**
   * @brief Integrate \f$(v_i,\beta(\mathbf{x}) u_j)_\Omega\f$
   * @ingroup mofem_forms
   *
   * @note That FIELD_DIM = 4 or 9 is assumed that OpMass is for tensorial field
   * 2x2 or 3x3
   *
   * @todo It should be considered another template parameter RANK which will
   * allow to distinguish between scalar, vectorial and tensorial fields
   *
   * @tparam BASE_DIM dimension of base
   * @tparam FIELD_DIM dimension of field
   */
  template <int BASE_DIM, int FIELD_DIM>
  using OpMass = OpMassImpl<BASE_DIM, FIELD_DIM, I, OpBase>;
 
  /**
   * @brief Integrate \f$(v_k,D_{ijkl} u_{,l})_\Omega\f$
   *
   * \note \f$D_{ijkl}\f$ is * tensor with minor & major symmetry
   *
   * @ingroup mofem_forms
   *
   * @tparam SPACE_DIM
   * @tparam S
   */
  template <int BASE_DIM, int FIELD_DIM, int SPACE_DIM, int S = 0>
  using OpGradSymTensorGrad =
      OpGradSymTensorGradImpl<BASE_DIM, FIELD_DIM, SPACE_DIM, S, I, OpBase>;
 
  /**
   * @brief Integrate \f$(v_{,ij},D_{ijkl} u_{,kl})_\Omega\f$
   *
   * \note \f$D_{ijkl}\f$ is * tensor with no symmetries
   *
   * @ingroup mofem_forms
   *
   * @tparam SPACE_DIM
   * @tparam S
   */
  template <int BASE_DIM, int FIELD_DIM, int SPACE_DIM, int S = 0>
  using OpGradGradSymTensorGradGrad =
      OpGradGradSymTensorGradGradImpl<BASE_DIM, FIELD_DIM, SPACE_DIM, S, I,
                                      OpBase>;
 
  /**
   * @brief Integrate \f$(v_{,j},D_{ijkl} u_{,l})_\Omega\f$
   *
   * \note \f$D_{ijkl}\f$ is * tensor with no symmetries
   *
   * @ingroup mofem_forms
   *
   * @tparam SPACE_DIM
   * @tparam S
   */
  template <int BASE_DIM, int FIELD_DIM, int SPACE_DIM, int S = 0>
  using OpGradTensorGrad =
      OpGradTensorGradImpl<BASE_DIM, FIELD_DIM, SPACE_DIM, S, I, OpBase>;
 
  /**
   * @brief Integrate \f$(\lambda_{i,i},u)_\Omega\f$
   *
   * @tparam SPACE_DIM
   */
  template <int SPACE_DIM>
  using OpMixDivTimesScalar = OpMixDivTimesScalarImpl<SPACE_DIM, I, OpBase>;
 
  /**
   * @brief Integrate \f$(\lambda_{ij,j},u_{i})_\Omega\f$
   *
   * @tparam SPACE_DIM
   */
  template <int SPACE_DIM, CoordinateTypes CoordSys = CARTESIAN>
  using OpMixDivTimesVec = OpMixDivTimesVecImpl<SPACE_DIM, I, OpBase, CoordSys>;
 
  /**
   * @brief Integrate \f$(\lambda,u_{i,i})_\Omega\f$
   *
   * @tparam SPACE_DIM
   */
  template <int SPACE_DIM, CoordinateTypes COORDINATE_SYSTEM = CARTESIAN>
  using OpMixScalarTimesDiv =
      OpMixScalarTimesDivImpl<SPACE_DIM, I, OpBase, COORDINATE_SYSTEM>;
 
  /**
   * @brief Integrate \f$(\lambda_{i},u_{,j})_\Omega\f$
   *
   * @tparam SPACE_DIM
   */
  template <int BASE_DIM, int FIELD_DIM, int SPACE_DIM>
  using OpMixVectorTimesGrad =
      OpMixVectorTimesGradImpl<BASE_DIM, FIELD_DIM, SPACE_DIM, I, OpBase>;
 
  /**
   * @brief Integrate \f$(\lambda_{ij},u_{i,j})_\Omega\f$
   *
   * @tparam SPACE_DIM
   */
  template <int SPACE_DIM>
  using OpMixTensorTimesGrad = OpMixTensorTimesGradImpl<SPACE_DIM, I, OpBase>;
};
 
template <int SPACE_DIM, typename OpBase>
MoFEMErrorCode OpGradGradImpl<1, 1, SPACE_DIM, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  // get element volume
  const double vol = OpBase::getMeasure();
  // get integration weights
  auto t_w = OpBase::getFTensor0IntegrationWeight();
  // get base function gradient on rows
  auto t_row_grad = row_data.getFTensor1DiffN<SPACE_DIM>();
  // get coordinate at integration points
  auto t_coords = OpBase::getFTensor1CoordsAtGaussPts();
 
  // loop over integration points
  for (int gg = 0; gg != OpBase::nbIntegrationPts; gg++) {
    const double beta = vol * betaCoeff(t_coords(0), t_coords(1), t_coords(2));
    // take into account Jacobian
    const double alpha = t_w * beta;
    // loop over ros base functions
    int rr = 0;
    for (; rr != OpBase::nbRows; rr++) {
      // get column base functions gradient at gauss point gg
      auto t_col_grad = col_data.getFTensor1DiffN<SPACE_DIM>(gg, 0);
      // loop over columns
      for (int cc = 0; cc != OpBase::nbCols; cc++) {
        // calculate element of local matrix
        OpBase::locMat(rr, cc) += alpha * (t_row_grad(i) * t_col_grad(i));
        ++t_col_grad; // move to another gradient of base function
                      // on column
      }
      ++t_row_grad; // move to another element of gradient of base
                    // function on row
    }
    for (; rr < OpBase::nbRowBaseFunctions; ++rr)
      ++t_row_grad;
 
    ++t_coords;
    ++t_w; // move to another integration weight
  }
  MoFEMFunctionReturn(0);
}
 
template <int FIELD_DIM, int SPACE_DIM, typename OpBase>
MoFEMErrorCode
OpGradGradImpl<1, FIELD_DIM, SPACE_DIM, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  // get element volume
  const double vol = OpBase::getMeasure();
  // get integration weights
  auto t_w = OpBase::getFTensor0IntegrationWeight();
  // get base function gradient on rows
  auto t_row_grad = row_data.getFTensor1DiffN<SPACE_DIM>();
  // get coordinate at integration points
  auto t_coords = OpBase::getFTensor1CoordsAtGaussPts();
 
  FTensor::Index<'i', SPACE_DIM> i;
  FTensor::Index<'j', FIELD_DIM> j;
 
  auto get_t_vec = [&](const int rr) {
    std::array<double *, FIELD_DIM> ptrs;
    for (auto i = 0; i != FIELD_DIM; ++i)
      ptrs[i] = &OpBase::locMat(rr + i, i);
    return FTensor::Tensor1<FTensor::PackPtr<double *, FIELD_DIM>, FIELD_DIM>(
        ptrs);
  };
 
  // loop over integration points
  for (int gg = 0; gg != OpBase::nbIntegrationPts; gg++) {
    const double beta = vol * betaCoeff(t_coords(0), t_coords(1), t_coords(2));
    // take into account Jacobian
    const double alpha = t_w * beta;
    // loop over ros base functions
    int rr = 0;
    for (; rr != OpBase::nbRows / FIELD_DIM; rr++) {
      // get diag vec
      auto t_vec = get_t_vec(rr * FIELD_DIM);
      // get column base functions gradient at gauss point gg
      auto t_col_grad = col_data.getFTensor1DiffN<SPACE_DIM>(gg, 0);
      // loop over columns
      for (int cc = 0; cc != OpBase::nbCols / FIELD_DIM; cc++) {
        // calculate element of local matrix
        t_vec(j) += alpha * (t_row_grad(i) * t_col_grad(i));
        ++t_col_grad; // move to another gradient of base function
                      // on column
        ++t_vec;
      }
      ++t_row_grad; // move to another element of gradient of base
                    // function on row
    }
    for (; rr < OpBase::nbRowBaseFunctions; ++rr)
      ++t_row_grad;
 
    ++t_coords;
    ++t_w; // move to another integration weight
  }
  MoFEMFunctionReturn(0);
}
 
template <typename OpBase>
MoFEMErrorCode OpMassImpl<1, 1, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
#ifndef NDEBUG
  auto log_error = [&]() {
    MOFEM_LOG("SELF", Sev::error) << "Row side " << OpBase::rowSide << " "
                                  << CN::EntityTypeName(OpBase::rowType);
    MOFEM_LOG("SELF", Sev::error) << "Col side " << OpBase::colSide << " "
                                  << CN::EntityTypeName(OpBase::colType);
  };
 
  if (row_data.getN().size2() < OpBase::nbRows) {
    log_error();
    SETERRQ2(PETSC_COMM_SELF, MOFEM_DATA_INCONSISTENCY,
             "Wrong number of base functions on rows %d < %d",
             row_data.getN().size2(), OpBase::nbRows);
  }
  if (col_data.getN().size2() < OpBase::nbCols) {
    log_error();
    SETERRQ2(PETSC_COMM_SELF, MOFEM_DATA_INCONSISTENCY,
             "Wrong number of base functions on cols %d < %d",
             col_data.getN().size2(), OpBase::nbCols);
  }
  if (row_data.getN().size1() != OpBase::nbIntegrationPts) {
    log_error();
    SETERRQ2(PETSC_COMM_SELF, MOFEM_DATA_INCONSISTENCY,
             "Wrong number of integration points on rows %d != %d",
             row_data.getN().size1(), OpBase::nbIntegrationPts);
  }
  if (col_data.getN().size1() != OpBase::nbIntegrationPts) {
    log_error();
    SETERRQ2(PETSC_COMM_SELF, MOFEM_DATA_INCONSISTENCY,
             "Wrong number of integration points on cols %d != %d",
             col_data.getN().size1(), OpBase::nbIntegrationPts);
  }
#endif
 
  // get element volume
  const double vol = OpBase::getMeasure();
  // get integration weights
  auto t_w = OpBase::getFTensor0IntegrationWeight();
  // get base function gradient on rows
  auto t_row_base = row_data.getFTensor0N();
  // get coordinate at integration points
  auto t_coords = OpBase::getFTensor1CoordsAtGaussPts();
  // loop over integration points
  for (int gg = 0; gg != OpBase::nbIntegrationPts; gg++) {
    const double beta = vol * betaCoeff(t_coords(0), t_coords(1), t_coords(2));
    // take into account Jacobian
    const double alpha = t_w * beta;
    // loop over rows base functions
    auto a_mat_ptr = &*OpBase::locMat.data().begin();
    int rr = 0;
    for (; rr != OpBase::nbRows; rr++) {
      // get column base functions gradient at gauss point gg
      auto t_col_base = col_data.getFTensor0N(gg, 0);
      // loop over columns
      for (int cc = 0; cc != OpBase::nbCols; cc++) {
        // calculate element of local matrix
        *a_mat_ptr += alpha * (t_row_base * t_col_base);
        ++t_col_base;
        ++a_mat_ptr;
      }
      ++t_row_base;
    }
    for (; rr < OpBase::nbRowBaseFunctions; ++rr)
      ++t_row_base;
    ++t_coords;
    ++t_w; // move to another integration weight
  }
  MoFEMFunctionReturn(0);
};
 
template <int FIELD_DIM, typename OpBase>
MoFEMErrorCode OpMassImpl<1, FIELD_DIM, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
  // get element volume
  const double vol = OpBase::getMeasure();
  // get integration weights
  auto t_w = OpBase::getFTensor0IntegrationWeight();
  // get base function gradient on rows
  auto t_row_base = row_data.getFTensor0N();
  // get coordinate at integration points
  auto t_coords = OpBase::getFTensor1CoordsAtGaussPts();
 
  FTensor::Index<'i', FIELD_DIM> i;
  auto get_t_vec = [&](const int rr) {
    std::array<double *, FIELD_DIM> ptrs;
    for (auto i = 0; i != FIELD_DIM; ++i)
      ptrs[i] = &OpBase::locMat(rr + i, i);
    return FTensor::Tensor1<FTensor::PackPtr<double *, FIELD_DIM>, FIELD_DIM>(
        ptrs);
  };
 
  // loop over integration points
  for (int gg = 0; gg != OpBase::nbIntegrationPts; gg++) {
    const double beta = vol * betaCoeff(t_coords(0), t_coords(1), t_coords(2));
    // take into account Jacobian
    const double alpha = t_w * beta;
    // loop over rows base functions
    int rr = 0;
    for (; rr != OpBase::nbRows / FIELD_DIM; rr++) {
      // get column base functions gradient at gauss point gg
      auto t_col_base = col_data.getFTensor0N(gg, 0);
      // get mat vec
      auto t_vec = get_t_vec(FIELD_DIM * rr);
      // loop over columns
      for (int cc = 0; cc != OpBase::nbCols / FIELD_DIM; cc++) {
        // calculate element of local matrix
        t_vec(i) += alpha * (t_row_base * t_col_base);
        ++t_col_base;
        ++t_vec;
      }
      ++t_row_base;
    }
    for (; rr < OpBase::nbRowBaseFunctions; ++rr)
      ++t_row_base;
    ++t_coords;
    ++t_w; // move to another integration weight
  }
  MoFEMFunctionReturn(0);
};
 
template <int FIELD_DIM, typename OpBase>
MoFEMErrorCode OpMassImpl<3, FIELD_DIM, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  FTensor::Index<'i', FIELD_DIM> i;
  MoFEMFunctionBegin;
  size_t nb_base_functions = row_data.getN().size2() / 3;
  // // get element volume
  const double vol = OpBase::getMeasure();
  // get integration weights
  auto t_w = OpBase::getFTensor0IntegrationWeight();
  // get base function gradient on rows
  auto t_row_base = row_data.getFTensor1N<3>();
  // get coordinate at integration points
  auto t_coords = OpBase::getFTensor1CoordsAtGaussPts();
  // loop over integration points
  for (int gg = 0; gg != OpBase::nbIntegrationPts; gg++) {
    const double beta = vol * betaCoeff(t_coords(0), t_coords(1), t_coords(2));
    // take into account Jacobian
    const double alpha = t_w * beta;
    // loop over rows base functions
    auto a_mat_ptr = &*OpBase::locMat.data().begin();
    int rr = 0;
    for (; rr != OpBase::nbRows; rr++) {
      // get column base functions gradient at gauss point gg
      auto t_col_base = col_data.getFTensor1N<3>(gg, 0);
      // loop over columns
      for (int cc = 0; cc != OpBase::nbCols; cc++) {
        // calculate element of local matrix
        (*a_mat_ptr) += alpha * (t_row_base(i) * t_col_base(i));
        ++t_col_base;
        ++a_mat_ptr;
      }
      ++t_row_base;
    }
    for (; rr < nb_base_functions; ++rr)
      ++t_row_base;
    ++t_coords;
    ++t_w; // move to another integration weight
  }
  MoFEMFunctionReturn(0);
};
 
template <typename OpBase>
MoFEMErrorCode OpMassImpl<3, 4, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
  FTensor::Index<'i', 2> I;
  FTensor::Index<'k', 3> k;
  auto get_t_vec = [&](const int rr) {
    return FTensor::Tensor1<FTensor::PackPtr<double *, 2>, 2>{
        &OpBase::locMat(rr + 0, 0), &OpBase::locMat(rr + 1, 1)};
  };
  size_t nb_base_functions = row_data.getN().size2() / 3;
  // // get element volume
  const double vol = OpBase::getMeasure();
  // get integration weights
  auto t_w = OpBase::getFTensor0IntegrationWeight();
  // get base function gradient on rows
  auto t_row_base = row_data.getFTensor1N<3>();
  // get coordinate at integration points
  auto t_coords = OpBase::getFTensor1CoordsAtGaussPts();
  // loop over integration points
  for (int gg = 0; gg != OpBase::nbIntegrationPts; gg++) {
    const double beta = vol * betaCoeff(t_coords(0), t_coords(1), t_coords(2));
    // take into account Jacobian
    const double alpha = t_w * beta;
    // loop over rows base functions
    int rr = 0;
    for (; rr != OpBase::nbRows / 2; rr++) {
      // get column base functions gradient at gauss point gg
      auto t_col_base = col_data.getFTensor1N<3>(gg, 0);
      auto t_vec = get_t_vec(2 * rr);
      // loop over columns
      for (int cc = 0; cc != OpBase::nbCols / 2; cc++) {
        // calculate element of local matrix
        t_vec(I) += alpha * (t_row_base(k) * t_col_base(k));
        ++t_col_base;
        ++t_vec;
      }
      ++t_row_base;
    }
    for (; rr < nb_base_functions; ++rr)
      ++t_row_base;
    ++t_coords;
    ++t_w; // move to another integration weight
  }
  MoFEMFunctionReturn(0);
}
 
template <typename OpBase>
MoFEMErrorCode OpMassImpl<3, 9, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
  FTensor::Index<'i', 3> i;
  FTensor::Index<'k', 3> k;
  auto get_t_vec = [&](const int rr) {
    return FTensor::Tensor1<FTensor::PackPtr<double *, 3>, 3>{
        &OpBase::locMat(rr + 0, 0), &OpBase::locMat(rr + 1, 1),
        &OpBase::locMat(rr + 2, 2)};
  };
  size_t nb_base_functions = row_data.getN().size2() / 3;
  // // get element volume
  const double vol = OpBase::getMeasure();
  // get integration weights
  auto t_w = OpBase::getFTensor0IntegrationWeight();
  // get base function gradient on rows
  auto t_row_base = row_data.getFTensor1N<3>();
  // get coordinate at integration points
  auto t_coords = OpBase::getFTensor1CoordsAtGaussPts();
  // loop over integration points
  for (int gg = 0; gg != OpBase::nbIntegrationPts; gg++) {
    const double beta = vol * betaCoeff(t_coords(0), t_coords(1), t_coords(2));
    // take into account Jacobian
    const double alpha = t_w * beta;
    // loop over rows base functions
    int rr = 0;
    for (; rr != OpBase::nbRows / 3; rr++) {
      // get column base functions gradient at gauss point gg
      auto t_col_base = col_data.getFTensor1N<3>(gg, 0);
      auto t_vec = get_t_vec(3 * rr);
      // loop over columns
      for (int cc = 0; cc != OpBase::nbCols / 3; cc++) {
        // calculate element of local matrix
        t_vec(i) += alpha * (t_row_base(k) * t_col_base(k));
        ++t_col_base;
        ++t_vec;
      }
      ++t_row_base;
    }
    for (; rr < nb_base_functions; ++rr)
      ++t_row_base;
    ++t_coords;
    ++t_w; // move to another integration weight
  }
  MoFEMFunctionReturn(0);
};
 
template <int SPACE_DIM, int S, typename OpBase>
MoFEMErrorCode
OpGradSymTensorGradImpl<1, SPACE_DIM, SPACE_DIM, S, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  const size_t nb_row_dofs = row_data.getIndices().size();
  const size_t nb_col_dofs = col_data.getIndices().size();
 
  if (nb_row_dofs && nb_col_dofs) {
 
    const bool diag = (row_data.getFieldEntities()[0]->getLocalUniqueId() ==
                       col_data.getFieldEntities()[0]->getLocalUniqueId());
 
    FTensor::Index<'i', SPACE_DIM> i;
    FTensor::Index<'j', SPACE_DIM> j;
    FTensor::Index<'k', SPACE_DIM> k;
    FTensor::Index<'l', SPACE_DIM> l;
 
    // get element volume
    double vol = OpBase::getMeasure();
 
    // get intergrayion weights
    auto t_w = OpBase::getFTensor0IntegrationWeight();
 
    // get derivatives of base functions on rows
    auto t_row_diff_base = row_data.getFTensor1DiffN<SPACE_DIM>();
 
    // Elastic stiffness tensor (4th rank tensor with minor and major
    // symmetry)
    auto t_D = getFTensor4DdgFromMat<SPACE_DIM, SPACE_DIM, S>(*matD);
 
    // get coordinate at integration points
    auto t_coords = OpBase::getFTensor1CoordsAtGaussPts();
 
    // iterate over integration points
    for (int gg = 0; gg != OpBase::nbIntegrationPts; ++gg) {
 
      // calculate scalar weight times element volume
      double a = t_w * vol * betaCoeff(t_coords(0), t_coords(1), t_coords(2));
 
      // iterate over row base functions
      int rr = 0;
      for (; rr != OpBase::nbRows / SPACE_DIM; ++rr) {
 
        // get sub matrix for the row
        auto t_m = OpBase::template getLocMat<SPACE_DIM>(SPACE_DIM * rr);
 
        FTensor::Christof<double, SPACE_DIM, SPACE_DIM> t_rowD;
        // I mix up the indices here so that it behaves like a
        // Dg.  That way I don't have to have a separate wrapper
        // class Christof_Expr, which simplifies things.
        t_rowD(l, j, k) = t_D(i, j, k, l) * (a * t_row_diff_base(i));
 
        // get derivatives of base functions for columns
        auto t_col_diff_base = col_data.getFTensor1DiffN<SPACE_DIM>(gg, 0);
 
        // iterate column base functions
        const auto nb_cols = (diag) ? rr : OpBase::nbCols / SPACE_DIM - 1;
        for (int cc = 0; cc <= nb_cols; ++cc) {
 
          // integrate block local stiffens matrix
          t_m(i, j) += t_rowD(i, j, k) * t_col_diff_base(k);
 
          // move to next column base function
          ++t_col_diff_base;
 
          // move to next block of local stiffens matrix
          ++t_m;
        }
 
        // move to next row base function
        ++t_row_diff_base;
      }
 
      for (; rr < OpBase::nbRowBaseFunctions; ++rr)
        ++t_row_diff_base;
 
      // move to next integration weight
      ++t_w;
      ++t_D;
      ++t_coords;
    }
 
    // Copy symmetry
    if (diag) {
      for (int rr = 0; rr != OpBase::nbRows / SPACE_DIM - 1; ++rr) {
        auto t_m_rr = getFTensor2FromArray<SPACE_DIM, SPACE_DIM, SPACE_DIM>(
            this->locMat, SPACE_DIM * rr, SPACE_DIM * (rr + 1));
        auto t_m_cc = getFTensor2FromArray<SPACE_DIM, SPACE_DIM>(
            this->locMat, SPACE_DIM * (rr + 1), SPACE_DIM * rr,
            SPACE_DIM * OpBase::nbCols);
        for (int cc = rr + 1; cc < OpBase::nbCols / SPACE_DIM; ++cc) {
          t_m_rr(i, j) = t_m_cc(j, i);
          ++t_m_rr;
          ++t_m_cc;
        }
      }
    }
  }
 
  MoFEMFunctionReturn(0);
}
 
template <int SPACE_DIM, int S, typename OpBase>
MoFEMErrorCode
OpGradGradSymTensorGradGradImpl<1, 1, SPACE_DIM, S, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  if (OpBase::nbRows && OpBase::nbCols) {
 
    FTensor::Index<'i', SPACE_DIM> i;
    FTensor::Index<'j', SPACE_DIM> j;
    FTensor::Index<'k', SPACE_DIM> k;
    FTensor::Index<'l', SPACE_DIM> l;
 
    auto &row_hessian = row_data.getN(BaseDerivatives::SecondDerivative);
    auto &col_hessian = col_data.getN(BaseDerivatives::SecondDerivative);
 
#ifndef NDEBUG
    if (row_hessian.size1() != OpBase::nbIntegrationPts) {
      SETERRQ2(PETSC_COMM_SELF, MOFEM_DATA_INCONSISTENCY,
               "Wrong number of integration pts (%d != %d)",
               row_hessian.size1(), OpBase::nbIntegrationPts);
    }
    if (row_hessian.size2() !=
        OpBase::nbRowBaseFunctions * SPACE_DIM * SPACE_DIM) {
      SETERRQ2(PETSC_COMM_SELF, MOFEM_DATA_INCONSISTENCY,
               "Wrong number of base functions (%d != %d)",
               row_hessian.size2() / (SPACE_DIM * SPACE_DIM),
               OpBase::nbRowBaseFunctions);
    }
    if (row_hessian.size2() < OpBase::nbRows * SPACE_DIM * SPACE_DIM) {
      SETERRQ2(PETSC_COMM_SELF, MOFEM_DATA_INCONSISTENCY,
               "Wrong number of base functions (%d < %d)", row_hessian.size2(),
               OpBase::nbRows * SPACE_DIM * SPACE_DIM);
    }
    if (col_hessian.size1() != OpBase::nbIntegrationPts) {
      SETERRQ2(PETSC_COMM_SELF, MOFEM_DATA_INCONSISTENCY,
               "Wrong number of integration pts (%d != %d)",
               col_hessian.size1(), OpBase::nbIntegrationPts);
    }
    if (col_hessian.size2() < OpBase::nbCols * SPACE_DIM * SPACE_DIM) {
      SETERRQ2(PETSC_COMM_SELF, MOFEM_DATA_INCONSISTENCY,
               "Wrong number of base functions (%d < %d)", col_hessian.size2(),
               OpBase::nbRows * SPACE_DIM * SPACE_DIM);
    }
#endif
 
    // get element volume
    double vol = OpBase::getMeasure();
 
    // get intergrayion weights
    auto t_w = OpBase::getFTensor0IntegrationWeight();
 
    auto t_row_diff2 = getFTensor2SymmetricLowerFromPtr<SPACE_DIM>(
        &*row_hessian.data().begin());
 
    // Elastic stiffness tensor (4th rank tensor with minor and major
    // symmetry)
    auto t_D = getFTensor4DdgFromMat<SPACE_DIM, SPACE_DIM, S>(*matD);
 
    // iterate over integration points
    for (int gg = 0; gg != OpBase::nbIntegrationPts; ++gg) {
 
      // calculate scalar weight times element volume
      double a = t_w * vol;
 
      // get sub matrix for the row
      auto m_ptr = &*OpBase::locMat.data().begin();
 
      // iterate over row base functions
      int rr = 0;
      for (; rr != OpBase::nbRows; ++rr) {
 
        FTensor::Tensor2_symmetric<double, SPACE_DIM> t_rowD;
        t_rowD(k, l) = t_D(i, j, k, l) * (a * t_row_diff2(i, j));
 
        // get derivatives of base functions for columns
        auto t_col_diff2 =
            getFTensor2SymmetricLowerFromPtr<SPACE_DIM>(&col_hessian(gg, 0));
 
        // iterate column base functions
        for (int cc = 0; cc != OpBase::nbCols; ++cc) {
 
          // integrate block local stiffens matrix
          *m_ptr += t_rowD(i, j) * t_col_diff2(i, j);
 
          // move to next column base function
          ++t_col_diff2;
 
          // move to next block of local stiffens matrix
          ++m_ptr;
        }
 
        // move to next row base function
        ++t_row_diff2;
      }
 
      for (; rr < OpBase::nbRowBaseFunctions; ++rr)
        ++t_row_diff2;
 
      // move to next integration weight
      ++t_w;
      ++t_D;
    }
  }
 
  MoFEMFunctionReturn(0);
}
 
template <int SPACE_DIM, int S, typename OpBase>
MoFEMErrorCode
OpGradTensorGradImpl<1, SPACE_DIM, SPACE_DIM, S, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  const size_t nb_row_dofs = row_data.getIndices().size();
  const size_t nb_col_dofs = col_data.getIndices().size();
 
  if (nb_row_dofs && nb_col_dofs) {
 
    FTensor::Index<'i', SPACE_DIM> i;
    FTensor::Index<'j', SPACE_DIM> j;
    FTensor::Index<'k', SPACE_DIM> k;
    FTensor::Index<'l', SPACE_DIM> l;
 
    // get element volume
    double vol = OpBase::getMeasure();
 
    // get intergrayion weights
    auto t_w = OpBase::getFTensor0IntegrationWeight();
 
    // get derivatives of base functions on rows
    auto t_row_diff_base = row_data.getFTensor1DiffN<SPACE_DIM>();
 
    // stiffness tensor (4th rank tensor)
    auto t_D =
        getFTensor4FromMat<SPACE_DIM, SPACE_DIM, SPACE_DIM, SPACE_DIM, S>(
            *matD);
 
    // get coordinate at integration points
    auto t_coords = OpBase::getFTensor1CoordsAtGaussPts();
 
    // iterate over integration points
    for (int gg = 0; gg != OpBase::nbIntegrationPts; ++gg) {
 
      // calculate scalar weight times element volume
      double a = t_w * vol * betaCoeff(t_coords(0), t_coords(1), t_coords(2));
 
      // iterate over row base functions
      int rr = 0;
      for (; rr != OpBase::nbRows / SPACE_DIM; ++rr) {
 
        // get sub matrix for the row
        auto t_m = OpBase::template getLocMat<SPACE_DIM>(SPACE_DIM * rr);
 
        // calculate row
        FTensor::Tensor3<double, 3, 3, 3> t_row;
        t_row(i, k, l) = t_D(i, j, k, l) * (a * t_row_diff_base(j));
 
        // get derivatives of base functions for columns
        auto t_col_diff_base = col_data.getFTensor1DiffN<SPACE_DIM>(gg, 0);
 
        // iterate column base functions
        for (int cc = 0; cc != OpBase::nbCols / SPACE_DIM; ++cc) {
 
          // integrate block local stiffens matrix
          t_m(i, k) += t_row(i, k, l) * t_col_diff_base(l);
 
          // move to next column base function
          ++t_col_diff_base;
 
          // move to next block of local stiffens matrix
          ++t_m;
        }
 
        // move to next row base function
        ++t_row_diff_base;
      }
 
      for (; rr < OpBase::nbRowBaseFunctions; ++rr)
        ++t_row_diff_base;
 
      // move to next integration weight
      ++t_w;
      ++t_D;
      ++t_coords;
    }
  }
 
  MoFEMFunctionReturn(0);
}
 
template <int SPACE_DIM, typename OpBase>
MoFEMErrorCode OpMixDivTimesScalarImpl<SPACE_DIM, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  auto t_w = this->getFTensor0IntegrationWeight();
 
  size_t nb_base_functions = row_data.getN().size2() / 3;
  auto t_row_diff_base = row_data.getFTensor2DiffN<3, SPACE_DIM>();
 
  const double alpha_constant = alphaConstant();
 
  for (size_t gg = 0; gg != OpBase::nbIntegrationPts; ++gg) {
    const double alpha = alpha_constant * this->getMeasure() * t_w;
 
    size_t rr = 0;
    for (; rr != OpBase::nbRows; ++rr) {
      const double t_row_div_base = t_row_diff_base(i, i);
      auto t_col_base = col_data.getFTensor0N(gg, 0);
      for (size_t cc = 0; cc != OpBase::nbCols; ++cc) {
        this->locMat(rr, cc) += alpha * t_row_div_base * t_col_base;
        ++t_col_base;
      }
      ++t_row_diff_base;
    }
    for (; rr < nb_base_functions; ++rr)
      ++t_row_diff_base;
 
    ++t_w;
  }
 
  MoFEMFunctionReturn(0);
}
 
template <int SPACE_DIM, typename OpBase, CoordinateTypes CoordSys>
MoFEMErrorCode
OpMixDivTimesVecImpl<SPACE_DIM, GAUSS, OpBase, CoordSys>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  auto t_w = this->getFTensor0IntegrationWeight();
  auto t_coords = this->getFTensor1CoordsAtGaussPts();
 
  size_t nb_base_functions = row_data.getN().size2() / 3;
  auto t_row_diff_base = row_data.getFTensor2DiffN<3, SPACE_DIM>();
  auto t_row_base = row_data.getFTensor1N<3>();
  const double alpha_constant = alphaConstant() * this->getMeasure();
  for (size_t gg = 0; gg != OpBase::nbIntegrationPts; ++gg) {
 
    const double alpha =
        alpha_constant * t_w * betaCoeff(t_coords(0), t_coords(1), t_coords(2));
 
    size_t rr = 0;
    for (; rr != OpBase::nbRows / SPACE_DIM; ++rr) {
      auto t_mat_diag = getFTensor1FromArrayDiag<SPACE_DIM, SPACE_DIM>(
          this->locMat, SPACE_DIM * rr);
      const double t_row_div_base = t_row_diff_base(i, i);
      auto t_col_base = col_data.getFTensor0N(gg, 0);
 
      for (size_t cc = 0; cc != OpBase::nbCols / SPACE_DIM; ++cc) {
        t_mat_diag(i) += alpha * t_row_div_base * t_col_base;
        if constexpr (CoordSys == CYLINDRICAL) {
          t_mat_diag(i) += t_row_base(0) * (alpha / t_coords(0)) * t_col_base;
        }
        ++t_col_base;
        ++t_mat_diag;
      }
      ++t_row_base;
      ++t_row_diff_base;
    }
    for (; rr < nb_base_functions; ++rr) {
      ++t_row_diff_base;
      ++t_row_base;
    }
 
    ++t_w;
    ++t_coords;
  }
 
  MoFEMFunctionReturn(0);
}
 
template <int SPACE_DIM, typename OpBase, CoordinateTypes COORDINATE_SYSTEM>
MoFEMErrorCode
OpMixScalarTimesDivImpl<SPACE_DIM, GAUSS, OpBase, COORDINATE_SYSTEM>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
#ifndef NDEBUG
  if (OpBase::locMat.size2() % SPACE_DIM)
    SETERRQ(PETSC_COMM_SELF, MOFEM_DATA_INCONSISTENCY,
            "Number of rows in matrix should be multiple of space dimensions");
#endif
 
  // When we move to C++17 add if constexpr()
  if constexpr (COORDINATE_SYSTEM == POLAR || COORDINATE_SYSTEM == SPHERICAL)
    SETERRQ1(PETSC_COMM_SELF, MOFEM_NOT_IMPLEMENTED,
             "%s coordiante not implemented",
             CoordinateTypesNames[COORDINATE_SYSTEM]);
 
  auto t_w = this->getFTensor0IntegrationWeight();
  auto t_coords = this->getFTensor1CoordsAtGaussPts();
  size_t nb_base_functions_row = row_data.getN().size2();
  auto t_row_base = row_data.getFTensor0N();
  const double vol = this->getMeasure();
  for (size_t gg = 0; gg != OpBase::nbIntegrationPts; ++gg) {
 
    const double alpha =
        alphaConstant(t_coords(0), t_coords(1), t_coords(2)) * t_w * vol;
 
    size_t rr = 0;
    auto t_m = getFTensor1FromPtr<SPACE_DIM>(OpBase::locMat.data().data());
 
    // When we move to C++17 add if constexpr()
    if constexpr (COORDINATE_SYSTEM == CARTESIAN) {
      for (; rr != OpBase::nbRows; ++rr) {
        const double r_val = alpha * t_row_base;
        auto t_col_diff_base = col_data.getFTensor1DiffN<SPACE_DIM>(gg, 0);
        for (size_t cc = 0; cc != OpBase::nbCols / SPACE_DIM; ++cc) {
          t_m(i) += r_val * t_col_diff_base(i);
          ++t_col_diff_base;
          ++t_m;
        }
        ++t_row_base;
      }
    }
 
    // When we move to C++17 add if constexpr()
    if constexpr (COORDINATE_SYSTEM == CYLINDRICAL) {
      for (; rr != OpBase::nbRows; ++rr) {
        const double r_val = alpha * t_row_base;
        auto t_col_base = col_data.getFTensor0N(gg, 0);
        auto t_col_diff_base = col_data.getFTensor1DiffN<SPACE_DIM>(gg, 0);
        for (size_t cc = 0; cc != OpBase::nbCols / SPACE_DIM; ++cc) {
          t_m(i) += r_val * t_col_diff_base(i);
          t_m(0) += (r_val / t_coords(0)) * t_col_base;
          ++t_col_base;
          ++t_col_diff_base;
          ++t_m;
        }
        ++t_row_base;
      }
    }
 
    for (; rr < nb_base_functions_row; ++rr)
      ++t_row_base;
 
    ++t_w;
    ++t_coords;
  }
 
  MoFEMFunctionReturn(0);
}
 
template <int SPACE_DIM, typename OpBase>
MoFEMErrorCode
OpMixVectorTimesGradImpl<3, SPACE_DIM, SPACE_DIM, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  auto t_w = this->getFTensor0IntegrationWeight();
 
  size_t nb_base_functions = row_data.getN().size2() / 3;
  auto t_row_base = row_data.getFTensor1N<3>();
  auto &mat = this->locMat;
  const double alpha_constant = alphaConstant();
  for (size_t gg = 0; gg != OpBase::nbIntegrationPts; ++gg) {
 
    const double alpha = alpha_constant * this->getMeasure() * t_w;
 
    size_t rr = 0;
    for (; rr != OpBase::nbRows; ++rr) {
      auto t_col_diff_base = col_data.getFTensor1DiffN<SPACE_DIM>(gg, 0);
      for (size_t cc = 0; cc != OpBase::nbCols; ++cc) {
        mat(rr, cc) += alpha * t_row_base(i) * t_col_diff_base(i);
        ++t_col_diff_base;
      }
      ++t_row_base;
    }
    for (; rr < nb_base_functions; ++rr)
      ++t_row_base;
 
    ++t_w;
  }
 
  MoFEMFunctionReturn(0);
}
 
template <int SPACE_DIM, typename OpBase>
MoFEMErrorCode
OpMixVectorTimesGradImpl<1, SPACE_DIM, SPACE_DIM, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  auto t_w = this->getFTensor0IntegrationWeight();
 
  size_t nb_base_functions = row_data.getN().size2();
  auto t_row_base = row_data.getFTensor0N();
 
  auto get_t_vec = [&](const int rr) {
    std::array<double *, SPACE_DIM> ptrs;
    for (auto i = 0; i != SPACE_DIM; ++i)
      ptrs[i] = &OpBase::locMat(rr + i, 0);
    return FTensor::Tensor1<FTensor::PackPtr<double *, 1>, SPACE_DIM>(ptrs);
  };
 
  const double alpha_constant = alphaConstant();
  for (size_t gg = 0; gg != OpBase::nbIntegrationPts; ++gg) {
 
    const double alpha = alpha_constant * this->getMeasure() * t_w;
 
    size_t rr = 0;
    for (; rr != OpBase::nbRows / SPACE_DIM; ++rr) {
      auto t_vec = get_t_vec(SPACE_DIM * rr);
      auto t_col_diff_base = col_data.getFTensor1DiffN<SPACE_DIM>(gg, 0);
      for (size_t cc = 0; cc != OpBase::nbCols; ++cc) {
        t_vec(i) += alpha * t_row_base * t_col_diff_base(i);
        ++t_col_diff_base;
        ++t_vec;
      }
      ++t_row_base;
    }
    for (; rr < nb_base_functions; ++rr)
      ++t_row_base;
 
    ++t_w;
  }
 
  MoFEMFunctionReturn(0);
}
 
template <int SPACE_DIM, typename OpBase>
MoFEMErrorCode OpMixTensorTimesGradImpl<SPACE_DIM, GAUSS, OpBase>::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  auto t_w = this->getFTensor0IntegrationWeight();
  auto t_coords = this->getFTensor1CoordsAtGaussPts();
 
  size_t nb_base_functions = row_data.getN().size2() / 3;
  auto t_row_base = row_data.getFTensor1N<3>();
  const double alpha_constant = alphaConstant() * this->getMeasure();
  for (size_t gg = 0; gg != OpBase::nbIntegrationPts; ++gg) {
 
    const double alpha =
        alpha_constant * betaCoeff(t_coords(0), t_coords(1), t_coords(2)) * t_w;
 
    size_t rr = 0;
    for (; rr != OpBase::nbRows / SPACE_DIM; ++rr) {
      auto t_mat_diag = getFTensor1FromArrayDiag<SPACE_DIM, SPACE_DIM>(
          this->locMat, SPACE_DIM * rr);
      auto t_col_diff_base = col_data.getFTensor1DiffN<SPACE_DIM>(gg, 0);
 
      for (size_t cc = 0; cc != OpBase::nbCols / SPACE_DIM; ++cc) {
        t_mat_diag(i) += alpha * t_row_base(j) * t_col_diff_base(j);
        ++t_col_diff_base;
        ++t_mat_diag;
      }
 
      ++t_row_base;
    }
    for (; rr < nb_base_functions; ++rr)
      ++t_row_base;
 
    ++t_w;
    ++t_coords;
  }
 
  MoFEMFunctionReturn(0);
}
 
} // namespace MoFEM
 
#endif //__BILINEAR_FORMS_INTEGRATORS_HPP__